diff --git a/vendor/pouchdb-7.1.1.js b/vendor/pouchdb-7.1.1.js
new file mode 100644
index 0000000..c126978
--- /dev/null
+++ b/vendor/pouchdb-7.1.1.js
@@ -0,0 +1,12245 @@
+// PouchDB 7.1.1
+// 
+// (c) 2012-2019 Dale Harvey and the PouchDB team
+// PouchDB may be freely distributed under the Apache license, version 2.0.
+// For all details and documentation:
+// http://pouchdb.com
+(function(f){if(typeof exports==="object"&&typeof module!=="undefined"){module.exports=f()}else if(typeof define==="function"&&define.amd){define([],f)}else{var g;if(typeof window!=="undefined"){g=window}else if(typeof global!=="undefined"){g=global}else if(typeof self!=="undefined"){g=self}else{g=this}g.PouchDB = f()}})(function(){var define,module,exports;return (function(){function r(e,n,t){function o(i,f){if(!n[i]){if(!e[i]){var c="function"==typeof require&&require;if(!f&&c)return c(i,!0);if(u)return u(i,!0);var a=new Error("Cannot find module '"+i+"'");throw a.code="MODULE_NOT_FOUND",a}var p=n[i]={exports:{}};e[i][0].call(p.exports,function(r){var n=e[i][1][r];return o(n||r)},p,p.exports,r,e,n,t)}return n[i].exports}for(var u="function"==typeof require&&require,i=0;i<t.length;i++)o(t[i]);return o}return r})()({1:[function(_dereq_,module,exports){
+'use strict';
+
+module.exports = argsArray;
+
+function argsArray(fun) {
+  return function () {
+    var len = arguments.length;
+    if (len) {
+      var args = [];
+      var i = -1;
+      while (++i < len) {
+        args[i] = arguments[i];
+      }
+      return fun.call(this, args);
+    } else {
+      return fun.call(this, []);
+    }
+  };
+}
+},{}],2:[function(_dereq_,module,exports){
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var objectCreate = Object.create || objectCreatePolyfill
+var objectKeys = Object.keys || objectKeysPolyfill
+var bind = Function.prototype.bind || functionBindPolyfill
+
+function EventEmitter() {
+  if (!this._events || !Object.prototype.hasOwnProperty.call(this, '_events')) {
+    this._events = objectCreate(null);
+    this._eventsCount = 0;
+  }
+
+  this._maxListeners = this._maxListeners || undefined;
+}
+module.exports = EventEmitter;
+
+// Backwards-compat with node 0.10.x
+EventEmitter.EventEmitter = EventEmitter;
+
+EventEmitter.prototype._events = undefined;
+EventEmitter.prototype._maxListeners = undefined;
+
+// By default EventEmitters will print a warning if more than 10 listeners are
+// added to it. This is a useful default which helps finding memory leaks.
+var defaultMaxListeners = 10;
+
+var hasDefineProperty;
+try {
+  var o = {};
+  if (Object.defineProperty) Object.defineProperty(o, 'x', { value: 0 });
+  hasDefineProperty = o.x === 0;
+} catch (err) { hasDefineProperty = false }
+if (hasDefineProperty) {
+  Object.defineProperty(EventEmitter, 'defaultMaxListeners', {
+    enumerable: true,
+    get: function() {
+      return defaultMaxListeners;
+    },
+    set: function(arg) {
+      // check whether the input is a positive number (whose value is zero or
+      // greater and not a NaN).
+      if (typeof arg !== 'number' || arg < 0 || arg !== arg)
+        throw new TypeError('"defaultMaxListeners" must be a positive number');
+      defaultMaxListeners = arg;
+    }
+  });
+} else {
+  EventEmitter.defaultMaxListeners = defaultMaxListeners;
+}
+
+// Obviously not all Emitters should be limited to 10. This function allows
+// that to be increased. Set to zero for unlimited.
+EventEmitter.prototype.setMaxListeners = function setMaxListeners(n) {
+  if (typeof n !== 'number' || n < 0 || isNaN(n))
+    throw new TypeError('"n" argument must be a positive number');
+  this._maxListeners = n;
+  return this;
+};
+
+function $getMaxListeners(that) {
+  if (that._maxListeners === undefined)
+    return EventEmitter.defaultMaxListeners;
+  return that._maxListeners;
+}
+
+EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
+  return $getMaxListeners(this);
+};
+
+// These standalone emit* functions are used to optimize calling of event
+// handlers for fast cases because emit() itself often has a variable number of
+// arguments and can be deoptimized because of that. These functions always have
+// the same number of arguments and thus do not get deoptimized, so the code
+// inside them can execute faster.
+function emitNone(handler, isFn, self) {
+  if (isFn)
+    handler.call(self);
+  else {
+    var len = handler.length;
+    var listeners = arrayClone(handler, len);
+    for (var i = 0; i < len; ++i)
+      listeners[i].call(self);
+  }
+}
+function emitOne(handler, isFn, self, arg1) {
+  if (isFn)
+    handler.call(self, arg1);
+  else {
+    var len = handler.length;
+    var listeners = arrayClone(handler, len);
+    for (var i = 0; i < len; ++i)
+      listeners[i].call(self, arg1);
+  }
+}
+function emitTwo(handler, isFn, self, arg1, arg2) {
+  if (isFn)
+    handler.call(self, arg1, arg2);
+  else {
+    var len = handler.length;
+    var listeners = arrayClone(handler, len);
+    for (var i = 0; i < len; ++i)
+      listeners[i].call(self, arg1, arg2);
+  }
+}
+function emitThree(handler, isFn, self, arg1, arg2, arg3) {
+  if (isFn)
+    handler.call(self, arg1, arg2, arg3);
+  else {
+    var len = handler.length;
+    var listeners = arrayClone(handler, len);
+    for (var i = 0; i < len; ++i)
+      listeners[i].call(self, arg1, arg2, arg3);
+  }
+}
+
+function emitMany(handler, isFn, self, args) {
+  if (isFn)
+    handler.apply(self, args);
+  else {
+    var len = handler.length;
+    var listeners = arrayClone(handler, len);
+    for (var i = 0; i < len; ++i)
+      listeners[i].apply(self, args);
+  }
+}
+
+EventEmitter.prototype.emit = function emit(type) {
+  var er, handler, len, args, i, events;
+  var doError = (type === 'error');
+
+  events = this._events;
+  if (events)
+    doError = (doError && events.error == null);
+  else if (!doError)
+    return false;
+
+  // If there is no 'error' event listener then throw.
+  if (doError) {
+    if (arguments.length > 1)
+      er = arguments[1];
+    if (er instanceof Error) {
+      throw er; // Unhandled 'error' event
+    } else {
+      // At least give some kind of context to the user
+      var err = new Error('Unhandled "error" event. (' + er + ')');
+      err.context = er;
+      throw err;
+    }
+    return false;
+  }
+
+  handler = events[type];
+
+  if (!handler)
+    return false;
+
+  var isFn = typeof handler === 'function';
+  len = arguments.length;
+  switch (len) {
+      // fast cases
+    case 1:
+      emitNone(handler, isFn, this);
+      break;
+    case 2:
+      emitOne(handler, isFn, this, arguments[1]);
+      break;
+    case 3:
+      emitTwo(handler, isFn, this, arguments[1], arguments[2]);
+      break;
+    case 4:
+      emitThree(handler, isFn, this, arguments[1], arguments[2], arguments[3]);
+      break;
+      // slower
+    default:
+      args = new Array(len - 1);
+      for (i = 1; i < len; i++)
+        args[i - 1] = arguments[i];
+      emitMany(handler, isFn, this, args);
+  }
+
+  return true;
+};
+
+function _addListener(target, type, listener, prepend) {
+  var m;
+  var events;
+  var existing;
+
+  if (typeof listener !== 'function')
+    throw new TypeError('"listener" argument must be a function');
+
+  events = target._events;
+  if (!events) {
+    events = target._events = objectCreate(null);
+    target._eventsCount = 0;
+  } else {
+    // To avoid recursion in the case that type === "newListener"! Before
+    // adding it to the listeners, first emit "newListener".
+    if (events.newListener) {
+      target.emit('newListener', type,
+          listener.listener ? listener.listener : listener);
+
+      // Re-assign `events` because a newListener handler could have caused the
+      // this._events to be assigned to a new object
+      events = target._events;
+    }
+    existing = events[type];
+  }
+
+  if (!existing) {
+    // Optimize the case of one listener. Don't need the extra array object.
+    existing = events[type] = listener;
+    ++target._eventsCount;
+  } else {
+    if (typeof existing === 'function') {
+      // Adding the second element, need to change to array.
+      existing = events[type] =
+          prepend ? [listener, existing] : [existing, listener];
+    } else {
+      // If we've already got an array, just append.
+      if (prepend) {
+        existing.unshift(listener);
+      } else {
+        existing.push(listener);
+      }
+    }
+
+    // Check for listener leak
+    if (!existing.warned) {
+      m = $getMaxListeners(target);
+      if (m && m > 0 && existing.length > m) {
+        existing.warned = true;
+        var w = new Error('Possible EventEmitter memory leak detected. ' +
+            existing.length + ' "' + String(type) + '" listeners ' +
+            'added. Use emitter.setMaxListeners() to ' +
+            'increase limit.');
+        w.name = 'MaxListenersExceededWarning';
+        w.emitter = target;
+        w.type = type;
+        w.count = existing.length;
+        if (typeof console === 'object' && console.warn) {
+          console.warn('%s: %s', w.name, w.message);
+        }
+      }
+    }
+  }
+
+  return target;
+}
+
+EventEmitter.prototype.addListener = function addListener(type, listener) {
+  return _addListener(this, type, listener, false);
+};
+
+EventEmitter.prototype.on = EventEmitter.prototype.addListener;
+
+EventEmitter.prototype.prependListener =
+    function prependListener(type, listener) {
+      return _addListener(this, type, listener, true);
+    };
+
+function onceWrapper() {
+  if (!this.fired) {
+    this.target.removeListener(this.type, this.wrapFn);
+    this.fired = true;
+    switch (arguments.length) {
+      case 0:
+        return this.listener.call(this.target);
+      case 1:
+        return this.listener.call(this.target, arguments[0]);
+      case 2:
+        return this.listener.call(this.target, arguments[0], arguments[1]);
+      case 3:
+        return this.listener.call(this.target, arguments[0], arguments[1],
+            arguments[2]);
+      default:
+        var args = new Array(arguments.length);
+        for (var i = 0; i < args.length; ++i)
+          args[i] = arguments[i];
+        this.listener.apply(this.target, args);
+    }
+  }
+}
+
+function _onceWrap(target, type, listener) {
+  var state = { fired: false, wrapFn: undefined, target: target, type: type, listener: listener };
+  var wrapped = bind.call(onceWrapper, state);
+  wrapped.listener = listener;
+  state.wrapFn = wrapped;
+  return wrapped;
+}
+
+EventEmitter.prototype.once = function once(type, listener) {
+  if (typeof listener !== 'function')
+    throw new TypeError('"listener" argument must be a function');
+  this.on(type, _onceWrap(this, type, listener));
+  return this;
+};
+
+EventEmitter.prototype.prependOnceListener =
+    function prependOnceListener(type, listener) {
+      if (typeof listener !== 'function')
+        throw new TypeError('"listener" argument must be a function');
+      this.prependListener(type, _onceWrap(this, type, listener));
+      return this;
+    };
+
+// Emits a 'removeListener' event if and only if the listener was removed.
+EventEmitter.prototype.removeListener =
+    function removeListener(type, listener) {
+      var list, events, position, i, originalListener;
+
+      if (typeof listener !== 'function')
+        throw new TypeError('"listener" argument must be a function');
+
+      events = this._events;
+      if (!events)
+        return this;
+
+      list = events[type];
+      if (!list)
+        return this;
+
+      if (list === listener || list.listener === listener) {
+        if (--this._eventsCount === 0)
+          this._events = objectCreate(null);
+        else {
+          delete events[type];
+          if (events.removeListener)
+            this.emit('removeListener', type, list.listener || listener);
+        }
+      } else if (typeof list !== 'function') {
+        position = -1;
+
+        for (i = list.length - 1; i >= 0; i--) {
+          if (list[i] === listener || list[i].listener === listener) {
+            originalListener = list[i].listener;
+            position = i;
+            break;
+          }
+        }
+
+        if (position < 0)
+          return this;
+
+        if (position === 0)
+          list.shift();
+        else
+          spliceOne(list, position);
+
+        if (list.length === 1)
+          events[type] = list[0];
+
+        if (events.removeListener)
+          this.emit('removeListener', type, originalListener || listener);
+      }
+
+      return this;
+    };
+
+EventEmitter.prototype.removeAllListeners =
+    function removeAllListeners(type) {
+      var listeners, events, i;
+
+      events = this._events;
+      if (!events)
+        return this;
+
+      // not listening for removeListener, no need to emit
+      if (!events.removeListener) {
+        if (arguments.length === 0) {
+          this._events = objectCreate(null);
+          this._eventsCount = 0;
+        } else if (events[type]) {
+          if (--this._eventsCount === 0)
+            this._events = objectCreate(null);
+          else
+            delete events[type];
+        }
+        return this;
+      }
+
+      // emit removeListener for all listeners on all events
+      if (arguments.length === 0) {
+        var keys = objectKeys(events);
+        var key;
+        for (i = 0; i < keys.length; ++i) {
+          key = keys[i];
+          if (key === 'removeListener') continue;
+          this.removeAllListeners(key);
+        }
+        this.removeAllListeners('removeListener');
+        this._events = objectCreate(null);
+        this._eventsCount = 0;
+        return this;
+      }
+
+      listeners = events[type];
+
+      if (typeof listeners === 'function') {
+        this.removeListener(type, listeners);
+      } else if (listeners) {
+        // LIFO order
+        for (i = listeners.length - 1; i >= 0; i--) {
+          this.removeListener(type, listeners[i]);
+        }
+      }
+
+      return this;
+    };
+
+function _listeners(target, type, unwrap) {
+  var events = target._events;
+
+  if (!events)
+    return [];
+
+  var evlistener = events[type];
+  if (!evlistener)
+    return [];
+
+  if (typeof evlistener === 'function')
+    return unwrap ? [evlistener.listener || evlistener] : [evlistener];
+
+  return unwrap ? unwrapListeners(evlistener) : arrayClone(evlistener, evlistener.length);
+}
+
+EventEmitter.prototype.listeners = function listeners(type) {
+  return _listeners(this, type, true);
+};
+
+EventEmitter.prototype.rawListeners = function rawListeners(type) {
+  return _listeners(this, type, false);
+};
+
+EventEmitter.listenerCount = function(emitter, type) {
+  if (typeof emitter.listenerCount === 'function') {
+    return emitter.listenerCount(type);
+  } else {
+    return listenerCount.call(emitter, type);
+  }
+};
+
+EventEmitter.prototype.listenerCount = listenerCount;
+function listenerCount(type) {
+  var events = this._events;
+
+  if (events) {
+    var evlistener = events[type];
+
+    if (typeof evlistener === 'function') {
+      return 1;
+    } else if (evlistener) {
+      return evlistener.length;
+    }
+  }
+
+  return 0;
+}
+
+EventEmitter.prototype.eventNames = function eventNames() {
+  return this._eventsCount > 0 ? Reflect.ownKeys(this._events) : [];
+};
+
+// About 1.5x faster than the two-arg version of Array#splice().
+function spliceOne(list, index) {
+  for (var i = index, k = i + 1, n = list.length; k < n; i += 1, k += 1)
+    list[i] = list[k];
+  list.pop();
+}
+
+function arrayClone(arr, n) {
+  var copy = new Array(n);
+  for (var i = 0; i < n; ++i)
+    copy[i] = arr[i];
+  return copy;
+}
+
+function unwrapListeners(arr) {
+  var ret = new Array(arr.length);
+  for (var i = 0; i < ret.length; ++i) {
+    ret[i] = arr[i].listener || arr[i];
+  }
+  return ret;
+}
+
+function objectCreatePolyfill(proto) {
+  var F = function() {};
+  F.prototype = proto;
+  return new F;
+}
+function objectKeysPolyfill(obj) {
+  var keys = [];
+  for (var k in obj) if (Object.prototype.hasOwnProperty.call(obj, k)) {
+    keys.push(k);
+  }
+  return k;
+}
+function functionBindPolyfill(context) {
+  var fn = this;
+  return function () {
+    return fn.apply(context, arguments);
+  };
+}
+
+},{}],3:[function(_dereq_,module,exports){
+(function (global){
+'use strict';
+var Mutation = global.MutationObserver || global.WebKitMutationObserver;
+
+var scheduleDrain;
+
+{
+  if (Mutation) {
+    var called = 0;
+    var observer = new Mutation(nextTick);
+    var element = global.document.createTextNode('');
+    observer.observe(element, {
+      characterData: true
+    });
+    scheduleDrain = function () {
+      element.data = (called = ++called % 2);
+    };
+  } else if (!global.setImmediate && typeof global.MessageChannel !== 'undefined') {
+    var channel = new global.MessageChannel();
+    channel.port1.onmessage = nextTick;
+    scheduleDrain = function () {
+      channel.port2.postMessage(0);
+    };
+  } else if ('document' in global && 'onreadystatechange' in global.document.createElement('script')) {
+    scheduleDrain = function () {
+
+      // Create a <script> element; its readystatechange event will be fired asynchronously once it is inserted
+      // into the document. Do so, thus queuing up the task. Remember to clean up once it's been called.
+      var scriptEl = global.document.createElement('script');
+      scriptEl.onreadystatechange = function () {
+        nextTick();
+
+        scriptEl.onreadystatechange = null;
+        scriptEl.parentNode.removeChild(scriptEl);
+        scriptEl = null;
+      };
+      global.document.documentElement.appendChild(scriptEl);
+    };
+  } else {
+    scheduleDrain = function () {
+      setTimeout(nextTick, 0);
+    };
+  }
+}
+
+var draining;
+var queue = [];
+//named nextTick for less confusing stack traces
+function nextTick() {
+  draining = true;
+  var i, oldQueue;
+  var len = queue.length;
+  while (len) {
+    oldQueue = queue;
+    queue = [];
+    i = -1;
+    while (++i < len) {
+      oldQueue[i]();
+    }
+    len = queue.length;
+  }
+  draining = false;
+}
+
+module.exports = immediate;
+function immediate(task) {
+  if (queue.push(task) === 1 && !draining) {
+    scheduleDrain();
+  }
+}
+
+}).call(this,typeof global !== "undefined" ? global : typeof self !== "undefined" ? self : typeof window !== "undefined" ? window : {})
+},{}],4:[function(_dereq_,module,exports){
+if (typeof Object.create === 'function') {
+  // implementation from standard node.js 'util' module
+  module.exports = function inherits(ctor, superCtor) {
+    ctor.super_ = superCtor
+    ctor.prototype = Object.create(superCtor.prototype, {
+      constructor: {
+        value: ctor,
+        enumerable: false,
+        writable: true,
+        configurable: true
+      }
+    });
+  };
+} else {
+  // old school shim for old browsers
+  module.exports = function inherits(ctor, superCtor) {
+    ctor.super_ = superCtor
+    var TempCtor = function () {}
+    TempCtor.prototype = superCtor.prototype
+    ctor.prototype = new TempCtor()
+    ctor.prototype.constructor = ctor
+  }
+}
+
+},{}],5:[function(_dereq_,module,exports){
+// shim for using process in browser
+var process = module.exports = {};
+
+// cached from whatever global is present so that test runners that stub it
+// don't break things.  But we need to wrap it in a try catch in case it is
+// wrapped in strict mode code which doesn't define any globals.  It's inside a
+// function because try/catches deoptimize in certain engines.
+
+var cachedSetTimeout;
+var cachedClearTimeout;
+
+function defaultSetTimout() {
+    throw new Error('setTimeout has not been defined');
+}
+function defaultClearTimeout () {
+    throw new Error('clearTimeout has not been defined');
+}
+(function () {
+    try {
+        if (typeof setTimeout === 'function') {
+            cachedSetTimeout = setTimeout;
+        } else {
+            cachedSetTimeout = defaultSetTimout;
+        }
+    } catch (e) {
+        cachedSetTimeout = defaultSetTimout;
+    }
+    try {
+        if (typeof clearTimeout === 'function') {
+            cachedClearTimeout = clearTimeout;
+        } else {
+            cachedClearTimeout = defaultClearTimeout;
+        }
+    } catch (e) {
+        cachedClearTimeout = defaultClearTimeout;
+    }
+} ())
+function runTimeout(fun) {
+    if (cachedSetTimeout === setTimeout) {
+        //normal enviroments in sane situations
+        return setTimeout(fun, 0);
+    }
+    // if setTimeout wasn't available but was latter defined
+    if ((cachedSetTimeout === defaultSetTimout || !cachedSetTimeout) && setTimeout) {
+        cachedSetTimeout = setTimeout;
+        return setTimeout(fun, 0);
+    }
+    try {
+        // when when somebody has screwed with setTimeout but no I.E. maddness
+        return cachedSetTimeout(fun, 0);
+    } catch(e){
+        try {
+            // When we are in I.E. but the script has been evaled so I.E. doesn't trust the global object when called normally
+            return cachedSetTimeout.call(null, fun, 0);
+        } catch(e){
+            // same as above but when it's a version of I.E. that must have the global object for 'this', hopfully our context correct otherwise it will throw a global error
+            return cachedSetTimeout.call(this, fun, 0);
+        }
+    }
+
+
+}
+function runClearTimeout(marker) {
+    if (cachedClearTimeout === clearTimeout) {
+        //normal enviroments in sane situations
+        return clearTimeout(marker);
+    }
+    // if clearTimeout wasn't available but was latter defined
+    if ((cachedClearTimeout === defaultClearTimeout || !cachedClearTimeout) && clearTimeout) {
+        cachedClearTimeout = clearTimeout;
+        return clearTimeout(marker);
+    }
+    try {
+        // when when somebody has screwed with setTimeout but no I.E. maddness
+        return cachedClearTimeout(marker);
+    } catch (e){
+        try {
+            // When we are in I.E. but the script has been evaled so I.E. doesn't  trust the global object when called normally
+            return cachedClearTimeout.call(null, marker);
+        } catch (e){
+            // same as above but when it's a version of I.E. that must have the global object for 'this', hopfully our context correct otherwise it will throw a global error.
+            // Some versions of I.E. have different rules for clearTimeout vs setTimeout
+            return cachedClearTimeout.call(this, marker);
+        }
+    }
+
+
+
+}
+var queue = [];
+var draining = false;
+var currentQueue;
+var queueIndex = -1;
+
+function cleanUpNextTick() {
+    if (!draining || !currentQueue) {
+        return;
+    }
+    draining = false;
+    if (currentQueue.length) {
+        queue = currentQueue.concat(queue);
+    } else {
+        queueIndex = -1;
+    }
+    if (queue.length) {
+        drainQueue();
+    }
+}
+
+function drainQueue() {
+    if (draining) {
+        return;
+    }
+    var timeout = runTimeout(cleanUpNextTick);
+    draining = true;
+
+    var len = queue.length;
+    while(len) {
+        currentQueue = queue;
+        queue = [];
+        while (++queueIndex < len) {
+            if (currentQueue) {
+                currentQueue[queueIndex].run();
+            }
+        }
+        queueIndex = -1;
+        len = queue.length;
+    }
+    currentQueue = null;
+    draining = false;
+    runClearTimeout(timeout);
+}
+
+process.nextTick = function (fun) {
+    var args = new Array(arguments.length - 1);
+    if (arguments.length > 1) {
+        for (var i = 1; i < arguments.length; i++) {
+            args[i - 1] = arguments[i];
+        }
+    }
+    queue.push(new Item(fun, args));
+    if (queue.length === 1 && !draining) {
+        runTimeout(drainQueue);
+    }
+};
+
+// v8 likes predictible objects
+function Item(fun, array) {
+    this.fun = fun;
+    this.array = array;
+}
+Item.prototype.run = function () {
+    this.fun.apply(null, this.array);
+};
+process.title = 'browser';
+process.browser = true;
+process.env = {};
+process.argv = [];
+process.version = ''; // empty string to avoid regexp issues
+process.versions = {};
+
+function noop() {}
+
+process.on = noop;
+process.addListener = noop;
+process.once = noop;
+process.off = noop;
+process.removeListener = noop;
+process.removeAllListeners = noop;
+process.emit = noop;
+process.prependListener = noop;
+process.prependOnceListener = noop;
+
+process.listeners = function (name) { return [] }
+
+process.binding = function (name) {
+    throw new Error('process.binding is not supported');
+};
+
+process.cwd = function () { return '/' };
+process.chdir = function (dir) {
+    throw new Error('process.chdir is not supported');
+};
+process.umask = function() { return 0; };
+
+},{}],6:[function(_dereq_,module,exports){
+(function (factory) {
+    if (typeof exports === 'object') {
+        // Node/CommonJS
+        module.exports = factory();
+    } else if (typeof define === 'function' && define.amd) {
+        // AMD
+        define(factory);
+    } else {
+        // Browser globals (with support for web workers)
+        var glob;
+
+        try {
+            glob = window;
+        } catch (e) {
+            glob = self;
+        }
+
+        glob.SparkMD5 = factory();
+    }
+}(function (undefined) {
+
+    'use strict';
+
+    /*
+     * Fastest md5 implementation around (JKM md5).
+     * Credits: Joseph Myers
+     *
+     * @see http://www.myersdaily.org/joseph/javascript/md5-text.html
+     * @see http://jsperf.com/md5-shootout/7
+     */
+
+    /* this function is much faster,
+      so if possible we use it. Some IEs
+      are the only ones I know of that
+      need the idiotic second function,
+      generated by an if clause.  */
+    var add32 = function (a, b) {
+        return (a + b) & 0xFFFFFFFF;
+    },
+        hex_chr = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'];
+
+
+    function cmn(q, a, b, x, s, t) {
+        a = add32(add32(a, q), add32(x, t));
+        return add32((a << s) | (a >>> (32 - s)), b);
+    }
+
+    function md5cycle(x, k) {
+        var a = x[0],
+            b = x[1],
+            c = x[2],
+            d = x[3];
+
+        a += (b & c | ~b & d) + k[0] - 680876936 | 0;
+        a  = (a << 7 | a >>> 25) + b | 0;
+        d += (a & b | ~a & c) + k[1] - 389564586 | 0;
+        d  = (d << 12 | d >>> 20) + a | 0;
+        c += (d & a | ~d & b) + k[2] + 606105819 | 0;
+        c  = (c << 17 | c >>> 15) + d | 0;
+        b += (c & d | ~c & a) + k[3] - 1044525330 | 0;
+        b  = (b << 22 | b >>> 10) + c | 0;
+        a += (b & c | ~b & d) + k[4] - 176418897 | 0;
+        a  = (a << 7 | a >>> 25) + b | 0;
+        d += (a & b | ~a & c) + k[5] + 1200080426 | 0;
+        d  = (d << 12 | d >>> 20) + a | 0;
+        c += (d & a | ~d & b) + k[6] - 1473231341 | 0;
+        c  = (c << 17 | c >>> 15) + d | 0;
+        b += (c & d | ~c & a) + k[7] - 45705983 | 0;
+        b  = (b << 22 | b >>> 10) + c | 0;
+        a += (b & c | ~b & d) + k[8] + 1770035416 | 0;
+        a  = (a << 7 | a >>> 25) + b | 0;
+        d += (a & b | ~a & c) + k[9] - 1958414417 | 0;
+        d  = (d << 12 | d >>> 20) + a | 0;
+        c += (d & a | ~d & b) + k[10] - 42063 | 0;
+        c  = (c << 17 | c >>> 15) + d | 0;
+        b += (c & d | ~c & a) + k[11] - 1990404162 | 0;
+        b  = (b << 22 | b >>> 10) + c | 0;
+        a += (b & c | ~b & d) + k[12] + 1804603682 | 0;
+        a  = (a << 7 | a >>> 25) + b | 0;
+        d += (a & b | ~a & c) + k[13] - 40341101 | 0;
+        d  = (d << 12 | d >>> 20) + a | 0;
+        c += (d & a | ~d & b) + k[14] - 1502002290 | 0;
+        c  = (c << 17 | c >>> 15) + d | 0;
+        b += (c & d | ~c & a) + k[15] + 1236535329 | 0;
+        b  = (b << 22 | b >>> 10) + c | 0;
+
+        a += (b & d | c & ~d) + k[1] - 165796510 | 0;
+        a  = (a << 5 | a >>> 27) + b | 0;
+        d += (a & c | b & ~c) + k[6] - 1069501632 | 0;
+        d  = (d << 9 | d >>> 23) + a | 0;
+        c += (d & b | a & ~b) + k[11] + 643717713 | 0;
+        c  = (c << 14 | c >>> 18) + d | 0;
+        b += (c & a | d & ~a) + k[0] - 373897302 | 0;
+        b  = (b << 20 | b >>> 12) + c | 0;
+        a += (b & d | c & ~d) + k[5] - 701558691 | 0;
+        a  = (a << 5 | a >>> 27) + b | 0;
+        d += (a & c | b & ~c) + k[10] + 38016083 | 0;
+        d  = (d << 9 | d >>> 23) + a | 0;
+        c += (d & b | a & ~b) + k[15] - 660478335 | 0;
+        c  = (c << 14 | c >>> 18) + d | 0;
+        b += (c & a | d & ~a) + k[4] - 405537848 | 0;
+        b  = (b << 20 | b >>> 12) + c | 0;
+        a += (b & d | c & ~d) + k[9] + 568446438 | 0;
+        a  = (a << 5 | a >>> 27) + b | 0;
+        d += (a & c | b & ~c) + k[14] - 1019803690 | 0;
+        d  = (d << 9 | d >>> 23) + a | 0;
+        c += (d & b | a & ~b) + k[3] - 187363961 | 0;
+        c  = (c << 14 | c >>> 18) + d | 0;
+        b += (c & a | d & ~a) + k[8] + 1163531501 | 0;
+        b  = (b << 20 | b >>> 12) + c | 0;
+        a += (b & d | c & ~d) + k[13] - 1444681467 | 0;
+        a  = (a << 5 | a >>> 27) + b | 0;
+        d += (a & c | b & ~c) + k[2] - 51403784 | 0;
+        d  = (d << 9 | d >>> 23) + a | 0;
+        c += (d & b | a & ~b) + k[7] + 1735328473 | 0;
+        c  = (c << 14 | c >>> 18) + d | 0;
+        b += (c & a | d & ~a) + k[12] - 1926607734 | 0;
+        b  = (b << 20 | b >>> 12) + c | 0;
+
+        a += (b ^ c ^ d) + k[5] - 378558 | 0;
+        a  = (a << 4 | a >>> 28) + b | 0;
+        d += (a ^ b ^ c) + k[8] - 2022574463 | 0;
+        d  = (d << 11 | d >>> 21) + a | 0;
+        c += (d ^ a ^ b) + k[11] + 1839030562 | 0;
+        c  = (c << 16 | c >>> 16) + d | 0;
+        b += (c ^ d ^ a) + k[14] - 35309556 | 0;
+        b  = (b << 23 | b >>> 9) + c | 0;
+        a += (b ^ c ^ d) + k[1] - 1530992060 | 0;
+        a  = (a << 4 | a >>> 28) + b | 0;
+        d += (a ^ b ^ c) + k[4] + 1272893353 | 0;
+        d  = (d << 11 | d >>> 21) + a | 0;
+        c += (d ^ a ^ b) + k[7] - 155497632 | 0;
+        c  = (c << 16 | c >>> 16) + d | 0;
+        b += (c ^ d ^ a) + k[10] - 1094730640 | 0;
+        b  = (b << 23 | b >>> 9) + c | 0;
+        a += (b ^ c ^ d) + k[13] + 681279174 | 0;
+        a  = (a << 4 | a >>> 28) + b | 0;
+        d += (a ^ b ^ c) + k[0] - 358537222 | 0;
+        d  = (d << 11 | d >>> 21) + a | 0;
+        c += (d ^ a ^ b) + k[3] - 722521979 | 0;
+        c  = (c << 16 | c >>> 16) + d | 0;
+        b += (c ^ d ^ a) + k[6] + 76029189 | 0;
+        b  = (b << 23 | b >>> 9) + c | 0;
+        a += (b ^ c ^ d) + k[9] - 640364487 | 0;
+        a  = (a << 4 | a >>> 28) + b | 0;
+        d += (a ^ b ^ c) + k[12] - 421815835 | 0;
+        d  = (d << 11 | d >>> 21) + a | 0;
+        c += (d ^ a ^ b) + k[15] + 530742520 | 0;
+        c  = (c << 16 | c >>> 16) + d | 0;
+        b += (c ^ d ^ a) + k[2] - 995338651 | 0;
+        b  = (b << 23 | b >>> 9) + c | 0;
+
+        a += (c ^ (b | ~d)) + k[0] - 198630844 | 0;
+        a  = (a << 6 | a >>> 26) + b | 0;
+        d += (b ^ (a | ~c)) + k[7] + 1126891415 | 0;
+        d  = (d << 10 | d >>> 22) + a | 0;
+        c += (a ^ (d | ~b)) + k[14] - 1416354905 | 0;
+        c  = (c << 15 | c >>> 17) + d | 0;
+        b += (d ^ (c | ~a)) + k[5] - 57434055 | 0;
+        b  = (b << 21 |b >>> 11) + c | 0;
+        a += (c ^ (b | ~d)) + k[12] + 1700485571 | 0;
+        a  = (a << 6 | a >>> 26) + b | 0;
+        d += (b ^ (a | ~c)) + k[3] - 1894986606 | 0;
+        d  = (d << 10 | d >>> 22) + a | 0;
+        c += (a ^ (d | ~b)) + k[10] - 1051523 | 0;
+        c  = (c << 15 | c >>> 17) + d | 0;
+        b += (d ^ (c | ~a)) + k[1] - 2054922799 | 0;
+        b  = (b << 21 |b >>> 11) + c | 0;
+        a += (c ^ (b | ~d)) + k[8] + 1873313359 | 0;
+        a  = (a << 6 | a >>> 26) + b | 0;
+        d += (b ^ (a | ~c)) + k[15] - 30611744 | 0;
+        d  = (d << 10 | d >>> 22) + a | 0;
+        c += (a ^ (d | ~b)) + k[6] - 1560198380 | 0;
+        c  = (c << 15 | c >>> 17) + d | 0;
+        b += (d ^ (c | ~a)) + k[13] + 1309151649 | 0;
+        b  = (b << 21 |b >>> 11) + c | 0;
+        a += (c ^ (b | ~d)) + k[4] - 145523070 | 0;
+        a  = (a << 6 | a >>> 26) + b | 0;
+        d += (b ^ (a | ~c)) + k[11] - 1120210379 | 0;
+        d  = (d << 10 | d >>> 22) + a | 0;
+        c += (a ^ (d | ~b)) + k[2] + 718787259 | 0;
+        c  = (c << 15 | c >>> 17) + d | 0;
+        b += (d ^ (c | ~a)) + k[9] - 343485551 | 0;
+        b  = (b << 21 | b >>> 11) + c | 0;
+
+        x[0] = a + x[0] | 0;
+        x[1] = b + x[1] | 0;
+        x[2] = c + x[2] | 0;
+        x[3] = d + x[3] | 0;
+    }
+
+    function md5blk(s) {
+        var md5blks = [],
+            i; /* Andy King said do it this way. */
+
+        for (i = 0; i < 64; i += 4) {
+            md5blks[i >> 2] = s.charCodeAt(i) + (s.charCodeAt(i + 1) << 8) + (s.charCodeAt(i + 2) << 16) + (s.charCodeAt(i + 3) << 24);
+        }
+        return md5blks;
+    }
+
+    function md5blk_array(a) {
+        var md5blks = [],
+            i; /* Andy King said do it this way. */
+
+        for (i = 0; i < 64; i += 4) {
+            md5blks[i >> 2] = a[i] + (a[i + 1] << 8) + (a[i + 2] << 16) + (a[i + 3] << 24);
+        }
+        return md5blks;
+    }
+
+    function md51(s) {
+        var n = s.length,
+            state = [1732584193, -271733879, -1732584194, 271733878],
+            i,
+            length,
+            tail,
+            tmp,
+            lo,
+            hi;
+
+        for (i = 64; i <= n; i += 64) {
+            md5cycle(state, md5blk(s.substring(i - 64, i)));
+        }
+        s = s.substring(i - 64);
+        length = s.length;
+        tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+        for (i = 0; i < length; i += 1) {
+            tail[i >> 2] |= s.charCodeAt(i) << ((i % 4) << 3);
+        }
+        tail[i >> 2] |= 0x80 << ((i % 4) << 3);
+        if (i > 55) {
+            md5cycle(state, tail);
+            for (i = 0; i < 16; i += 1) {
+                tail[i] = 0;
+            }
+        }
+
+        // Beware that the final length might not fit in 32 bits so we take care of that
+        tmp = n * 8;
+        tmp = tmp.toString(16).match(/(.*?)(.{0,8})$/);
+        lo = parseInt(tmp[2], 16);
+        hi = parseInt(tmp[1], 16) || 0;
+
+        tail[14] = lo;
+        tail[15] = hi;
+
+        md5cycle(state, tail);
+        return state;
+    }
+
+    function md51_array(a) {
+        var n = a.length,
+            state = [1732584193, -271733879, -1732584194, 271733878],
+            i,
+            length,
+            tail,
+            tmp,
+            lo,
+            hi;
+
+        for (i = 64; i <= n; i += 64) {
+            md5cycle(state, md5blk_array(a.subarray(i - 64, i)));
+        }
+
+        // Not sure if it is a bug, however IE10 will always produce a sub array of length 1
+        // containing the last element of the parent array if the sub array specified starts
+        // beyond the length of the parent array - weird.
+        // https://connect.microsoft.com/IE/feedback/details/771452/typed-array-subarray-issue
+        a = (i - 64) < n ? a.subarray(i - 64) : new Uint8Array(0);
+
+        length = a.length;
+        tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+        for (i = 0; i < length; i += 1) {
+            tail[i >> 2] |= a[i] << ((i % 4) << 3);
+        }
+
+        tail[i >> 2] |= 0x80 << ((i % 4) << 3);
+        if (i > 55) {
+            md5cycle(state, tail);
+            for (i = 0; i < 16; i += 1) {
+                tail[i] = 0;
+            }
+        }
+
+        // Beware that the final length might not fit in 32 bits so we take care of that
+        tmp = n * 8;
+        tmp = tmp.toString(16).match(/(.*?)(.{0,8})$/);
+        lo = parseInt(tmp[2], 16);
+        hi = parseInt(tmp[1], 16) || 0;
+
+        tail[14] = lo;
+        tail[15] = hi;
+
+        md5cycle(state, tail);
+
+        return state;
+    }
+
+    function rhex(n) {
+        var s = '',
+            j;
+        for (j = 0; j < 4; j += 1) {
+            s += hex_chr[(n >> (j * 8 + 4)) & 0x0F] + hex_chr[(n >> (j * 8)) & 0x0F];
+        }
+        return s;
+    }
+
+    function hex(x) {
+        var i;
+        for (i = 0; i < x.length; i += 1) {
+            x[i] = rhex(x[i]);
+        }
+        return x.join('');
+    }
+
+    // In some cases the fast add32 function cannot be used..
+    if (hex(md51('hello')) !== '5d41402abc4b2a76b9719d911017c592') {
+        add32 = function (x, y) {
+            var lsw = (x & 0xFFFF) + (y & 0xFFFF),
+                msw = (x >> 16) + (y >> 16) + (lsw >> 16);
+            return (msw << 16) | (lsw & 0xFFFF);
+        };
+    }
+
+    // ---------------------------------------------------
+
+    /**
+     * ArrayBuffer slice polyfill.
+     *
+     * @see https://github.com/ttaubert/node-arraybuffer-slice
+     */
+
+    if (typeof ArrayBuffer !== 'undefined' && !ArrayBuffer.prototype.slice) {
+        (function () {
+            function clamp(val, length) {
+                val = (val | 0) || 0;
+
+                if (val < 0) {
+                    return Math.max(val + length, 0);
+                }
+
+                return Math.min(val, length);
+            }
+
+            ArrayBuffer.prototype.slice = function (from, to) {
+                var length = this.byteLength,
+                    begin = clamp(from, length),
+                    end = length,
+                    num,
+                    target,
+                    targetArray,
+                    sourceArray;
+
+                if (to !== undefined) {
+                    end = clamp(to, length);
+                }
+
+                if (begin > end) {
+                    return new ArrayBuffer(0);
+                }
+
+                num = end - begin;
+                target = new ArrayBuffer(num);
+                targetArray = new Uint8Array(target);
+
+                sourceArray = new Uint8Array(this, begin, num);
+                targetArray.set(sourceArray);
+
+                return target;
+            };
+        })();
+    }
+
+    // ---------------------------------------------------
+
+    /**
+     * Helpers.
+     */
+
+    function toUtf8(str) {
+        if (/[\u0080-\uFFFF]/.test(str)) {
+            str = unescape(encodeURIComponent(str));
+        }
+
+        return str;
+    }
+
+    function utf8Str2ArrayBuffer(str, returnUInt8Array) {
+        var length = str.length,
+           buff = new ArrayBuffer(length),
+           arr = new Uint8Array(buff),
+           i;
+
+        for (i = 0; i < length; i += 1) {
+            arr[i] = str.charCodeAt(i);
+        }
+
+        return returnUInt8Array ? arr : buff;
+    }
+
+    function arrayBuffer2Utf8Str(buff) {
+        return String.fromCharCode.apply(null, new Uint8Array(buff));
+    }
+
+    function concatenateArrayBuffers(first, second, returnUInt8Array) {
+        var result = new Uint8Array(first.byteLength + second.byteLength);
+
+        result.set(new Uint8Array(first));
+        result.set(new Uint8Array(second), first.byteLength);
+
+        return returnUInt8Array ? result : result.buffer;
+    }
+
+    function hexToBinaryString(hex) {
+        var bytes = [],
+            length = hex.length,
+            x;
+
+        for (x = 0; x < length - 1; x += 2) {
+            bytes.push(parseInt(hex.substr(x, 2), 16));
+        }
+
+        return String.fromCharCode.apply(String, bytes);
+    }
+
+    // ---------------------------------------------------
+
+    /**
+     * SparkMD5 OOP implementation.
+     *
+     * Use this class to perform an incremental md5, otherwise use the
+     * static methods instead.
+     */
+
+    function SparkMD5() {
+        // call reset to init the instance
+        this.reset();
+    }
+
+    /**
+     * Appends a string.
+     * A conversion will be applied if an utf8 string is detected.
+     *
+     * @param {String} str The string to be appended
+     *
+     * @return {SparkMD5} The instance itself
+     */
+    SparkMD5.prototype.append = function (str) {
+        // Converts the string to utf8 bytes if necessary
+        // Then append as binary
+        this.appendBinary(toUtf8(str));
+
+        return this;
+    };
+
+    /**
+     * Appends a binary string.
+     *
+     * @param {String} contents The binary string to be appended
+     *
+     * @return {SparkMD5} The instance itself
+     */
+    SparkMD5.prototype.appendBinary = function (contents) {
+        this._buff += contents;
+        this._length += contents.length;
+
+        var length = this._buff.length,
+            i;
+
+        for (i = 64; i <= length; i += 64) {
+            md5cycle(this._hash, md5blk(this._buff.substring(i - 64, i)));
+        }
+
+        this._buff = this._buff.substring(i - 64);
+
+        return this;
+    };
+
+    /**
+     * Finishes the incremental computation, reseting the internal state and
+     * returning the result.
+     *
+     * @param {Boolean} raw True to get the raw string, false to get the hex string
+     *
+     * @return {String} The result
+     */
+    SparkMD5.prototype.end = function (raw) {
+        var buff = this._buff,
+            length = buff.length,
+            i,
+            tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+            ret;
+
+        for (i = 0; i < length; i += 1) {
+            tail[i >> 2] |= buff.charCodeAt(i) << ((i % 4) << 3);
+        }
+
+        this._finish(tail, length);
+        ret = hex(this._hash);
+
+        if (raw) {
+            ret = hexToBinaryString(ret);
+        }
+
+        this.reset();
+
+        return ret;
+    };
+
+    /**
+     * Resets the internal state of the computation.
+     *
+     * @return {SparkMD5} The instance itself
+     */
+    SparkMD5.prototype.reset = function () {
+        this._buff = '';
+        this._length = 0;
+        this._hash = [1732584193, -271733879, -1732584194, 271733878];
+
+        return this;
+    };
+
+    /**
+     * Gets the internal state of the computation.
+     *
+     * @return {Object} The state
+     */
+    SparkMD5.prototype.getState = function () {
+        return {
+            buff: this._buff,
+            length: this._length,
+            hash: this._hash
+        };
+    };
+
+    /**
+     * Gets the internal state of the computation.
+     *
+     * @param {Object} state The state
+     *
+     * @return {SparkMD5} The instance itself
+     */
+    SparkMD5.prototype.setState = function (state) {
+        this._buff = state.buff;
+        this._length = state.length;
+        this._hash = state.hash;
+
+        return this;
+    };
+
+    /**
+     * Releases memory used by the incremental buffer and other additional
+     * resources. If you plan to use the instance again, use reset instead.
+     */
+    SparkMD5.prototype.destroy = function () {
+        delete this._hash;
+        delete this._buff;
+        delete this._length;
+    };
+
+    /**
+     * Finish the final calculation based on the tail.
+     *
+     * @param {Array}  tail   The tail (will be modified)
+     * @param {Number} length The length of the remaining buffer
+     */
+    SparkMD5.prototype._finish = function (tail, length) {
+        var i = length,
+            tmp,
+            lo,
+            hi;
+
+        tail[i >> 2] |= 0x80 << ((i % 4) << 3);
+        if (i > 55) {
+            md5cycle(this._hash, tail);
+            for (i = 0; i < 16; i += 1) {
+                tail[i] = 0;
+            }
+        }
+
+        // Do the final computation based on the tail and length
+        // Beware that the final length may not fit in 32 bits so we take care of that
+        tmp = this._length * 8;
+        tmp = tmp.toString(16).match(/(.*?)(.{0,8})$/);
+        lo = parseInt(tmp[2], 16);
+        hi = parseInt(tmp[1], 16) || 0;
+
+        tail[14] = lo;
+        tail[15] = hi;
+        md5cycle(this._hash, tail);
+    };
+
+    /**
+     * Performs the md5 hash on a string.
+     * A conversion will be applied if utf8 string is detected.
+     *
+     * @param {String}  str The string
+     * @param {Boolean} raw True to get the raw string, false to get the hex string
+     *
+     * @return {String} The result
+     */
+    SparkMD5.hash = function (str, raw) {
+        // Converts the string to utf8 bytes if necessary
+        // Then compute it using the binary function
+        return SparkMD5.hashBinary(toUtf8(str), raw);
+    };
+
+    /**
+     * Performs the md5 hash on a binary string.
+     *
+     * @param {String}  content The binary string
+     * @param {Boolean} raw     True to get the raw string, false to get the hex string
+     *
+     * @return {String} The result
+     */
+    SparkMD5.hashBinary = function (content, raw) {
+        var hash = md51(content),
+            ret = hex(hash);
+
+        return raw ? hexToBinaryString(ret) : ret;
+    };
+
+    // ---------------------------------------------------
+
+    /**
+     * SparkMD5 OOP implementation for array buffers.
+     *
+     * Use this class to perform an incremental md5 ONLY for array buffers.
+     */
+    SparkMD5.ArrayBuffer = function () {
+        // call reset to init the instance
+        this.reset();
+    };
+
+    /**
+     * Appends an array buffer.
+     *
+     * @param {ArrayBuffer} arr The array to be appended
+     *
+     * @return {SparkMD5.ArrayBuffer} The instance itself
+     */
+    SparkMD5.ArrayBuffer.prototype.append = function (arr) {
+        var buff = concatenateArrayBuffers(this._buff.buffer, arr, true),
+            length = buff.length,
+            i;
+
+        this._length += arr.byteLength;
+
+        for (i = 64; i <= length; i += 64) {
+            md5cycle(this._hash, md5blk_array(buff.subarray(i - 64, i)));
+        }
+
+        this._buff = (i - 64) < length ? new Uint8Array(buff.buffer.slice(i - 64)) : new Uint8Array(0);
+
+        return this;
+    };
+
+    /**
+     * Finishes the incremental computation, reseting the internal state and
+     * returning the result.
+     *
+     * @param {Boolean} raw True to get the raw string, false to get the hex string
+     *
+     * @return {String} The result
+     */
+    SparkMD5.ArrayBuffer.prototype.end = function (raw) {
+        var buff = this._buff,
+            length = buff.length,
+            tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+            i,
+            ret;
+
+        for (i = 0; i < length; i += 1) {
+            tail[i >> 2] |= buff[i] << ((i % 4) << 3);
+        }
+
+        this._finish(tail, length);
+        ret = hex(this._hash);
+
+        if (raw) {
+            ret = hexToBinaryString(ret);
+        }
+
+        this.reset();
+
+        return ret;
+    };
+
+    /**
+     * Resets the internal state of the computation.
+     *
+     * @return {SparkMD5.ArrayBuffer} The instance itself
+     */
+    SparkMD5.ArrayBuffer.prototype.reset = function () {
+        this._buff = new Uint8Array(0);
+        this._length = 0;
+        this._hash = [1732584193, -271733879, -1732584194, 271733878];
+
+        return this;
+    };
+
+    /**
+     * Gets the internal state of the computation.
+     *
+     * @return {Object} The state
+     */
+    SparkMD5.ArrayBuffer.prototype.getState = function () {
+        var state = SparkMD5.prototype.getState.call(this);
+
+        // Convert buffer to a string
+        state.buff = arrayBuffer2Utf8Str(state.buff);
+
+        return state;
+    };
+
+    /**
+     * Gets the internal state of the computation.
+     *
+     * @param {Object} state The state
+     *
+     * @return {SparkMD5.ArrayBuffer} The instance itself
+     */
+    SparkMD5.ArrayBuffer.prototype.setState = function (state) {
+        // Convert string to buffer
+        state.buff = utf8Str2ArrayBuffer(state.buff, true);
+
+        return SparkMD5.prototype.setState.call(this, state);
+    };
+
+    SparkMD5.ArrayBuffer.prototype.destroy = SparkMD5.prototype.destroy;
+
+    SparkMD5.ArrayBuffer.prototype._finish = SparkMD5.prototype._finish;
+
+    /**
+     * Performs the md5 hash on an array buffer.
+     *
+     * @param {ArrayBuffer} arr The array buffer
+     * @param {Boolean}     raw True to get the raw string, false to get the hex one
+     *
+     * @return {String} The result
+     */
+    SparkMD5.ArrayBuffer.hash = function (arr, raw) {
+        var hash = md51_array(new Uint8Array(arr)),
+            ret = hex(hash);
+
+        return raw ? hexToBinaryString(ret) : ret;
+    };
+
+    return SparkMD5;
+}));
+
+},{}],7:[function(_dereq_,module,exports){
+var v1 = _dereq_(10);
+var v4 = _dereq_(11);
+
+var uuid = v4;
+uuid.v1 = v1;
+uuid.v4 = v4;
+
+module.exports = uuid;
+
+},{"10":10,"11":11}],8:[function(_dereq_,module,exports){
+/**
+ * Convert array of 16 byte values to UUID string format of the form:
+ * XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
+ */
+var byteToHex = [];
+for (var i = 0; i < 256; ++i) {
+  byteToHex[i] = (i + 0x100).toString(16).substr(1);
+}
+
+function bytesToUuid(buf, offset) {
+  var i = offset || 0;
+  var bth = byteToHex;
+  return bth[buf[i++]] + bth[buf[i++]] +
+          bth[buf[i++]] + bth[buf[i++]] + '-' +
+          bth[buf[i++]] + bth[buf[i++]] + '-' +
+          bth[buf[i++]] + bth[buf[i++]] + '-' +
+          bth[buf[i++]] + bth[buf[i++]] + '-' +
+          bth[buf[i++]] + bth[buf[i++]] +
+          bth[buf[i++]] + bth[buf[i++]] +
+          bth[buf[i++]] + bth[buf[i++]];
+}
+
+module.exports = bytesToUuid;
+
+},{}],9:[function(_dereq_,module,exports){
+// Unique ID creation requires a high quality random # generator.  In the
+// browser this is a little complicated due to unknown quality of Math.random()
+// and inconsistent support for the `crypto` API.  We do the best we can via
+// feature-detection
+
+// getRandomValues needs to be invoked in a context where "this" is a Crypto implementation.
+var getRandomValues = (typeof(crypto) != 'undefined' && crypto.getRandomValues.bind(crypto)) ||
+                      (typeof(msCrypto) != 'undefined' && msCrypto.getRandomValues.bind(msCrypto));
+if (getRandomValues) {
+  // WHATWG crypto RNG - http://wiki.whatwg.org/wiki/Crypto
+  var rnds8 = new Uint8Array(16); // eslint-disable-line no-undef
+
+  module.exports = function whatwgRNG() {
+    getRandomValues(rnds8);
+    return rnds8;
+  };
+} else {
+  // Math.random()-based (RNG)
+  //
+  // If all else fails, use Math.random().  It's fast, but is of unspecified
+  // quality.
+  var rnds = new Array(16);
+
+  module.exports = function mathRNG() {
+    for (var i = 0, r; i < 16; i++) {
+      if ((i & 0x03) === 0) r = Math.random() * 0x100000000;
+      rnds[i] = r >>> ((i & 0x03) << 3) & 0xff;
+    }
+
+    return rnds;
+  };
+}
+
+},{}],10:[function(_dereq_,module,exports){
+var rng = _dereq_(9);
+var bytesToUuid = _dereq_(8);
+
+// **`v1()` - Generate time-based UUID**
+//
+// Inspired by https://github.com/LiosK/UUID.js
+// and http://docs.python.org/library/uuid.html
+
+var _nodeId;
+var _clockseq;
+
+// Previous uuid creation time
+var _lastMSecs = 0;
+var _lastNSecs = 0;
+
+// See https://github.com/broofa/node-uuid for API details
+function v1(options, buf, offset) {
+  var i = buf && offset || 0;
+  var b = buf || [];
+
+  options = options || {};
+  var node = options.node || _nodeId;
+  var clockseq = options.clockseq !== undefined ? options.clockseq : _clockseq;
+
+  // node and clockseq need to be initialized to random values if they're not
+  // specified.  We do this lazily to minimize issues related to insufficient
+  // system entropy.  See #189
+  if (node == null || clockseq == null) {
+    var seedBytes = rng();
+    if (node == null) {
+      // Per 4.5, create and 48-bit node id, (47 random bits + multicast bit = 1)
+      node = _nodeId = [
+        seedBytes[0] | 0x01,
+        seedBytes[1], seedBytes[2], seedBytes[3], seedBytes[4], seedBytes[5]
+      ];
+    }
+    if (clockseq == null) {
+      // Per 4.2.2, randomize (14 bit) clockseq
+      clockseq = _clockseq = (seedBytes[6] << 8 | seedBytes[7]) & 0x3fff;
+    }
+  }
+
+  // UUID timestamps are 100 nano-second units since the Gregorian epoch,
+  // (1582-10-15 00:00).  JSNumbers aren't precise enough for this, so
+  // time is handled internally as 'msecs' (integer milliseconds) and 'nsecs'
+  // (100-nanoseconds offset from msecs) since unix epoch, 1970-01-01 00:00.
+  var msecs = options.msecs !== undefined ? options.msecs : new Date().getTime();
+
+  // Per 4.2.1.2, use count of uuid's generated during the current clock
+  // cycle to simulate higher resolution clock
+  var nsecs = options.nsecs !== undefined ? options.nsecs : _lastNSecs + 1;
+
+  // Time since last uuid creation (in msecs)
+  var dt = (msecs - _lastMSecs) + (nsecs - _lastNSecs)/10000;
+
+  // Per 4.2.1.2, Bump clockseq on clock regression
+  if (dt < 0 && options.clockseq === undefined) {
+    clockseq = clockseq + 1 & 0x3fff;
+  }
+
+  // Reset nsecs if clock regresses (new clockseq) or we've moved onto a new
+  // time interval
+  if ((dt < 0 || msecs > _lastMSecs) && options.nsecs === undefined) {
+    nsecs = 0;
+  }
+
+  // Per 4.2.1.2 Throw error if too many uuids are requested
+  if (nsecs >= 10000) {
+    throw new Error('uuid.v1(): Can\'t create more than 10M uuids/sec');
+  }
+
+  _lastMSecs = msecs;
+  _lastNSecs = nsecs;
+  _clockseq = clockseq;
+
+  // Per 4.1.4 - Convert from unix epoch to Gregorian epoch
+  msecs += 12219292800000;
+
+  // `time_low`
+  var tl = ((msecs & 0xfffffff) * 10000 + nsecs) % 0x100000000;
+  b[i++] = tl >>> 24 & 0xff;
+  b[i++] = tl >>> 16 & 0xff;
+  b[i++] = tl >>> 8 & 0xff;
+  b[i++] = tl & 0xff;
+
+  // `time_mid`
+  var tmh = (msecs / 0x100000000 * 10000) & 0xfffffff;
+  b[i++] = tmh >>> 8 & 0xff;
+  b[i++] = tmh & 0xff;
+
+  // `time_high_and_version`
+  b[i++] = tmh >>> 24 & 0xf | 0x10; // include version
+  b[i++] = tmh >>> 16 & 0xff;
+
+  // `clock_seq_hi_and_reserved` (Per 4.2.2 - include variant)
+  b[i++] = clockseq >>> 8 | 0x80;
+
+  // `clock_seq_low`
+  b[i++] = clockseq & 0xff;
+
+  // `node`
+  for (var n = 0; n < 6; ++n) {
+    b[i + n] = node[n];
+  }
+
+  return buf ? buf : bytesToUuid(b);
+}
+
+module.exports = v1;
+
+},{"8":8,"9":9}],11:[function(_dereq_,module,exports){
+var rng = _dereq_(9);
+var bytesToUuid = _dereq_(8);
+
+function v4(options, buf, offset) {
+  var i = buf && offset || 0;
+
+  if (typeof(options) == 'string') {
+    buf = options === 'binary' ? new Array(16) : null;
+    options = null;
+  }
+  options = options || {};
+
+  var rnds = options.random || (options.rng || rng)();
+
+  // Per 4.4, set bits for version and `clock_seq_hi_and_reserved`
+  rnds[6] = (rnds[6] & 0x0f) | 0x40;
+  rnds[8] = (rnds[8] & 0x3f) | 0x80;
+
+  // Copy bytes to buffer, if provided
+  if (buf) {
+    for (var ii = 0; ii < 16; ++ii) {
+      buf[i + ii] = rnds[ii];
+    }
+  }
+
+  return buf || bytesToUuid(rnds);
+}
+
+module.exports = v4;
+
+},{"8":8,"9":9}],12:[function(_dereq_,module,exports){
+'use strict';
+
+/**
+ * Stringify/parse functions that don't operate
+ * recursively, so they avoid call stack exceeded
+ * errors.
+ */
+exports.stringify = function stringify(input) {
+  var queue = [];
+  queue.push({obj: input});
+
+  var res = '';
+  var next, obj, prefix, val, i, arrayPrefix, keys, k, key, value, objPrefix;
+  while ((next = queue.pop())) {
+    obj = next.obj;
+    prefix = next.prefix || '';
+    val = next.val || '';
+    res += prefix;
+    if (val) {
+      res += val;
+    } else if (typeof obj !== 'object') {
+      res += typeof obj === 'undefined' ? null : JSON.stringify(obj);
+    } else if (obj === null) {
+      res += 'null';
+    } else if (Array.isArray(obj)) {
+      queue.push({val: ']'});
+      for (i = obj.length - 1; i >= 0; i--) {
+        arrayPrefix = i === 0 ? '' : ',';
+        queue.push({obj: obj[i], prefix: arrayPrefix});
+      }
+      queue.push({val: '['});
+    } else { // object
+      keys = [];
+      for (k in obj) {
+        if (obj.hasOwnProperty(k)) {
+          keys.push(k);
+        }
+      }
+      queue.push({val: '}'});
+      for (i = keys.length - 1; i >= 0; i--) {
+        key = keys[i];
+        value = obj[key];
+        objPrefix = (i > 0 ? ',' : '');
+        objPrefix += JSON.stringify(key) + ':';
+        queue.push({obj: value, prefix: objPrefix});
+      }
+      queue.push({val: '{'});
+    }
+  }
+  return res;
+};
+
+// Convenience function for the parse function.
+// This pop function is basically copied from
+// pouchCollate.parseIndexableString
+function pop(obj, stack, metaStack) {
+  var lastMetaElement = metaStack[metaStack.length - 1];
+  if (obj === lastMetaElement.element) {
+    // popping a meta-element, e.g. an object whose value is another object
+    metaStack.pop();
+    lastMetaElement = metaStack[metaStack.length - 1];
+  }
+  var element = lastMetaElement.element;
+  var lastElementIndex = lastMetaElement.index;
+  if (Array.isArray(element)) {
+    element.push(obj);
+  } else if (lastElementIndex === stack.length - 2) { // obj with key+value
+    var key = stack.pop();
+    element[key] = obj;
+  } else {
+    stack.push(obj); // obj with key only
+  }
+}
+
+exports.parse = function (str) {
+  var stack = [];
+  var metaStack = []; // stack for arrays and objects
+  var i = 0;
+  var collationIndex,parsedNum,numChar;
+  var parsedString,lastCh,numConsecutiveSlashes,ch;
+  var arrayElement, objElement;
+  while (true) {
+    collationIndex = str[i++];
+    if (collationIndex === '}' ||
+        collationIndex === ']' ||
+        typeof collationIndex === 'undefined') {
+      if (stack.length === 1) {
+        return stack.pop();
+      } else {
+        pop(stack.pop(), stack, metaStack);
+        continue;
+      }
+    }
+    switch (collationIndex) {
+      case ' ':
+      case '\t':
+      case '\n':
+      case ':':
+      case ',':
+        break;
+      case 'n':
+        i += 3; // 'ull'
+        pop(null, stack, metaStack);
+        break;
+      case 't':
+        i += 3; // 'rue'
+        pop(true, stack, metaStack);
+        break;
+      case 'f':
+        i += 4; // 'alse'
+        pop(false, stack, metaStack);
+        break;
+      case '0':
+      case '1':
+      case '2':
+      case '3':
+      case '4':
+      case '5':
+      case '6':
+      case '7':
+      case '8':
+      case '9':
+      case '-':
+        parsedNum = '';
+        i--;
+        while (true) {
+          numChar = str[i++];
+          if (/[\d\.\-e\+]/.test(numChar)) {
+            parsedNum += numChar;
+          } else {
+            i--;
+            break;
+          }
+        }
+        pop(parseFloat(parsedNum), stack, metaStack);
+        break;
+      case '"':
+        parsedString = '';
+        lastCh = void 0;
+        numConsecutiveSlashes = 0;
+        while (true) {
+          ch = str[i++];
+          if (ch !== '"' || (lastCh === '\\' &&
+              numConsecutiveSlashes % 2 === 1)) {
+            parsedString += ch;
+            lastCh = ch;
+            if (lastCh === '\\') {
+              numConsecutiveSlashes++;
+            } else {
+              numConsecutiveSlashes = 0;
+            }
+          } else {
+            break;
+          }
+        }
+        pop(JSON.parse('"' + parsedString + '"'), stack, metaStack);
+        break;
+      case '[':
+        arrayElement = { element: [], index: stack.length };
+        stack.push(arrayElement.element);
+        metaStack.push(arrayElement);
+        break;
+      case '{':
+        objElement = { element: {}, index: stack.length };
+        stack.push(objElement.element);
+        metaStack.push(objElement);
+        break;
+      default:
+        throw new Error(
+          'unexpectedly reached end of input: ' + collationIndex);
+    }
+  }
+};
+
+},{}],13:[function(_dereq_,module,exports){
+(function (process,global){
+'use strict';
+
+function _interopDefault (ex) { return (ex && (typeof ex === 'object') && 'default' in ex) ? ex['default'] : ex; }
+
+var immediate = _interopDefault(_dereq_(3));
+var uuidV4 = _interopDefault(_dereq_(7));
+var Md5 = _interopDefault(_dereq_(6));
+var vuvuzela = _interopDefault(_dereq_(12));
+var getArguments = _interopDefault(_dereq_(1));
+var inherits = _interopDefault(_dereq_(4));
+var events = _dereq_(2);
+
+function mangle(key) {
+  return '$' + key;
+}
+function unmangle(key) {
+  return key.substring(1);
+}
+function Map$1() {
+  this._store = {};
+}
+Map$1.prototype.get = function (key) {
+  var mangled = mangle(key);
+  return this._store[mangled];
+};
+Map$1.prototype.set = function (key, value) {
+  var mangled = mangle(key);
+  this._store[mangled] = value;
+  return true;
+};
+Map$1.prototype.has = function (key) {
+  var mangled = mangle(key);
+  return mangled in this._store;
+};
+Map$1.prototype["delete"] = function (key) {
+  var mangled = mangle(key);
+  var res = mangled in this._store;
+  delete this._store[mangled];
+  return res;
+};
+Map$1.prototype.forEach = function (cb) {
+  var keys = Object.keys(this._store);
+  for (var i = 0, len = keys.length; i < len; i++) {
+    var key = keys[i];
+    var value = this._store[key];
+    key = unmangle(key);
+    cb(value, key);
+  }
+};
+Object.defineProperty(Map$1.prototype, 'size', {
+  get: function () {
+    return Object.keys(this._store).length;
+  }
+});
+
+function Set$1(array) {
+  this._store = new Map$1();
+
+  // init with an array
+  if (array && Array.isArray(array)) {
+    for (var i = 0, len = array.length; i < len; i++) {
+      this.add(array[i]);
+    }
+  }
+}
+Set$1.prototype.add = function (key) {
+  return this._store.set(key, true);
+};
+Set$1.prototype.has = function (key) {
+  return this._store.has(key);
+};
+Set$1.prototype.forEach = function (cb) {
+  this._store.forEach(function (value, key) {
+    cb(key);
+  });
+};
+Object.defineProperty(Set$1.prototype, 'size', {
+  get: function () {
+    return this._store.size;
+  }
+});
+
+/* global Map,Set,Symbol */
+// Based on https://kangax.github.io/compat-table/es6/ we can sniff out
+// incomplete Map/Set implementations which would otherwise cause our tests to fail.
+// Notably they fail in IE11 and iOS 8.4, which this prevents.
+function supportsMapAndSet() {
+  if (typeof Symbol === 'undefined' || typeof Map === 'undefined' || typeof Set === 'undefined') {
+    return false;
+  }
+  var prop = Object.getOwnPropertyDescriptor(Map, Symbol.species);
+  return prop && 'get' in prop && Map[Symbol.species] === Map;
+}
+
+// based on https://github.com/montagejs/collections
+
+var ExportedSet;
+var ExportedMap;
+
+{
+  if (supportsMapAndSet()) { // prefer built-in Map/Set
+    ExportedSet = Set;
+    ExportedMap = Map;
+  } else { // fall back to our polyfill
+    ExportedSet = Set$1;
+    ExportedMap = Map$1;
+  }
+}
+
+function isBinaryObject(object) {
+  return (typeof ArrayBuffer !== 'undefined' && object instanceof ArrayBuffer) ||
+    (typeof Blob !== 'undefined' && object instanceof Blob);
+}
+
+function cloneArrayBuffer(buff) {
+  if (typeof buff.slice === 'function') {
+    return buff.slice(0);
+  }
+  // IE10-11 slice() polyfill
+  var target = new ArrayBuffer(buff.byteLength);
+  var targetArray = new Uint8Array(target);
+  var sourceArray = new Uint8Array(buff);
+  targetArray.set(sourceArray);
+  return target;
+}
+
+function cloneBinaryObject(object) {
+  if (object instanceof ArrayBuffer) {
+    return cloneArrayBuffer(object);
+  }
+  var size = object.size;
+  var type = object.type;
+  // Blob
+  if (typeof object.slice === 'function') {
+    return object.slice(0, size, type);
+  }
+  // PhantomJS slice() replacement
+  return object.webkitSlice(0, size, type);
+}
+
+// most of this is borrowed from lodash.isPlainObject:
+// https://github.com/fis-components/lodash.isplainobject/
+// blob/29c358140a74f252aeb08c9eb28bef86f2217d4a/index.js
+
+var funcToString = Function.prototype.toString;
+var objectCtorString = funcToString.call(Object);
+
+function isPlainObject(value) {
+  var proto = Object.getPrototypeOf(value);
+  /* istanbul ignore if */
+  if (proto === null) { // not sure when this happens, but I guess it can
+    return true;
+  }
+  var Ctor = proto.constructor;
+  return (typeof Ctor == 'function' &&
+    Ctor instanceof Ctor && funcToString.call(Ctor) == objectCtorString);
+}
+
+function clone(object) {
+  var newObject;
+  var i;
+  var len;
+
+  if (!object || typeof object !== 'object') {
+    return object;
+  }
+
+  if (Array.isArray(object)) {
+    newObject = [];
+    for (i = 0, len = object.length; i < len; i++) {
+      newObject[i] = clone(object[i]);
+    }
+    return newObject;
+  }
+
+  // special case: to avoid inconsistencies between IndexedDB
+  // and other backends, we automatically stringify Dates
+  if (object instanceof Date) {
+    return object.toISOString();
+  }
+
+  if (isBinaryObject(object)) {
+    return cloneBinaryObject(object);
+  }
+
+  if (!isPlainObject(object)) {
+    return object; // don't clone objects like Workers
+  }
+
+  newObject = {};
+  for (i in object) {
+    /* istanbul ignore else */
+    if (Object.prototype.hasOwnProperty.call(object, i)) {
+      var value = clone(object[i]);
+      if (typeof value !== 'undefined') {
+        newObject[i] = value;
+      }
+    }
+  }
+  return newObject;
+}
+
+function once(fun) {
+  var called = false;
+  return getArguments(function (args) {
+    /* istanbul ignore if */
+    if (called) {
+      // this is a smoke test and should never actually happen
+      throw new Error('once called more than once');
+    } else {
+      called = true;
+      fun.apply(this, args);
+    }
+  });
+}
+
+function toPromise(func) {
+  //create the function we will be returning
+  return getArguments(function (args) {
+    // Clone arguments
+    args = clone(args);
+    var self = this;
+    // if the last argument is a function, assume its a callback
+    var usedCB = (typeof args[args.length - 1] === 'function') ? args.pop() : false;
+    var promise = new Promise(function (fulfill, reject) {
+      var resp;
+      try {
+        var callback = once(function (err, mesg) {
+          if (err) {
+            reject(err);
+          } else {
+            fulfill(mesg);
+          }
+        });
+        // create a callback for this invocation
+        // apply the function in the orig context
+        args.push(callback);
+        resp = func.apply(self, args);
+        if (resp && typeof resp.then === 'function') {
+          fulfill(resp);
+        }
+      } catch (e) {
+        reject(e);
+      }
+    });
+    // if there is a callback, call it back
+    if (usedCB) {
+      promise.then(function (result) {
+        usedCB(null, result);
+      }, usedCB);
+    }
+    return promise;
+  });
+}
+
+function logApiCall(self, name, args) {
+  /* istanbul ignore if */
+  if (self.constructor.listeners('debug').length) {
+    var logArgs = ['api', self.name, name];
+    for (var i = 0; i < args.length - 1; i++) {
+      logArgs.push(args[i]);
+    }
+    self.constructor.emit('debug', logArgs);
+
+    // override the callback itself to log the response
+    var origCallback = args[args.length - 1];
+    args[args.length - 1] = function (err, res) {
+      var responseArgs = ['api', self.name, name];
+      responseArgs = responseArgs.concat(
+        err ? ['error', err] : ['success', res]
+      );
+      self.constructor.emit('debug', responseArgs);
+      origCallback(err, res);
+    };
+  }
+}
+
+function adapterFun(name, callback) {
+  return toPromise(getArguments(function (args) {
+    if (this._closed) {
+      return Promise.reject(new Error('database is closed'));
+    }
+    if (this._destroyed) {
+      return Promise.reject(new Error('database is destroyed'));
+    }
+    var self = this;
+    logApiCall(self, name, args);
+    if (!this.taskqueue.isReady) {
+      return new Promise(function (fulfill, reject) {
+        self.taskqueue.addTask(function (failed) {
+          if (failed) {
+            reject(failed);
+          } else {
+            fulfill(self[name].apply(self, args));
+          }
+        });
+      });
+    }
+    return callback.apply(this, args);
+  }));
+}
+
+// like underscore/lodash _.pick()
+function pick(obj, arr) {
+  var res = {};
+  for (var i = 0, len = arr.length; i < len; i++) {
+    var prop = arr[i];
+    if (prop in obj) {
+      res[prop] = obj[prop];
+    }
+  }
+  return res;
+}
+
+// Most browsers throttle concurrent requests at 6, so it's silly
+// to shim _bulk_get by trying to launch potentially hundreds of requests
+// and then letting the majority time out. We can handle this ourselves.
+var MAX_NUM_CONCURRENT_REQUESTS = 6;
+
+function identityFunction(x) {
+  return x;
+}
+
+function formatResultForOpenRevsGet(result) {
+  return [{
+    ok: result
+  }];
+}
+
+// shim for P/CouchDB adapters that don't directly implement _bulk_get
+function bulkGet(db, opts, callback) {
+  var requests = opts.docs;
+
+  // consolidate into one request per doc if possible
+  var requestsById = new ExportedMap();
+  requests.forEach(function (request) {
+    if (requestsById.has(request.id)) {
+      requestsById.get(request.id).push(request);
+    } else {
+      requestsById.set(request.id, [request]);
+    }
+  });
+
+  var numDocs = requestsById.size;
+  var numDone = 0;
+  var perDocResults = new Array(numDocs);
+
+  function collapseResultsAndFinish() {
+    var results = [];
+    perDocResults.forEach(function (res) {
+      res.docs.forEach(function (info) {
+        results.push({
+          id: res.id,
+          docs: [info]
+        });
+      });
+    });
+    callback(null, {results: results});
+  }
+
+  function checkDone() {
+    if (++numDone === numDocs) {
+      collapseResultsAndFinish();
+    }
+  }
+
+  function gotResult(docIndex, id, docs) {
+    perDocResults[docIndex] = {id: id, docs: docs};
+    checkDone();
+  }
+
+  var allRequests = [];
+  requestsById.forEach(function (value, key) {
+    allRequests.push(key);
+  });
+
+  var i = 0;
+
+  function nextBatch() {
+
+    if (i >= allRequests.length) {
+      return;
+    }
+
+    var upTo = Math.min(i + MAX_NUM_CONCURRENT_REQUESTS, allRequests.length);
+    var batch = allRequests.slice(i, upTo);
+    processBatch(batch, i);
+    i += batch.length;
+  }
+
+  function processBatch(batch, offset) {
+    batch.forEach(function (docId, j) {
+      var docIdx = offset + j;
+      var docRequests = requestsById.get(docId);
+
+      // just use the first request as the "template"
+      // TODO: The _bulk_get API allows for more subtle use cases than this,
+      // but for now it is unlikely that there will be a mix of different
+      // "atts_since" or "attachments" in the same request, since it's just
+      // replicate.js that is using this for the moment.
+      // Also, atts_since is aspirational, since we don't support it yet.
+      var docOpts = pick(docRequests[0], ['atts_since', 'attachments']);
+      docOpts.open_revs = docRequests.map(function (request) {
+        // rev is optional, open_revs disallowed
+        return request.rev;
+      });
+
+      // remove falsey / undefined revisions
+      docOpts.open_revs = docOpts.open_revs.filter(identityFunction);
+
+      var formatResult = identityFunction;
+
+      if (docOpts.open_revs.length === 0) {
+        delete docOpts.open_revs;
+
+        // when fetching only the "winning" leaf,
+        // transform the result so it looks like an open_revs
+        // request
+        formatResult = formatResultForOpenRevsGet;
+      }
+
+      // globally-supplied options
+      ['revs', 'attachments', 'binary', 'ajax', 'latest'].forEach(function (param) {
+        if (param in opts) {
+          docOpts[param] = opts[param];
+        }
+      });
+      db.get(docId, docOpts, function (err, res) {
+        var result;
+        /* istanbul ignore if */
+        if (err) {
+          result = [{error: err}];
+        } else {
+          result = formatResult(res);
+        }
+        gotResult(docIdx, docId, result);
+        nextBatch();
+      });
+    });
+  }
+
+  nextBatch();
+
+}
+
+var hasLocal;
+
+try {
+  localStorage.setItem('_pouch_check_localstorage', 1);
+  hasLocal = !!localStorage.getItem('_pouch_check_localstorage');
+} catch (e) {
+  hasLocal = false;
+}
+
+function hasLocalStorage() {
+  return hasLocal;
+}
+
+// Custom nextTick() shim for browsers. In node, this will just be process.nextTick(). We
+
+inherits(Changes, events.EventEmitter);
+
+/* istanbul ignore next */
+function attachBrowserEvents(self) {
+  if (hasLocalStorage()) {
+    addEventListener("storage", function (e) {
+      self.emit(e.key);
+    });
+  }
+}
+
+function Changes() {
+  events.EventEmitter.call(this);
+  this._listeners = {};
+
+  attachBrowserEvents(this);
+}
+Changes.prototype.addListener = function (dbName, id, db, opts) {
+  /* istanbul ignore if */
+  if (this._listeners[id]) {
+    return;
+  }
+  var self = this;
+  var inprogress = false;
+  function eventFunction() {
+    /* istanbul ignore if */
+    if (!self._listeners[id]) {
+      return;
+    }
+    if (inprogress) {
+      inprogress = 'waiting';
+      return;
+    }
+    inprogress = true;
+    var changesOpts = pick(opts, [
+      'style', 'include_docs', 'attachments', 'conflicts', 'filter',
+      'doc_ids', 'view', 'since', 'query_params', 'binary', 'return_docs'
+    ]);
+
+    /* istanbul ignore next */
+    function onError() {
+      inprogress = false;
+    }
+
+    db.changes(changesOpts).on('change', function (c) {
+      if (c.seq > opts.since && !opts.cancelled) {
+        opts.since = c.seq;
+        opts.onChange(c);
+      }
+    }).on('complete', function () {
+      if (inprogress === 'waiting') {
+        immediate(eventFunction);
+      }
+      inprogress = false;
+    }).on('error', onError);
+  }
+  this._listeners[id] = eventFunction;
+  this.on(dbName, eventFunction);
+};
+
+Changes.prototype.removeListener = function (dbName, id) {
+  /* istanbul ignore if */
+  if (!(id in this._listeners)) {
+    return;
+  }
+  events.EventEmitter.prototype.removeListener.call(this, dbName,
+    this._listeners[id]);
+  delete this._listeners[id];
+};
+
+
+/* istanbul ignore next */
+Changes.prototype.notifyLocalWindows = function (dbName) {
+  //do a useless change on a storage thing
+  //in order to get other windows's listeners to activate
+  if (hasLocalStorage()) {
+    localStorage[dbName] = (localStorage[dbName] === "a") ? "b" : "a";
+  }
+};
+
+Changes.prototype.notify = function (dbName) {
+  this.emit(dbName);
+  this.notifyLocalWindows(dbName);
+};
+
+function guardedConsole(method) {
+  /* istanbul ignore else */
+  if (typeof console !== 'undefined' && typeof console[method] === 'function') {
+    var args = Array.prototype.slice.call(arguments, 1);
+    console[method].apply(console, args);
+  }
+}
+
+function randomNumber(min, max) {
+  var maxTimeout = 600000; // Hard-coded default of 10 minutes
+  min = parseInt(min, 10) || 0;
+  max = parseInt(max, 10);
+  if (max !== max || max <= min) {
+    max = (min || 1) << 1; //doubling
+  } else {
+    max = max + 1;
+  }
+  // In order to not exceed maxTimeout, pick a random value between half of maxTimeout and maxTimeout
+  if (max > maxTimeout) {
+    min = maxTimeout >> 1; // divide by two
+    max = maxTimeout;
+  }
+  var ratio = Math.random();
+  var range = max - min;
+
+  return ~~(range * ratio + min); // ~~ coerces to an int, but fast.
+}
+
+function defaultBackOff(min) {
+  var max = 0;
+  if (!min) {
+    max = 2000;
+  }
+  return randomNumber(min, max);
+}
+
+// designed to give info to browser users, who are disturbed
+// when they see http errors in the console
+function explainError(status, str) {
+  guardedConsole('info', 'The above ' + status + ' is totally normal. ' + str);
+}
+
+var assign;
+{
+  if (typeof Object.assign === 'function') {
+    assign = Object.assign;
+  } else {
+    // lite Object.assign polyfill based on
+    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
+    assign = function (target) {
+      var to = Object(target);
+
+      for (var index = 1; index < arguments.length; index++) {
+        var nextSource = arguments[index];
+
+        if (nextSource != null) { // Skip over if undefined or null
+          for (var nextKey in nextSource) {
+            // Avoid bugs when hasOwnProperty is shadowed
+            if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
+              to[nextKey] = nextSource[nextKey];
+            }
+          }
+        }
+      }
+      return to;
+    };
+  }
+}
+
+var $inject_Object_assign = assign;
+
+inherits(PouchError, Error);
+
+function PouchError(status, error, reason) {
+  Error.call(this, reason);
+  this.status = status;
+  this.name = error;
+  this.message = reason;
+  this.error = true;
+}
+
+PouchError.prototype.toString = function () {
+  return JSON.stringify({
+    status: this.status,
+    name: this.name,
+    message: this.message,
+    reason: this.reason
+  });
+};
+
+var UNAUTHORIZED = new PouchError(401, 'unauthorized', "Name or password is incorrect.");
+var MISSING_BULK_DOCS = new PouchError(400, 'bad_request', "Missing JSON list of 'docs'");
+var MISSING_DOC = new PouchError(404, 'not_found', 'missing');
+var REV_CONFLICT = new PouchError(409, 'conflict', 'Document update conflict');
+var INVALID_ID = new PouchError(400, 'bad_request', '_id field must contain a string');
+var MISSING_ID = new PouchError(412, 'missing_id', '_id is required for puts');
+var RESERVED_ID = new PouchError(400, 'bad_request', 'Only reserved document ids may start with underscore.');
+var NOT_OPEN = new PouchError(412, 'precondition_failed', 'Database not open');
+var UNKNOWN_ERROR = new PouchError(500, 'unknown_error', 'Database encountered an unknown error');
+var BAD_ARG = new PouchError(500, 'badarg', 'Some query argument is invalid');
+var INVALID_REQUEST = new PouchError(400, 'invalid_request', 'Request was invalid');
+var QUERY_PARSE_ERROR = new PouchError(400, 'query_parse_error', 'Some query parameter is invalid');
+var DOC_VALIDATION = new PouchError(500, 'doc_validation', 'Bad special document member');
+var BAD_REQUEST = new PouchError(400, 'bad_request', 'Something wrong with the request');
+var NOT_AN_OBJECT = new PouchError(400, 'bad_request', 'Document must be a JSON object');
+var DB_MISSING = new PouchError(404, 'not_found', 'Database not found');
+var IDB_ERROR = new PouchError(500, 'indexed_db_went_bad', 'unknown');
+var WSQ_ERROR = new PouchError(500, 'web_sql_went_bad', 'unknown');
+var LDB_ERROR = new PouchError(500, 'levelDB_went_went_bad', 'unknown');
+var FORBIDDEN = new PouchError(403, 'forbidden', 'Forbidden by design doc validate_doc_update function');
+var INVALID_REV = new PouchError(400, 'bad_request', 'Invalid rev format');
+var FILE_EXISTS = new PouchError(412, 'file_exists', 'The database could not be created, the file already exists.');
+var MISSING_STUB = new PouchError(412, 'missing_stub', 'A pre-existing attachment stub wasn\'t found');
+var INVALID_URL = new PouchError(413, 'invalid_url', 'Provided URL is invalid');
+
+function createError(error, reason) {
+  function CustomPouchError(reason) {
+    // inherit error properties from our parent error manually
+    // so as to allow proper JSON parsing.
+    /* jshint ignore:start */
+    for (var p in error) {
+      if (typeof error[p] !== 'function') {
+        this[p] = error[p];
+      }
+    }
+    /* jshint ignore:end */
+    if (reason !== undefined) {
+      this.reason = reason;
+    }
+  }
+  CustomPouchError.prototype = PouchError.prototype;
+  return new CustomPouchError(reason);
+}
+
+function generateErrorFromResponse(err) {
+
+  if (typeof err !== 'object') {
+    var data = err;
+    err = UNKNOWN_ERROR;
+    err.data = data;
+  }
+
+  if ('error' in err && err.error === 'conflict') {
+    err.name = 'conflict';
+    err.status = 409;
+  }
+
+  if (!('name' in err)) {
+    err.name = err.error || 'unknown';
+  }
+
+  if (!('status' in err)) {
+    err.status = 500;
+  }
+
+  if (!('message' in err)) {
+    err.message = err.message || err.reason;
+  }
+
+  return err;
+}
+
+function tryFilter(filter, doc, req) {
+  try {
+    return !filter(doc, req);
+  } catch (err) {
+    var msg = 'Filter function threw: ' + err.toString();
+    return createError(BAD_REQUEST, msg);
+  }
+}
+
+function filterChange(opts) {
+  var req = {};
+  var hasFilter = opts.filter && typeof opts.filter === 'function';
+  req.query = opts.query_params;
+
+  return function filter(change) {
+    if (!change.doc) {
+      // CSG sends events on the changes feed that don't have documents,
+      // this hack makes a whole lot of existing code robust.
+      change.doc = {};
+    }
+
+    var filterReturn = hasFilter && tryFilter(opts.filter, change.doc, req);
+
+    if (typeof filterReturn === 'object') {
+      return filterReturn;
+    }
+
+    if (filterReturn) {
+      return false;
+    }
+
+    if (!opts.include_docs) {
+      delete change.doc;
+    } else if (!opts.attachments) {
+      for (var att in change.doc._attachments) {
+        /* istanbul ignore else */
+        if (change.doc._attachments.hasOwnProperty(att)) {
+          change.doc._attachments[att].stub = true;
+        }
+      }
+    }
+    return true;
+  };
+}
+
+function flatten(arrs) {
+  var res = [];
+  for (var i = 0, len = arrs.length; i < len; i++) {
+    res = res.concat(arrs[i]);
+  }
+  return res;
+}
+
+// shim for Function.prototype.name,
+
+// Determine id an ID is valid
+//   - invalid IDs begin with an underescore that does not begin '_design' or
+//     '_local'
+//   - any other string value is a valid id
+// Returns the specific error object for each case
+function invalidIdError(id) {
+  var err;
+  if (!id) {
+    err = createError(MISSING_ID);
+  } else if (typeof id !== 'string') {
+    err = createError(INVALID_ID);
+  } else if (/^_/.test(id) && !(/^_(design|local)/).test(id)) {
+    err = createError(RESERVED_ID);
+  }
+  if (err) {
+    throw err;
+  }
+}
+
+// Checks if a PouchDB object is "remote" or not. This is
+
+function isRemote(db) {
+  if (typeof db._remote === 'boolean') {
+    return db._remote;
+  }
+  /* istanbul ignore next */
+  if (typeof db.type === 'function') {
+    guardedConsole('warn',
+      'db.type() is deprecated and will be removed in ' +
+      'a future version of PouchDB');
+    return db.type() === 'http';
+  }
+  /* istanbul ignore next */
+  return false;
+}
+
+function listenerCount(ee, type) {
+  return 'listenerCount' in ee ? ee.listenerCount(type) :
+                                 events.EventEmitter.listenerCount(ee, type);
+}
+
+function parseDesignDocFunctionName(s) {
+  if (!s) {
+    return null;
+  }
+  var parts = s.split('/');
+  if (parts.length === 2) {
+    return parts;
+  }
+  if (parts.length === 1) {
+    return [s, s];
+  }
+  return null;
+}
+
+function normalizeDesignDocFunctionName(s) {
+  var normalized = parseDesignDocFunctionName(s);
+  return normalized ? normalized.join('/') : null;
+}
+
+// originally parseUri 1.2.2, now patched by us
+// (c) Steven Levithan <stevenlevithan.com>
+// MIT License
+var keys = ["source", "protocol", "authority", "userInfo", "user", "password",
+    "host", "port", "relative", "path", "directory", "file", "query", "anchor"];
+var qName ="queryKey";
+var qParser = /(?:^|&)([^&=]*)=?([^&]*)/g;
+
+// use the "loose" parser
+/* eslint maxlen: 0, no-useless-escape: 0 */
+var parser = /^(?:(?![^:@]+:[^:@\/]*@)([^:\/?#.]+):)?(?:\/\/)?((?:(([^:@]*)(?::([^:@]*))?)?@)?([^:\/?#]*)(?::(\d*))?)(((\/(?:[^?#](?![^?#\/]*\.[^?#\/.]+(?:[?#]|$)))*\/?)?([^?#\/]*))(?:\?([^#]*))?(?:#(.*))?)/;
+
+function parseUri(str) {
+  var m = parser.exec(str);
+  var uri = {};
+  var i = 14;
+
+  while (i--) {
+    var key = keys[i];
+    var value = m[i] || "";
+    var encoded = ['user', 'password'].indexOf(key) !== -1;
+    uri[key] = encoded ? decodeURIComponent(value) : value;
+  }
+
+  uri[qName] = {};
+  uri[keys[12]].replace(qParser, function ($0, $1, $2) {
+    if ($1) {
+      uri[qName][$1] = $2;
+    }
+  });
+
+  return uri;
+}
+
+// Based on https://github.com/alexdavid/scope-eval v0.0.3
+// (source: https://unpkg.com/scope-eval@0.0.3/scope_eval.js)
+// This is basically just a wrapper around new Function()
+
+function scopeEval(source, scope) {
+  var keys = [];
+  var values = [];
+  for (var key in scope) {
+    if (scope.hasOwnProperty(key)) {
+      keys.push(key);
+      values.push(scope[key]);
+    }
+  }
+  keys.push(source);
+  return Function.apply(null, keys).apply(null, values);
+}
+
+// this is essentially the "update sugar" function from daleharvey/pouchdb#1388
+// the diffFun tells us what delta to apply to the doc.  it either returns
+// the doc, or false if it doesn't need to do an update after all
+function upsert(db, docId, diffFun) {
+  return new Promise(function (fulfill, reject) {
+    db.get(docId, function (err, doc) {
+      if (err) {
+        /* istanbul ignore next */
+        if (err.status !== 404) {
+          return reject(err);
+        }
+        doc = {};
+      }
+
+      // the user might change the _rev, so save it for posterity
+      var docRev = doc._rev;
+      var newDoc = diffFun(doc);
+
+      if (!newDoc) {
+        // if the diffFun returns falsy, we short-circuit as
+        // an optimization
+        return fulfill({updated: false, rev: docRev});
+      }
+
+      // users aren't allowed to modify these values,
+      // so reset them here
+      newDoc._id = docId;
+      newDoc._rev = docRev;
+      fulfill(tryAndPut(db, newDoc, diffFun));
+    });
+  });
+}
+
+function tryAndPut(db, doc, diffFun) {
+  return db.put(doc).then(function (res) {
+    return {
+      updated: true,
+      rev: res.rev
+    };
+  }, function (err) {
+    /* istanbul ignore next */
+    if (err.status !== 409) {
+      throw err;
+    }
+    return upsert(db, doc._id, diffFun);
+  });
+}
+
+var thisAtob = function (str) {
+  return atob(str);
+};
+
+var thisBtoa = function (str) {
+  return btoa(str);
+};
+
+// Abstracts constructing a Blob object, so it also works in older
+// browsers that don't support the native Blob constructor (e.g.
+// old QtWebKit versions, Android < 4.4).
+function createBlob(parts, properties) {
+  /* global BlobBuilder,MSBlobBuilder,MozBlobBuilder,WebKitBlobBuilder */
+  parts = parts || [];
+  properties = properties || {};
+  try {
+    return new Blob(parts, properties);
+  } catch (e) {
+    if (e.name !== "TypeError") {
+      throw e;
+    }
+    var Builder = typeof BlobBuilder !== 'undefined' ? BlobBuilder :
+                  typeof MSBlobBuilder !== 'undefined' ? MSBlobBuilder :
+                  typeof MozBlobBuilder !== 'undefined' ? MozBlobBuilder :
+                  WebKitBlobBuilder;
+    var builder = new Builder();
+    for (var i = 0; i < parts.length; i += 1) {
+      builder.append(parts[i]);
+    }
+    return builder.getBlob(properties.type);
+  }
+}
+
+// From http://stackoverflow.com/questions/14967647/ (continues on next line)
+// encode-decode-image-with-base64-breaks-image (2013-04-21)
+function binaryStringToArrayBuffer(bin) {
+  var length = bin.length;
+  var buf = new ArrayBuffer(length);
+  var arr = new Uint8Array(buf);
+  for (var i = 0; i < length; i++) {
+    arr[i] = bin.charCodeAt(i);
+  }
+  return buf;
+}
+
+function binStringToBluffer(binString, type) {
+  return createBlob([binaryStringToArrayBuffer(binString)], {type: type});
+}
+
+function b64ToBluffer(b64, type) {
+  return binStringToBluffer(thisAtob(b64), type);
+}
+
+//Can't find original post, but this is close
+//http://stackoverflow.com/questions/6965107/ (continues on next line)
+//converting-between-strings-and-arraybuffers
+function arrayBufferToBinaryString(buffer) {
+  var binary = '';
+  var bytes = new Uint8Array(buffer);
+  var length = bytes.byteLength;
+  for (var i = 0; i < length; i++) {
+    binary += String.fromCharCode(bytes[i]);
+  }
+  return binary;
+}
+
+// shim for browsers that don't support it
+function readAsBinaryString(blob, callback) {
+  var reader = new FileReader();
+  var hasBinaryString = typeof reader.readAsBinaryString === 'function';
+  reader.onloadend = function (e) {
+    var result = e.target.result || '';
+    if (hasBinaryString) {
+      return callback(result);
+    }
+    callback(arrayBufferToBinaryString(result));
+  };
+  if (hasBinaryString) {
+    reader.readAsBinaryString(blob);
+  } else {
+    reader.readAsArrayBuffer(blob);
+  }
+}
+
+function blobToBinaryString(blobOrBuffer, callback) {
+  readAsBinaryString(blobOrBuffer, function (bin) {
+    callback(bin);
+  });
+}
+
+function blobToBase64(blobOrBuffer, callback) {
+  blobToBinaryString(blobOrBuffer, function (base64) {
+    callback(thisBtoa(base64));
+  });
+}
+
+// simplified API. universal browser support is assumed
+function readAsArrayBuffer(blob, callback) {
+  var reader = new FileReader();
+  reader.onloadend = function (e) {
+    var result = e.target.result || new ArrayBuffer(0);
+    callback(result);
+  };
+  reader.readAsArrayBuffer(blob);
+}
+
+// this is not used in the browser
+
+var setImmediateShim = global.setImmediate || global.setTimeout;
+var MD5_CHUNK_SIZE = 32768;
+
+function rawToBase64(raw) {
+  return thisBtoa(raw);
+}
+
+function sliceBlob(blob, start, end) {
+  if (blob.webkitSlice) {
+    return blob.webkitSlice(start, end);
+  }
+  return blob.slice(start, end);
+}
+
+function appendBlob(buffer, blob, start, end, callback) {
+  if (start > 0 || end < blob.size) {
+    // only slice blob if we really need to
+    blob = sliceBlob(blob, start, end);
+  }
+  readAsArrayBuffer(blob, function (arrayBuffer) {
+    buffer.append(arrayBuffer);
+    callback();
+  });
+}
+
+function appendString(buffer, string, start, end, callback) {
+  if (start > 0 || end < string.length) {
+    // only create a substring if we really need to
+    string = string.substring(start, end);
+  }
+  buffer.appendBinary(string);
+  callback();
+}
+
+function binaryMd5(data, callback) {
+  var inputIsString = typeof data === 'string';
+  var len = inputIsString ? data.length : data.size;
+  var chunkSize = Math.min(MD5_CHUNK_SIZE, len);
+  var chunks = Math.ceil(len / chunkSize);
+  var currentChunk = 0;
+  var buffer = inputIsString ? new Md5() : new Md5.ArrayBuffer();
+
+  var append = inputIsString ? appendString : appendBlob;
+
+  function next() {
+    setImmediateShim(loadNextChunk);
+  }
+
+  function done() {
+    var raw = buffer.end(true);
+    var base64 = rawToBase64(raw);
+    callback(base64);
+    buffer.destroy();
+  }
+
+  function loadNextChunk() {
+    var start = currentChunk * chunkSize;
+    var end = start + chunkSize;
+    currentChunk++;
+    if (currentChunk < chunks) {
+      append(buffer, data, start, end, next);
+    } else {
+      append(buffer, data, start, end, done);
+    }
+  }
+  loadNextChunk();
+}
+
+function stringMd5(string) {
+  return Md5.hash(string);
+}
+
+function rev(doc, deterministic_revs) {
+  var clonedDoc = clone(doc);
+  if (!deterministic_revs) {
+    return uuidV4.v4().replace(/-/g, '').toLowerCase();
+  }
+
+  delete clonedDoc._rev_tree;
+  return stringMd5(JSON.stringify(clonedDoc));
+}
+
+var uuid = uuidV4.v4;
+
+// We fetch all leafs of the revision tree, and sort them based on tree length
+// and whether they were deleted, undeleted documents with the longest revision
+// tree (most edits) win
+// The final sort algorithm is slightly documented in a sidebar here:
+// http://guide.couchdb.org/draft/conflicts.html
+function winningRev(metadata) {
+  var winningId;
+  var winningPos;
+  var winningDeleted;
+  var toVisit = metadata.rev_tree.slice();
+  var node;
+  while ((node = toVisit.pop())) {
+    var tree = node.ids;
+    var branches = tree[2];
+    var pos = node.pos;
+    if (branches.length) { // non-leaf
+      for (var i = 0, len = branches.length; i < len; i++) {
+        toVisit.push({pos: pos + 1, ids: branches[i]});
+      }
+      continue;
+    }
+    var deleted = !!tree[1].deleted;
+    var id = tree[0];
+    // sort by deleted, then pos, then id
+    if (!winningId || (winningDeleted !== deleted ? winningDeleted :
+        winningPos !== pos ? winningPos < pos : winningId < id)) {
+      winningId = id;
+      winningPos = pos;
+      winningDeleted = deleted;
+    }
+  }
+
+  return winningPos + '-' + winningId;
+}
+
+// Pretty much all below can be combined into a higher order function to
+// traverse revisions
+// The return value from the callback will be passed as context to all
+// children of that node
+function traverseRevTree(revs, callback) {
+  var toVisit = revs.slice();
+
+  var node;
+  while ((node = toVisit.pop())) {
+    var pos = node.pos;
+    var tree = node.ids;
+    var branches = tree[2];
+    var newCtx =
+      callback(branches.length === 0, pos, tree[0], node.ctx, tree[1]);
+    for (var i = 0, len = branches.length; i < len; i++) {
+      toVisit.push({pos: pos + 1, ids: branches[i], ctx: newCtx});
+    }
+  }
+}
+
+function sortByPos(a, b) {
+  return a.pos - b.pos;
+}
+
+function collectLeaves(revs) {
+  var leaves = [];
+  traverseRevTree(revs, function (isLeaf, pos, id, acc, opts) {
+    if (isLeaf) {
+      leaves.push({rev: pos + "-" + id, pos: pos, opts: opts});
+    }
+  });
+  leaves.sort(sortByPos).reverse();
+  for (var i = 0, len = leaves.length; i < len; i++) {
+    delete leaves[i].pos;
+  }
+  return leaves;
+}
+
+// returns revs of all conflicts that is leaves such that
+// 1. are not deleted and
+// 2. are different than winning revision
+function collectConflicts(metadata) {
+  var win = winningRev(metadata);
+  var leaves = collectLeaves(metadata.rev_tree);
+  var conflicts = [];
+  for (var i = 0, len = leaves.length; i < len; i++) {
+    var leaf = leaves[i];
+    if (leaf.rev !== win && !leaf.opts.deleted) {
+      conflicts.push(leaf.rev);
+    }
+  }
+  return conflicts;
+}
+
+// compact a tree by marking its non-leafs as missing,
+// and return a list of revs to delete
+function compactTree(metadata) {
+  var revs = [];
+  traverseRevTree(metadata.rev_tree, function (isLeaf, pos,
+                                               revHash, ctx, opts) {
+    if (opts.status === 'available' && !isLeaf) {
+      revs.push(pos + '-' + revHash);
+      opts.status = 'missing';
+    }
+  });
+  return revs;
+}
+
+// build up a list of all the paths to the leafs in this revision tree
+function rootToLeaf(revs) {
+  var paths = [];
+  var toVisit = revs.slice();
+  var node;
+  while ((node = toVisit.pop())) {
+    var pos = node.pos;
+    var tree = node.ids;
+    var id = tree[0];
+    var opts = tree[1];
+    var branches = tree[2];
+    var isLeaf = branches.length === 0;
+
+    var history = node.history ? node.history.slice() : [];
+    history.push({id: id, opts: opts});
+    if (isLeaf) {
+      paths.push({pos: (pos + 1 - history.length), ids: history});
+    }
+    for (var i = 0, len = branches.length; i < len; i++) {
+      toVisit.push({pos: pos + 1, ids: branches[i], history: history});
+    }
+  }
+  return paths.reverse();
+}
+
+// for a better overview of what this is doing, read:
+
+function sortByPos$1(a, b) {
+  return a.pos - b.pos;
+}
+
+// classic binary search
+function binarySearch(arr, item, comparator) {
+  var low = 0;
+  var high = arr.length;
+  var mid;
+  while (low < high) {
+    mid = (low + high) >>> 1;
+    if (comparator(arr[mid], item) < 0) {
+      low = mid + 1;
+    } else {
+      high = mid;
+    }
+  }
+  return low;
+}
+
+// assuming the arr is sorted, insert the item in the proper place
+function insertSorted(arr, item, comparator) {
+  var idx = binarySearch(arr, item, comparator);
+  arr.splice(idx, 0, item);
+}
+
+// Turn a path as a flat array into a tree with a single branch.
+// If any should be stemmed from the beginning of the array, that's passed
+// in as the second argument
+function pathToTree(path, numStemmed) {
+  var root;
+  var leaf;
+  for (var i = numStemmed, len = path.length; i < len; i++) {
+    var node = path[i];
+    var currentLeaf = [node.id, node.opts, []];
+    if (leaf) {
+      leaf[2].push(currentLeaf);
+      leaf = currentLeaf;
+    } else {
+      root = leaf = currentLeaf;
+    }
+  }
+  return root;
+}
+
+// compare the IDs of two trees
+function compareTree(a, b) {
+  return a[0] < b[0] ? -1 : 1;
+}
+
+// Merge two trees together
+// The roots of tree1 and tree2 must be the same revision
+function mergeTree(in_tree1, in_tree2) {
+  var queue = [{tree1: in_tree1, tree2: in_tree2}];
+  var conflicts = false;
+  while (queue.length > 0) {
+    var item = queue.pop();
+    var tree1 = item.tree1;
+    var tree2 = item.tree2;
+
+    if (tree1[1].status || tree2[1].status) {
+      tree1[1].status =
+        (tree1[1].status ===  'available' ||
+        tree2[1].status === 'available') ? 'available' : 'missing';
+    }
+
+    for (var i = 0; i < tree2[2].length; i++) {
+      if (!tree1[2][0]) {
+        conflicts = 'new_leaf';
+        tree1[2][0] = tree2[2][i];
+        continue;
+      }
+
+      var merged = false;
+      for (var j = 0; j < tree1[2].length; j++) {
+        if (tree1[2][j][0] === tree2[2][i][0]) {
+          queue.push({tree1: tree1[2][j], tree2: tree2[2][i]});
+          merged = true;
+        }
+      }
+      if (!merged) {
+        conflicts = 'new_branch';
+        insertSorted(tree1[2], tree2[2][i], compareTree);
+      }
+    }
+  }
+  return {conflicts: conflicts, tree: in_tree1};
+}
+
+function doMerge(tree, path, dontExpand) {
+  var restree = [];
+  var conflicts = false;
+  var merged = false;
+  var res;
+
+  if (!tree.length) {
+    return {tree: [path], conflicts: 'new_leaf'};
+  }
+
+  for (var i = 0, len = tree.length; i < len; i++) {
+    var branch = tree[i];
+    if (branch.pos === path.pos && branch.ids[0] === path.ids[0]) {
+      // Paths start at the same position and have the same root, so they need
+      // merged
+      res = mergeTree(branch.ids, path.ids);
+      restree.push({pos: branch.pos, ids: res.tree});
+      conflicts = conflicts || res.conflicts;
+      merged = true;
+    } else if (dontExpand !== true) {
+      // The paths start at a different position, take the earliest path and
+      // traverse up until it as at the same point from root as the path we
+      // want to merge.  If the keys match we return the longer path with the
+      // other merged After stemming we dont want to expand the trees
+
+      var t1 = branch.pos < path.pos ? branch : path;
+      var t2 = branch.pos < path.pos ? path : branch;
+      var diff = t2.pos - t1.pos;
+
+      var candidateParents = [];
+
+      var trees = [];
+      trees.push({ids: t1.ids, diff: diff, parent: null, parentIdx: null});
+      while (trees.length > 0) {
+        var item = trees.pop();
+        if (item.diff === 0) {
+          if (item.ids[0] === t2.ids[0]) {
+            candidateParents.push(item);
+          }
+          continue;
+        }
+        var elements = item.ids[2];
+        for (var j = 0, elementsLen = elements.length; j < elementsLen; j++) {
+          trees.push({
+            ids: elements[j],
+            diff: item.diff - 1,
+            parent: item.ids,
+            parentIdx: j
+          });
+        }
+      }
+
+      var el = candidateParents[0];
+
+      if (!el) {
+        restree.push(branch);
+      } else {
+        res = mergeTree(el.ids, t2.ids);
+        el.parent[2][el.parentIdx] = res.tree;
+        restree.push({pos: t1.pos, ids: t1.ids});
+        conflicts = conflicts || res.conflicts;
+        merged = true;
+      }
+    } else {
+      restree.push(branch);
+    }
+  }
+
+  // We didnt find
+  if (!merged) {
+    restree.push(path);
+  }
+
+  restree.sort(sortByPos$1);
+
+  return {
+    tree: restree,
+    conflicts: conflicts || 'internal_node'
+  };
+}
+
+// To ensure we dont grow the revision tree infinitely, we stem old revisions
+function stem(tree, depth) {
+  // First we break out the tree into a complete list of root to leaf paths
+  var paths = rootToLeaf(tree);
+  var stemmedRevs;
+
+  var result;
+  for (var i = 0, len = paths.length; i < len; i++) {
+    // Then for each path, we cut off the start of the path based on the
+    // `depth` to stem to, and generate a new set of flat trees
+    var path = paths[i];
+    var stemmed = path.ids;
+    var node;
+    if (stemmed.length > depth) {
+      // only do the stemming work if we actually need to stem
+      if (!stemmedRevs) {
+        stemmedRevs = {}; // avoid allocating this object unnecessarily
+      }
+      var numStemmed = stemmed.length - depth;
+      node = {
+        pos: path.pos + numStemmed,
+        ids: pathToTree(stemmed, numStemmed)
+      };
+
+      for (var s = 0; s < numStemmed; s++) {
+        var rev = (path.pos + s) + '-' + stemmed[s].id;
+        stemmedRevs[rev] = true;
+      }
+    } else { // no need to actually stem
+      node = {
+        pos: path.pos,
+        ids: pathToTree(stemmed, 0)
+      };
+    }
+
+    // Then we remerge all those flat trees together, ensuring that we dont
+    // connect trees that would go beyond the depth limit
+    if (result) {
+      result = doMerge(result, node, true).tree;
+    } else {
+      result = [node];
+    }
+  }
+
+  // this is memory-heavy per Chrome profiler, avoid unless we actually stemmed
+  if (stemmedRevs) {
+    traverseRevTree(result, function (isLeaf, pos, revHash) {
+      // some revisions may have been removed in a branch but not in another
+      delete stemmedRevs[pos + '-' + revHash];
+    });
+  }
+
+  return {
+    tree: result,
+    revs: stemmedRevs ? Object.keys(stemmedRevs) : []
+  };
+}
+
+function merge(tree, path, depth) {
+  var newTree = doMerge(tree, path);
+  var stemmed = stem(newTree.tree, depth);
+  return {
+    tree: stemmed.tree,
+    stemmedRevs: stemmed.revs,
+    conflicts: newTree.conflicts
+  };
+}
+
+// return true if a rev exists in the rev tree, false otherwise
+function revExists(revs, rev) {
+  var toVisit = revs.slice();
+  var splitRev = rev.split('-');
+  var targetPos = parseInt(splitRev[0], 10);
+  var targetId = splitRev[1];
+
+  var node;
+  while ((node = toVisit.pop())) {
+    if (node.pos === targetPos && node.ids[0] === targetId) {
+      return true;
+    }
+    var branches = node.ids[2];
+    for (var i = 0, len = branches.length; i < len; i++) {
+      toVisit.push({pos: node.pos + 1, ids: branches[i]});
+    }
+  }
+  return false;
+}
+
+function getTrees(node) {
+  return node.ids;
+}
+
+// check if a specific revision of a doc has been deleted
+//  - metadata: the metadata object from the doc store
+//  - rev: (optional) the revision to check. defaults to winning revision
+function isDeleted(metadata, rev) {
+  if (!rev) {
+    rev = winningRev(metadata);
+  }
+  var id = rev.substring(rev.indexOf('-') + 1);
+  var toVisit = metadata.rev_tree.map(getTrees);
+
+  var tree;
+  while ((tree = toVisit.pop())) {
+    if (tree[0] === id) {
+      return !!tree[1].deleted;
+    }
+    toVisit = toVisit.concat(tree[2]);
+  }
+}
+
+function isLocalId(id) {
+  return (/^_local/).test(id);
+}
+
+// returns the current leaf node for a given revision
+function latest(rev, metadata) {
+  var toVisit = metadata.rev_tree.slice();
+  var node;
+  while ((node = toVisit.pop())) {
+    var pos = node.pos;
+    var tree = node.ids;
+    var id = tree[0];
+    var opts = tree[1];
+    var branches = tree[2];
+    var isLeaf = branches.length === 0;
+
+    var history = node.history ? node.history.slice() : [];
+    history.push({id: id, pos: pos, opts: opts});
+
+    if (isLeaf) {
+      for (var i = 0, len = history.length; i < len; i++) {
+        var historyNode = history[i];
+        var historyRev = historyNode.pos + '-' + historyNode.id;
+
+        if (historyRev === rev) {
+          // return the rev of this leaf
+          return pos + '-' + id;
+        }
+      }
+    }
+
+    for (var j = 0, l = branches.length; j < l; j++) {
+      toVisit.push({pos: pos + 1, ids: branches[j], history: history});
+    }
+  }
+
+  /* istanbul ignore next */
+  throw new Error('Unable to resolve latest revision for id ' + metadata.id + ', rev ' + rev);
+}
+
+inherits(Changes$1, events.EventEmitter);
+
+function tryCatchInChangeListener(self, change, pending, lastSeq) {
+  // isolate try/catches to avoid V8 deoptimizations
+  try {
+    self.emit('change', change, pending, lastSeq);
+  } catch (e) {
+    guardedConsole('error', 'Error in .on("change", function):', e);
+  }
+}
+
+function Changes$1(db, opts, callback) {
+  events.EventEmitter.call(this);
+  var self = this;
+  this.db = db;
+  opts = opts ? clone(opts) : {};
+  var complete = opts.complete = once(function (err, resp) {
+    if (err) {
+      if (listenerCount(self, 'error') > 0) {
+        self.emit('error', err);
+      }
+    } else {
+      self.emit('complete', resp);
+    }
+    self.removeAllListeners();
+    db.removeListener('destroyed', onDestroy);
+  });
+  if (callback) {
+    self.on('complete', function (resp) {
+      callback(null, resp);
+    });
+    self.on('error', callback);
+  }
+  function onDestroy() {
+    self.cancel();
+  }
+  db.once('destroyed', onDestroy);
+
+  opts.onChange = function (change, pending, lastSeq) {
+    /* istanbul ignore if */
+    if (self.isCancelled) {
+      return;
+    }
+    tryCatchInChangeListener(self, change, pending, lastSeq);
+  };
+
+  var promise = new Promise(function (fulfill, reject) {
+    opts.complete = function (err, res) {
+      if (err) {
+        reject(err);
+      } else {
+        fulfill(res);
+      }
+    };
+  });
+  self.once('cancel', function () {
+    db.removeListener('destroyed', onDestroy);
+    opts.complete(null, {status: 'cancelled'});
+  });
+  this.then = promise.then.bind(promise);
+  this['catch'] = promise['catch'].bind(promise);
+  this.then(function (result) {
+    complete(null, result);
+  }, complete);
+
+
+
+  if (!db.taskqueue.isReady) {
+    db.taskqueue.addTask(function (failed) {
+      if (failed) {
+        opts.complete(failed);
+      } else if (self.isCancelled) {
+        self.emit('cancel');
+      } else {
+        self.validateChanges(opts);
+      }
+    });
+  } else {
+    self.validateChanges(opts);
+  }
+}
+Changes$1.prototype.cancel = function () {
+  this.isCancelled = true;
+  if (this.db.taskqueue.isReady) {
+    this.emit('cancel');
+  }
+};
+function processChange(doc, metadata, opts) {
+  var changeList = [{rev: doc._rev}];
+  if (opts.style === 'all_docs') {
+    changeList = collectLeaves(metadata.rev_tree)
+    .map(function (x) { return {rev: x.rev}; });
+  }
+  var change = {
+    id: metadata.id,
+    changes: changeList,
+    doc: doc
+  };
+
+  if (isDeleted(metadata, doc._rev)) {
+    change.deleted = true;
+  }
+  if (opts.conflicts) {
+    change.doc._conflicts = collectConflicts(metadata);
+    if (!change.doc._conflicts.length) {
+      delete change.doc._conflicts;
+    }
+  }
+  return change;
+}
+
+Changes$1.prototype.validateChanges = function (opts) {
+  var callback = opts.complete;
+  var self = this;
+
+  /* istanbul ignore else */
+  if (PouchDB._changesFilterPlugin) {
+    PouchDB._changesFilterPlugin.validate(opts, function (err) {
+      if (err) {
+        return callback(err);
+      }
+      self.doChanges(opts);
+    });
+  } else {
+    self.doChanges(opts);
+  }
+};
+
+Changes$1.prototype.doChanges = function (opts) {
+  var self = this;
+  var callback = opts.complete;
+
+  opts = clone(opts);
+  if ('live' in opts && !('continuous' in opts)) {
+    opts.continuous = opts.live;
+  }
+  opts.processChange = processChange;
+
+  if (opts.since === 'latest') {
+    opts.since = 'now';
+  }
+  if (!opts.since) {
+    opts.since = 0;
+  }
+  if (opts.since === 'now') {
+    this.db.info().then(function (info) {
+      /* istanbul ignore if */
+      if (self.isCancelled) {
+        callback(null, {status: 'cancelled'});
+        return;
+      }
+      opts.since = info.update_seq;
+      self.doChanges(opts);
+    }, callback);
+    return;
+  }
+
+  /* istanbul ignore else */
+  if (PouchDB._changesFilterPlugin) {
+    PouchDB._changesFilterPlugin.normalize(opts);
+    if (PouchDB._changesFilterPlugin.shouldFilter(this, opts)) {
+      return PouchDB._changesFilterPlugin.filter(this, opts);
+    }
+  } else {
+    ['doc_ids', 'filter', 'selector', 'view'].forEach(function (key) {
+      if (key in opts) {
+        guardedConsole('warn',
+          'The "' + key + '" option was passed in to changes/replicate, ' +
+          'but pouchdb-changes-filter plugin is not installed, so it ' +
+          'was ignored. Please install the plugin to enable filtering.'
+        );
+      }
+    });
+  }
+
+  if (!('descending' in opts)) {
+    opts.descending = false;
+  }
+
+  // 0 and 1 should return 1 document
+  opts.limit = opts.limit === 0 ? 1 : opts.limit;
+  opts.complete = callback;
+  var newPromise = this.db._changes(opts);
+  /* istanbul ignore else */
+  if (newPromise && typeof newPromise.cancel === 'function') {
+    var cancel = self.cancel;
+    self.cancel = getArguments(function (args) {
+      newPromise.cancel();
+      cancel.apply(this, args);
+    });
+  }
+};
+
+/*
+ * A generic pouch adapter
+ */
+
+function compare(left, right) {
+  return left < right ? -1 : left > right ? 1 : 0;
+}
+
+// Wrapper for functions that call the bulkdocs api with a single doc,
+// if the first result is an error, return an error
+function yankError(callback, docId) {
+  return function (err, results) {
+    if (err || (results[0] && results[0].error)) {
+      err = err || results[0];
+      err.docId = docId;
+      callback(err);
+    } else {
+      callback(null, results.length ? results[0]  : results);
+    }
+  };
+}
+
+// clean docs given to us by the user
+function cleanDocs(docs) {
+  for (var i = 0; i < docs.length; i++) {
+    var doc = docs[i];
+    if (doc._deleted) {
+      delete doc._attachments; // ignore atts for deleted docs
+    } else if (doc._attachments) {
+      // filter out extraneous keys from _attachments
+      var atts = Object.keys(doc._attachments);
+      for (var j = 0; j < atts.length; j++) {
+        var att = atts[j];
+        doc._attachments[att] = pick(doc._attachments[att],
+          ['data', 'digest', 'content_type', 'length', 'revpos', 'stub']);
+      }
+    }
+  }
+}
+
+// compare two docs, first by _id then by _rev
+function compareByIdThenRev(a, b) {
+  var idCompare = compare(a._id, b._id);
+  if (idCompare !== 0) {
+    return idCompare;
+  }
+  var aStart = a._revisions ? a._revisions.start : 0;
+  var bStart = b._revisions ? b._revisions.start : 0;
+  return compare(aStart, bStart);
+}
+
+// for every node in a revision tree computes its distance from the closest
+// leaf
+function computeHeight(revs) {
+  var height = {};
+  var edges = [];
+  traverseRevTree(revs, function (isLeaf, pos, id, prnt) {
+    var rev$$1 = pos + "-" + id;
+    if (isLeaf) {
+      height[rev$$1] = 0;
+    }
+    if (prnt !== undefined) {
+      edges.push({from: prnt, to: rev$$1});
+    }
+    return rev$$1;
+  });
+
+  edges.reverse();
+  edges.forEach(function (edge) {
+    if (height[edge.from] === undefined) {
+      height[edge.from] = 1 + height[edge.to];
+    } else {
+      height[edge.from] = Math.min(height[edge.from], 1 + height[edge.to]);
+    }
+  });
+  return height;
+}
+
+function allDocsKeysParse(opts) {
+  var keys =  ('limit' in opts) ?
+    opts.keys.slice(opts.skip, opts.limit + opts.skip) :
+    (opts.skip > 0) ? opts.keys.slice(opts.skip) : opts.keys;
+  opts.keys = keys;
+  opts.skip = 0;
+  delete opts.limit;
+  if (opts.descending) {
+    keys.reverse();
+    opts.descending = false;
+  }
+}
+
+// all compaction is done in a queue, to avoid attaching
+// too many listeners at once
+function doNextCompaction(self) {
+  var task = self._compactionQueue[0];
+  var opts = task.opts;
+  var callback = task.callback;
+  self.get('_local/compaction')["catch"](function () {
+    return false;
+  }).then(function (doc) {
+    if (doc && doc.last_seq) {
+      opts.last_seq = doc.last_seq;
+    }
+    self._compact(opts, function (err, res) {
+      /* istanbul ignore if */
+      if (err) {
+        callback(err);
+      } else {
+        callback(null, res);
+      }
+      immediate(function () {
+        self._compactionQueue.shift();
+        if (self._compactionQueue.length) {
+          doNextCompaction(self);
+        }
+      });
+    });
+  });
+}
+
+function attachmentNameError(name) {
+  if (name.charAt(0) === '_') {
+    return name + ' is not a valid attachment name, attachment ' +
+      'names cannot start with \'_\'';
+  }
+  return false;
+}
+
+inherits(AbstractPouchDB, events.EventEmitter);
+
+function AbstractPouchDB() {
+  events.EventEmitter.call(this);
+
+  // re-bind prototyped methods
+  for (var p in AbstractPouchDB.prototype) {
+    if (typeof this[p] === 'function') {
+      this[p] = this[p].bind(this);
+    }
+  }
+}
+
+AbstractPouchDB.prototype.post =
+  adapterFun('post', function (doc, opts, callback) {
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+  if (typeof doc !== 'object' || Array.isArray(doc)) {
+    return callback(createError(NOT_AN_OBJECT));
+  }
+  this.bulkDocs({docs: [doc]}, opts, yankError(callback, doc._id));
+});
+
+AbstractPouchDB.prototype.put = adapterFun('put', function (doc, opts, cb) {
+  if (typeof opts === 'function') {
+    cb = opts;
+    opts = {};
+  }
+  if (typeof doc !== 'object' || Array.isArray(doc)) {
+    return cb(createError(NOT_AN_OBJECT));
+  }
+  invalidIdError(doc._id);
+  if (isLocalId(doc._id) && typeof this._putLocal === 'function') {
+    if (doc._deleted) {
+      return this._removeLocal(doc, cb);
+    } else {
+      return this._putLocal(doc, cb);
+    }
+  }
+  var self = this;
+  if (opts.force && doc._rev) {
+    transformForceOptionToNewEditsOption();
+    putDoc(function (err) {
+      var result = err ? null : {ok: true, id: doc._id, rev: doc._rev};
+      cb(err, result);
+    });
+  } else {
+    putDoc(cb);
+  }
+
+  function transformForceOptionToNewEditsOption() {
+    var parts = doc._rev.split('-');
+    var oldRevId = parts[1];
+    var oldRevNum = parseInt(parts[0], 10);
+
+    var newRevNum = oldRevNum + 1;
+    var newRevId = rev();
+
+    doc._revisions = {
+      start: newRevNum,
+      ids: [newRevId, oldRevId]
+    };
+    doc._rev = newRevNum + '-' + newRevId;
+    opts.new_edits = false;
+  }
+  function putDoc(next) {
+    if (typeof self._put === 'function' && opts.new_edits !== false) {
+      self._put(doc, opts, next);
+    } else {
+      self.bulkDocs({docs: [doc]}, opts, yankError(next, doc._id));
+    }
+  }
+});
+
+AbstractPouchDB.prototype.putAttachment =
+  adapterFun('putAttachment', function (docId, attachmentId, rev$$1,
+                                              blob, type) {
+  var api = this;
+  if (typeof type === 'function') {
+    type = blob;
+    blob = rev$$1;
+    rev$$1 = null;
+  }
+  // Lets fix in https://github.com/pouchdb/pouchdb/issues/3267
+  /* istanbul ignore if */
+  if (typeof type === 'undefined') {
+    type = blob;
+    blob = rev$$1;
+    rev$$1 = null;
+  }
+  if (!type) {
+    guardedConsole('warn', 'Attachment', attachmentId, 'on document', docId, 'is missing content_type');
+  }
+
+  function createAttachment(doc) {
+    var prevrevpos = '_rev' in doc ? parseInt(doc._rev, 10) : 0;
+    doc._attachments = doc._attachments || {};
+    doc._attachments[attachmentId] = {
+      content_type: type,
+      data: blob,
+      revpos: ++prevrevpos
+    };
+    return api.put(doc);
+  }
+
+  return api.get(docId).then(function (doc) {
+    if (doc._rev !== rev$$1) {
+      throw createError(REV_CONFLICT);
+    }
+
+    return createAttachment(doc);
+  }, function (err) {
+     // create new doc
+    /* istanbul ignore else */
+    if (err.reason === MISSING_DOC.message) {
+      return createAttachment({_id: docId});
+    } else {
+      throw err;
+    }
+  });
+});
+
+AbstractPouchDB.prototype.removeAttachment =
+  adapterFun('removeAttachment', function (docId, attachmentId, rev$$1,
+                                                 callback) {
+  var self = this;
+  self.get(docId, function (err, obj) {
+    /* istanbul ignore if */
+    if (err) {
+      callback(err);
+      return;
+    }
+    if (obj._rev !== rev$$1) {
+      callback(createError(REV_CONFLICT));
+      return;
+    }
+    /* istanbul ignore if */
+    if (!obj._attachments) {
+      return callback();
+    }
+    delete obj._attachments[attachmentId];
+    if (Object.keys(obj._attachments).length === 0) {
+      delete obj._attachments;
+    }
+    self.put(obj, callback);
+  });
+});
+
+AbstractPouchDB.prototype.remove =
+  adapterFun('remove', function (docOrId, optsOrRev, opts, callback) {
+  var doc;
+  if (typeof optsOrRev === 'string') {
+    // id, rev, opts, callback style
+    doc = {
+      _id: docOrId,
+      _rev: optsOrRev
+    };
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+  } else {
+    // doc, opts, callback style
+    doc = docOrId;
+    if (typeof optsOrRev === 'function') {
+      callback = optsOrRev;
+      opts = {};
+    } else {
+      callback = opts;
+      opts = optsOrRev;
+    }
+  }
+  opts = opts || {};
+  opts.was_delete = true;
+  var newDoc = {_id: doc._id, _rev: (doc._rev || opts.rev)};
+  newDoc._deleted = true;
+  if (isLocalId(newDoc._id) && typeof this._removeLocal === 'function') {
+    return this._removeLocal(doc, callback);
+  }
+  this.bulkDocs({docs: [newDoc]}, opts, yankError(callback, newDoc._id));
+});
+
+AbstractPouchDB.prototype.revsDiff =
+  adapterFun('revsDiff', function (req, opts, callback) {
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+  var ids = Object.keys(req);
+
+  if (!ids.length) {
+    return callback(null, {});
+  }
+
+  var count = 0;
+  var missing = new ExportedMap();
+
+  function addToMissing(id, revId) {
+    if (!missing.has(id)) {
+      missing.set(id, {missing: []});
+    }
+    missing.get(id).missing.push(revId);
+  }
+
+  function processDoc(id, rev_tree) {
+    // Is this fast enough? Maybe we should switch to a set simulated by a map
+    var missingForId = req[id].slice(0);
+    traverseRevTree(rev_tree, function (isLeaf, pos, revHash, ctx,
+      opts) {
+        var rev$$1 = pos + '-' + revHash;
+        var idx = missingForId.indexOf(rev$$1);
+        if (idx === -1) {
+          return;
+        }
+
+        missingForId.splice(idx, 1);
+        /* istanbul ignore if */
+        if (opts.status !== 'available') {
+          addToMissing(id, rev$$1);
+        }
+      });
+
+    // Traversing the tree is synchronous, so now `missingForId` contains
+    // revisions that were not found in the tree
+    missingForId.forEach(function (rev$$1) {
+      addToMissing(id, rev$$1);
+    });
+  }
+
+  ids.map(function (id) {
+    this._getRevisionTree(id, function (err, rev_tree) {
+      if (err && err.status === 404 && err.message === 'missing') {
+        missing.set(id, {missing: req[id]});
+      } else if (err) {
+        /* istanbul ignore next */
+        return callback(err);
+      } else {
+        processDoc(id, rev_tree);
+      }
+
+      if (++count === ids.length) {
+        // convert LazyMap to object
+        var missingObj = {};
+        missing.forEach(function (value, key) {
+          missingObj[key] = value;
+        });
+        return callback(null, missingObj);
+      }
+    });
+  }, this);
+});
+
+// _bulk_get API for faster replication, as described in
+// https://github.com/apache/couchdb-chttpd/pull/33
+// At the "abstract" level, it will just run multiple get()s in
+// parallel, because this isn't much of a performance cost
+// for local databases (except the cost of multiple transactions, which is
+// small). The http adapter overrides this in order
+// to do a more efficient single HTTP request.
+AbstractPouchDB.prototype.bulkGet =
+  adapterFun('bulkGet', function (opts, callback) {
+  bulkGet(this, opts, callback);
+});
+
+// compact one document and fire callback
+// by compacting we mean removing all revisions which
+// are further from the leaf in revision tree than max_height
+AbstractPouchDB.prototype.compactDocument =
+  adapterFun('compactDocument', function (docId, maxHeight, callback) {
+  var self = this;
+  this._getRevisionTree(docId, function (err, revTree) {
+    /* istanbul ignore if */
+    if (err) {
+      return callback(err);
+    }
+    var height = computeHeight(revTree);
+    var candidates = [];
+    var revs = [];
+    Object.keys(height).forEach(function (rev$$1) {
+      if (height[rev$$1] > maxHeight) {
+        candidates.push(rev$$1);
+      }
+    });
+
+    traverseRevTree(revTree, function (isLeaf, pos, revHash, ctx, opts) {
+      var rev$$1 = pos + '-' + revHash;
+      if (opts.status === 'available' && candidates.indexOf(rev$$1) !== -1) {
+        revs.push(rev$$1);
+      }
+    });
+    self._doCompaction(docId, revs, callback);
+  });
+});
+
+// compact the whole database using single document
+// compaction
+AbstractPouchDB.prototype.compact =
+  adapterFun('compact', function (opts, callback) {
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+
+  var self = this;
+  opts = opts || {};
+
+  self._compactionQueue = self._compactionQueue || [];
+  self._compactionQueue.push({opts: opts, callback: callback});
+  if (self._compactionQueue.length === 1) {
+    doNextCompaction(self);
+  }
+});
+AbstractPouchDB.prototype._compact = function (opts, callback) {
+  var self = this;
+  var changesOpts = {
+    return_docs: false,
+    last_seq: opts.last_seq || 0
+  };
+  var promises = [];
+
+  function onChange(row) {
+    promises.push(self.compactDocument(row.id, 0));
+  }
+  function onComplete(resp) {
+    var lastSeq = resp.last_seq;
+    Promise.all(promises).then(function () {
+      return upsert(self, '_local/compaction', function deltaFunc(doc) {
+        if (!doc.last_seq || doc.last_seq < lastSeq) {
+          doc.last_seq = lastSeq;
+          return doc;
+        }
+        return false; // somebody else got here first, don't update
+      });
+    }).then(function () {
+      callback(null, {ok: true});
+    })["catch"](callback);
+  }
+  self.changes(changesOpts)
+    .on('change', onChange)
+    .on('complete', onComplete)
+    .on('error', callback);
+};
+
+/* Begin api wrappers. Specific functionality to storage belongs in the
+   _[method] */
+AbstractPouchDB.prototype.get = adapterFun('get', function (id, opts, cb) {
+  if (typeof opts === 'function') {
+    cb = opts;
+    opts = {};
+  }
+  if (typeof id !== 'string') {
+    return cb(createError(INVALID_ID));
+  }
+  if (isLocalId(id) && typeof this._getLocal === 'function') {
+    return this._getLocal(id, cb);
+  }
+  var leaves = [], self = this;
+
+  function finishOpenRevs() {
+    var result = [];
+    var count = leaves.length;
+    /* istanbul ignore if */
+    if (!count) {
+      return cb(null, result);
+    }
+
+    // order with open_revs is unspecified
+    leaves.forEach(function (leaf) {
+      self.get(id, {
+        rev: leaf,
+        revs: opts.revs,
+        latest: opts.latest,
+        attachments: opts.attachments,
+        binary: opts.binary
+      }, function (err, doc) {
+        if (!err) {
+          // using latest=true can produce duplicates
+          var existing;
+          for (var i = 0, l = result.length; i < l; i++) {
+            if (result[i].ok && result[i].ok._rev === doc._rev) {
+              existing = true;
+              break;
+            }
+          }
+          if (!existing) {
+            result.push({ok: doc});
+          }
+        } else {
+          result.push({missing: leaf});
+        }
+        count--;
+        if (!count) {
+          cb(null, result);
+        }
+      });
+    });
+  }
+
+  if (opts.open_revs) {
+    if (opts.open_revs === "all") {
+      this._getRevisionTree(id, function (err, rev_tree) {
+        /* istanbul ignore if */
+        if (err) {
+          return cb(err);
+        }
+        leaves = collectLeaves(rev_tree).map(function (leaf) {
+          return leaf.rev;
+        });
+        finishOpenRevs();
+      });
+    } else {
+      if (Array.isArray(opts.open_revs)) {
+        leaves = opts.open_revs;
+        for (var i = 0; i < leaves.length; i++) {
+          var l = leaves[i];
+          // looks like it's the only thing couchdb checks
+          if (!(typeof (l) === "string" && /^\d+-/.test(l))) {
+            return cb(createError(INVALID_REV));
+          }
+        }
+        finishOpenRevs();
+      } else {
+        return cb(createError(UNKNOWN_ERROR, 'function_clause'));
+      }
+    }
+    return; // open_revs does not like other options
+  }
+
+  return this._get(id, opts, function (err, result) {
+    if (err) {
+      err.docId = id;
+      return cb(err);
+    }
+
+    var doc = result.doc;
+    var metadata = result.metadata;
+    var ctx = result.ctx;
+
+    if (opts.conflicts) {
+      var conflicts = collectConflicts(metadata);
+      if (conflicts.length) {
+        doc._conflicts = conflicts;
+      }
+    }
+
+    if (isDeleted(metadata, doc._rev)) {
+      doc._deleted = true;
+    }
+
+    if (opts.revs || opts.revs_info) {
+      var splittedRev = doc._rev.split('-');
+      var revNo       = parseInt(splittedRev[0], 10);
+      var revHash     = splittedRev[1];
+
+      var paths = rootToLeaf(metadata.rev_tree);
+      var path = null;
+
+      for (var i = 0; i < paths.length; i++) {
+        var currentPath = paths[i];
+        var hashIndex = currentPath.ids.map(function (x) { return x.id; })
+          .indexOf(revHash);
+        var hashFoundAtRevPos = hashIndex === (revNo - 1);
+
+        if (hashFoundAtRevPos || (!path && hashIndex !== -1)) {
+          path = currentPath;
+        }
+      }
+
+      /* istanbul ignore if */
+      if (!path) {
+        err = new Error('invalid rev tree');
+        err.docId = id;
+        return cb(err);
+      }
+
+      var indexOfRev = path.ids.map(function (x) { return x.id; })
+        .indexOf(doc._rev.split('-')[1]) + 1;
+      var howMany = path.ids.length - indexOfRev;
+      path.ids.splice(indexOfRev, howMany);
+      path.ids.reverse();
+
+      if (opts.revs) {
+        doc._revisions = {
+          start: (path.pos + path.ids.length) - 1,
+          ids: path.ids.map(function (rev$$1) {
+            return rev$$1.id;
+          })
+        };
+      }
+      if (opts.revs_info) {
+        var pos =  path.pos + path.ids.length;
+        doc._revs_info = path.ids.map(function (rev$$1) {
+          pos--;
+          return {
+            rev: pos + '-' + rev$$1.id,
+            status: rev$$1.opts.status
+          };
+        });
+      }
+    }
+
+    if (opts.attachments && doc._attachments) {
+      var attachments = doc._attachments;
+      var count = Object.keys(attachments).length;
+      if (count === 0) {
+        return cb(null, doc);
+      }
+      Object.keys(attachments).forEach(function (key) {
+        this._getAttachment(doc._id, key, attachments[key], {
+          // Previously the revision handling was done in adapter.js
+          // getAttachment, however since idb-next doesnt we need to
+          // pass the rev through
+          rev: doc._rev,
+          binary: opts.binary,
+          ctx: ctx
+        }, function (err, data) {
+          var att = doc._attachments[key];
+          att.data = data;
+          delete att.stub;
+          delete att.length;
+          if (!--count) {
+            cb(null, doc);
+          }
+        });
+      }, self);
+    } else {
+      if (doc._attachments) {
+        for (var key in doc._attachments) {
+          /* istanbul ignore else */
+          if (doc._attachments.hasOwnProperty(key)) {
+            doc._attachments[key].stub = true;
+          }
+        }
+      }
+      cb(null, doc);
+    }
+  });
+});
+
+// TODO: I dont like this, it forces an extra read for every
+// attachment read and enforces a confusing api between
+// adapter.js and the adapter implementation
+AbstractPouchDB.prototype.getAttachment =
+  adapterFun('getAttachment', function (docId, attachmentId, opts, callback) {
+  var self = this;
+  if (opts instanceof Function) {
+    callback = opts;
+    opts = {};
+  }
+  this._get(docId, opts, function (err, res) {
+    if (err) {
+      return callback(err);
+    }
+    if (res.doc._attachments && res.doc._attachments[attachmentId]) {
+      opts.ctx = res.ctx;
+      opts.binary = true;
+      self._getAttachment(docId, attachmentId,
+                          res.doc._attachments[attachmentId], opts, callback);
+    } else {
+      return callback(createError(MISSING_DOC));
+    }
+  });
+});
+
+AbstractPouchDB.prototype.allDocs =
+  adapterFun('allDocs', function (opts, callback) {
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+  opts.skip = typeof opts.skip !== 'undefined' ? opts.skip : 0;
+  if (opts.start_key) {
+    opts.startkey = opts.start_key;
+  }
+  if (opts.end_key) {
+    opts.endkey = opts.end_key;
+  }
+  if ('keys' in opts) {
+    if (!Array.isArray(opts.keys)) {
+      return callback(new TypeError('options.keys must be an array'));
+    }
+    var incompatibleOpt =
+      ['startkey', 'endkey', 'key'].filter(function (incompatibleOpt) {
+      return incompatibleOpt in opts;
+    })[0];
+    if (incompatibleOpt) {
+      callback(createError(QUERY_PARSE_ERROR,
+        'Query parameter `' + incompatibleOpt +
+        '` is not compatible with multi-get'
+      ));
+      return;
+    }
+    if (!isRemote(this)) {
+      allDocsKeysParse(opts);
+      if (opts.keys.length === 0) {
+        return this._allDocs({limit: 0}, callback);
+      }
+    }
+  }
+
+  return this._allDocs(opts, callback);
+});
+
+AbstractPouchDB.prototype.changes = function (opts, callback) {
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+
+  opts = opts || {};
+
+  // By default set return_docs to false if the caller has opts.live = true,
+  // this will prevent us from collecting the set of changes indefinitely
+  // resulting in growing memory
+  opts.return_docs = ('return_docs' in opts) ? opts.return_docs : !opts.live;
+
+  return new Changes$1(this, opts, callback);
+};
+
+AbstractPouchDB.prototype.close = adapterFun('close', function (callback) {
+  this._closed = true;
+  this.emit('closed');
+  return this._close(callback);
+});
+
+AbstractPouchDB.prototype.info = adapterFun('info', function (callback) {
+  var self = this;
+  this._info(function (err, info) {
+    if (err) {
+      return callback(err);
+    }
+    // assume we know better than the adapter, unless it informs us
+    info.db_name = info.db_name || self.name;
+    info.auto_compaction = !!(self.auto_compaction && !isRemote(self));
+    info.adapter = self.adapter;
+    callback(null, info);
+  });
+});
+
+AbstractPouchDB.prototype.id = adapterFun('id', function (callback) {
+  return this._id(callback);
+});
+
+/* istanbul ignore next */
+AbstractPouchDB.prototype.type = function () {
+  return (typeof this._type === 'function') ? this._type() : this.adapter;
+};
+
+AbstractPouchDB.prototype.bulkDocs =
+  adapterFun('bulkDocs', function (req, opts, callback) {
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+
+  opts = opts || {};
+
+  if (Array.isArray(req)) {
+    req = {
+      docs: req
+    };
+  }
+
+  if (!req || !req.docs || !Array.isArray(req.docs)) {
+    return callback(createError(MISSING_BULK_DOCS));
+  }
+
+  for (var i = 0; i < req.docs.length; ++i) {
+    if (typeof req.docs[i] !== 'object' || Array.isArray(req.docs[i])) {
+      return callback(createError(NOT_AN_OBJECT));
+    }
+  }
+
+  var attachmentError;
+  req.docs.forEach(function (doc) {
+    if (doc._attachments) {
+      Object.keys(doc._attachments).forEach(function (name) {
+        attachmentError = attachmentError || attachmentNameError(name);
+        if (!doc._attachments[name].content_type) {
+          guardedConsole('warn', 'Attachment', name, 'on document', doc._id, 'is missing content_type');
+        }
+      });
+    }
+  });
+
+  if (attachmentError) {
+    return callback(createError(BAD_REQUEST, attachmentError));
+  }
+
+  if (!('new_edits' in opts)) {
+    if ('new_edits' in req) {
+      opts.new_edits = req.new_edits;
+    } else {
+      opts.new_edits = true;
+    }
+  }
+
+  var adapter = this;
+  if (!opts.new_edits && !isRemote(adapter)) {
+    // ensure revisions of the same doc are sorted, so that
+    // the local adapter processes them correctly (#2935)
+    req.docs.sort(compareByIdThenRev);
+  }
+
+  cleanDocs(req.docs);
+
+  // in the case of conflicts, we want to return the _ids to the user
+  // however, the underlying adapter may destroy the docs array, so
+  // create a copy here
+  var ids = req.docs.map(function (doc) {
+    return doc._id;
+  });
+
+  return this._bulkDocs(req, opts, function (err, res) {
+    if (err) {
+      return callback(err);
+    }
+    if (!opts.new_edits) {
+      // this is what couch does when new_edits is false
+      res = res.filter(function (x) {
+        return x.error;
+      });
+    }
+    // add ids for error/conflict responses (not required for CouchDB)
+    if (!isRemote(adapter)) {
+      for (var i = 0, l = res.length; i < l; i++) {
+        res[i].id = res[i].id || ids[i];
+      }
+    }
+
+    callback(null, res);
+  });
+});
+
+AbstractPouchDB.prototype.registerDependentDatabase =
+  adapterFun('registerDependentDatabase', function (dependentDb,
+                                                          callback) {
+  var depDB = new this.constructor(dependentDb, this.__opts);
+
+  function diffFun(doc) {
+    doc.dependentDbs = doc.dependentDbs || {};
+    if (doc.dependentDbs[dependentDb]) {
+      return false; // no update required
+    }
+    doc.dependentDbs[dependentDb] = true;
+    return doc;
+  }
+  upsert(this, '_local/_pouch_dependentDbs', diffFun)
+    .then(function () {
+      callback(null, {db: depDB});
+    })["catch"](callback);
+});
+
+AbstractPouchDB.prototype.destroy =
+  adapterFun('destroy', function (opts, callback) {
+
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+
+  var self = this;
+  var usePrefix = 'use_prefix' in self ? self.use_prefix : true;
+
+  function destroyDb() {
+    // call destroy method of the particular adaptor
+    self._destroy(opts, function (err, resp) {
+      if (err) {
+        return callback(err);
+      }
+      self._destroyed = true;
+      self.emit('destroyed');
+      callback(null, resp || { 'ok': true });
+    });
+  }
+
+  if (isRemote(self)) {
+    // no need to check for dependent DBs if it's a remote DB
+    return destroyDb();
+  }
+
+  self.get('_local/_pouch_dependentDbs', function (err, localDoc) {
+    if (err) {
+      /* istanbul ignore if */
+      if (err.status !== 404) {
+        return callback(err);
+      } else { // no dependencies
+        return destroyDb();
+      }
+    }
+    var dependentDbs = localDoc.dependentDbs;
+    var PouchDB = self.constructor;
+    var deletedMap = Object.keys(dependentDbs).map(function (name) {
+      // use_prefix is only false in the browser
+      /* istanbul ignore next */
+      var trueName = usePrefix ?
+        name.replace(new RegExp('^' + PouchDB.prefix), '') : name;
+      return new PouchDB(trueName, self.__opts).destroy();
+    });
+    Promise.all(deletedMap).then(destroyDb, callback);
+  });
+});
+
+function TaskQueue() {
+  this.isReady = false;
+  this.failed = false;
+  this.queue = [];
+}
+
+TaskQueue.prototype.execute = function () {
+  var fun;
+  if (this.failed) {
+    while ((fun = this.queue.shift())) {
+      fun(this.failed);
+    }
+  } else {
+    while ((fun = this.queue.shift())) {
+      fun();
+    }
+  }
+};
+
+TaskQueue.prototype.fail = function (err) {
+  this.failed = err;
+  this.execute();
+};
+
+TaskQueue.prototype.ready = function (db) {
+  this.isReady = true;
+  this.db = db;
+  this.execute();
+};
+
+TaskQueue.prototype.addTask = function (fun) {
+  this.queue.push(fun);
+  if (this.failed) {
+    this.execute();
+  }
+};
+
+function parseAdapter(name, opts) {
+  var match = name.match(/([a-z-]*):\/\/(.*)/);
+  if (match) {
+    // the http adapter expects the fully qualified name
+    return {
+      name: /https?/.test(match[1]) ? match[1] + '://' + match[2] : match[2],
+      adapter: match[1]
+    };
+  }
+
+  var adapters = PouchDB.adapters;
+  var preferredAdapters = PouchDB.preferredAdapters;
+  var prefix = PouchDB.prefix;
+  var adapterName = opts.adapter;
+
+  if (!adapterName) { // automatically determine adapter
+    for (var i = 0; i < preferredAdapters.length; ++i) {
+      adapterName = preferredAdapters[i];
+      // check for browsers that have been upgraded from websql-only to websql+idb
+      /* istanbul ignore if */
+      if (adapterName === 'idb' && 'websql' in adapters &&
+          hasLocalStorage() && localStorage['_pouch__websqldb_' + prefix + name]) {
+        // log it, because this can be confusing during development
+        guardedConsole('log', 'PouchDB is downgrading "' + name + '" to WebSQL to' +
+          ' avoid data loss, because it was already opened with WebSQL.');
+        continue; // keep using websql to avoid user data loss
+      }
+      break;
+    }
+  }
+
+  var adapter = adapters[adapterName];
+
+  // if adapter is invalid, then an error will be thrown later
+  var usePrefix = (adapter && 'use_prefix' in adapter) ?
+    adapter.use_prefix : true;
+
+  return {
+    name: usePrefix ? (prefix + name) : name,
+    adapter: adapterName
+  };
+}
+
+// OK, so here's the deal. Consider this code:
+//     var db1 = new PouchDB('foo');
+//     var db2 = new PouchDB('foo');
+//     db1.destroy();
+// ^ these two both need to emit 'destroyed' events,
+// as well as the PouchDB constructor itself.
+// So we have one db object (whichever one got destroy() called on it)
+// responsible for emitting the initial event, which then gets emitted
+// by the constructor, which then broadcasts it to any other dbs
+// that may have been created with the same name.
+function prepareForDestruction(self) {
+
+  function onDestroyed(from_constructor) {
+    self.removeListener('closed', onClosed);
+    if (!from_constructor) {
+      self.constructor.emit('destroyed', self.name);
+    }
+  }
+
+  function onClosed() {
+    self.removeListener('destroyed', onDestroyed);
+    self.constructor.emit('unref', self);
+  }
+
+  self.once('destroyed', onDestroyed);
+  self.once('closed', onClosed);
+  self.constructor.emit('ref', self);
+}
+
+inherits(PouchDB, AbstractPouchDB);
+function PouchDB(name, opts) {
+  // In Node our test suite only tests this for PouchAlt unfortunately
+  /* istanbul ignore if */
+  if (!(this instanceof PouchDB)) {
+    return new PouchDB(name, opts);
+  }
+
+  var self = this;
+  opts = opts || {};
+
+  if (name && typeof name === 'object') {
+    opts = name;
+    name = opts.name;
+    delete opts.name;
+  }
+
+  if (opts.deterministic_revs === undefined) {
+    opts.deterministic_revs = true;
+  }
+
+  this.__opts = opts = clone(opts);
+
+  self.auto_compaction = opts.auto_compaction;
+  self.prefix = PouchDB.prefix;
+
+  if (typeof name !== 'string') {
+    throw new Error('Missing/invalid DB name');
+  }
+
+  var prefixedName = (opts.prefix || '') + name;
+  var backend = parseAdapter(prefixedName, opts);
+
+  opts.name = backend.name;
+  opts.adapter = opts.adapter || backend.adapter;
+
+  self.name = name;
+  self._adapter = opts.adapter;
+  PouchDB.emit('debug', ['adapter', 'Picked adapter: ', opts.adapter]);
+
+  if (!PouchDB.adapters[opts.adapter] ||
+      !PouchDB.adapters[opts.adapter].valid()) {
+    throw new Error('Invalid Adapter: ' + opts.adapter);
+  }
+
+  AbstractPouchDB.call(self);
+  self.taskqueue = new TaskQueue();
+
+  self.adapter = opts.adapter;
+
+  PouchDB.adapters[opts.adapter].call(self, opts, function (err) {
+    if (err) {
+      return self.taskqueue.fail(err);
+    }
+    prepareForDestruction(self);
+
+    self.emit('created', self);
+    PouchDB.emit('created', self.name);
+    self.taskqueue.ready(self);
+  });
+
+}
+
+// AbortController was introduced quite a while after fetch and
+// isnt required for PouchDB to function so polyfill if needed
+var a = (typeof AbortController !== 'undefined')
+    ? AbortController
+    : function () { return {abort: function () {}}; };
+
+var f$1 = fetch;
+var h = Headers;
+
+PouchDB.adapters = {};
+PouchDB.preferredAdapters = [];
+
+PouchDB.prefix = '_pouch_';
+
+var eventEmitter = new events.EventEmitter();
+
+function setUpEventEmitter(Pouch) {
+  Object.keys(events.EventEmitter.prototype).forEach(function (key) {
+    if (typeof events.EventEmitter.prototype[key] === 'function') {
+      Pouch[key] = eventEmitter[key].bind(eventEmitter);
+    }
+  });
+
+  // these are created in constructor.js, and allow us to notify each DB with
+  // the same name that it was destroyed, via the constructor object
+  var destructListeners = Pouch._destructionListeners = new ExportedMap();
+
+  Pouch.on('ref', function onConstructorRef(db) {
+    if (!destructListeners.has(db.name)) {
+      destructListeners.set(db.name, []);
+    }
+    destructListeners.get(db.name).push(db);
+  });
+
+  Pouch.on('unref', function onConstructorUnref(db) {
+    if (!destructListeners.has(db.name)) {
+      return;
+    }
+    var dbList = destructListeners.get(db.name);
+    var pos = dbList.indexOf(db);
+    if (pos < 0) {
+      /* istanbul ignore next */
+      return;
+    }
+    dbList.splice(pos, 1);
+    if (dbList.length > 1) {
+      /* istanbul ignore next */
+      destructListeners.set(db.name, dbList);
+    } else {
+      destructListeners["delete"](db.name);
+    }
+  });
+
+  Pouch.on('destroyed', function onConstructorDestroyed(name) {
+    if (!destructListeners.has(name)) {
+      return;
+    }
+    var dbList = destructListeners.get(name);
+    destructListeners["delete"](name);
+    dbList.forEach(function (db) {
+      db.emit('destroyed',true);
+    });
+  });
+}
+
+setUpEventEmitter(PouchDB);
+
+PouchDB.adapter = function (id, obj, addToPreferredAdapters) {
+  /* istanbul ignore else */
+  if (obj.valid()) {
+    PouchDB.adapters[id] = obj;
+    if (addToPreferredAdapters) {
+      PouchDB.preferredAdapters.push(id);
+    }
+  }
+};
+
+PouchDB.plugin = function (obj) {
+  if (typeof obj === 'function') { // function style for plugins
+    obj(PouchDB);
+  } else if (typeof obj !== 'object' || Object.keys(obj).length === 0) {
+    throw new Error('Invalid plugin: got "' + obj + '", expected an object or a function');
+  } else {
+    Object.keys(obj).forEach(function (id) { // object style for plugins
+      PouchDB.prototype[id] = obj[id];
+    });
+  }
+  if (this.__defaults) {
+    PouchDB.__defaults = $inject_Object_assign({}, this.__defaults);
+  }
+  return PouchDB;
+};
+
+PouchDB.defaults = function (defaultOpts) {
+  function PouchAlt(name, opts) {
+    if (!(this instanceof PouchAlt)) {
+      return new PouchAlt(name, opts);
+    }
+
+    opts = opts || {};
+
+    if (name && typeof name === 'object') {
+      opts = name;
+      name = opts.name;
+      delete opts.name;
+    }
+
+    opts = $inject_Object_assign({}, PouchAlt.__defaults, opts);
+    PouchDB.call(this, name, opts);
+  }
+
+  inherits(PouchAlt, PouchDB);
+
+  PouchAlt.preferredAdapters = PouchDB.preferredAdapters.slice();
+  Object.keys(PouchDB).forEach(function (key) {
+    if (!(key in PouchAlt)) {
+      PouchAlt[key] = PouchDB[key];
+    }
+  });
+
+  // make default options transitive
+  // https://github.com/pouchdb/pouchdb/issues/5922
+  PouchAlt.__defaults = $inject_Object_assign({}, this.__defaults, defaultOpts);
+
+  return PouchAlt;
+};
+
+PouchDB.fetch = function (url, opts) {
+  return f$1(url, opts);
+};
+
+// managed automatically by set-version.js
+var version = "7.1.1";
+
+// this would just be "return doc[field]", but fields
+// can be "deep" due to dot notation
+function getFieldFromDoc(doc, parsedField) {
+  var value = doc;
+  for (var i = 0, len = parsedField.length; i < len; i++) {
+    var key = parsedField[i];
+    value = value[key];
+    if (!value) {
+      break;
+    }
+  }
+  return value;
+}
+
+function compare$1(left, right) {
+  return left < right ? -1 : left > right ? 1 : 0;
+}
+
+// Converts a string in dot notation to an array of its components, with backslash escaping
+function parseField(fieldName) {
+  // fields may be deep (e.g. "foo.bar.baz"), so parse
+  var fields = [];
+  var current = '';
+  for (var i = 0, len = fieldName.length; i < len; i++) {
+    var ch = fieldName[i];
+    if (ch === '.') {
+      if (i > 0 && fieldName[i - 1] === '\\') { // escaped delimiter
+        current = current.substring(0, current.length - 1) + '.';
+      } else { // not escaped, so delimiter
+        fields.push(current);
+        current = '';
+      }
+    } else { // normal character
+      current += ch;
+    }
+  }
+  fields.push(current);
+  return fields;
+}
+
+var combinationFields = ['$or', '$nor', '$not'];
+function isCombinationalField(field) {
+  return combinationFields.indexOf(field) > -1;
+}
+
+function getKey(obj) {
+  return Object.keys(obj)[0];
+}
+
+function getValue(obj) {
+  return obj[getKey(obj)];
+}
+
+
+// flatten an array of selectors joined by an $and operator
+function mergeAndedSelectors(selectors) {
+
+  // sort to ensure that e.g. if the user specified
+  // $and: [{$gt: 'a'}, {$gt: 'b'}], then it's collapsed into
+  // just {$gt: 'b'}
+  var res = {};
+
+  selectors.forEach(function (selector) {
+    Object.keys(selector).forEach(function (field) {
+      var matcher = selector[field];
+      if (typeof matcher !== 'object') {
+        matcher = {$eq: matcher};
+      }
+
+      if (isCombinationalField(field)) {
+        if (matcher instanceof Array) {
+          res[field] = matcher.map(function (m) {
+            return mergeAndedSelectors([m]);
+          });
+        } else {
+          res[field] = mergeAndedSelectors([matcher]);
+        }
+      } else {
+        var fieldMatchers = res[field] = res[field] || {};
+        Object.keys(matcher).forEach(function (operator) {
+          var value = matcher[operator];
+
+          if (operator === '$gt' || operator === '$gte') {
+            return mergeGtGte(operator, value, fieldMatchers);
+          } else if (operator === '$lt' || operator === '$lte') {
+            return mergeLtLte(operator, value, fieldMatchers);
+          } else if (operator === '$ne') {
+            return mergeNe(value, fieldMatchers);
+          } else if (operator === '$eq') {
+            return mergeEq(value, fieldMatchers);
+          }
+          fieldMatchers[operator] = value;
+        });
+      }
+    });
+  });
+
+  return res;
+}
+
+
+
+// collapse logically equivalent gt/gte values
+function mergeGtGte(operator, value, fieldMatchers) {
+  if (typeof fieldMatchers.$eq !== 'undefined') {
+    return; // do nothing
+  }
+  if (typeof fieldMatchers.$gte !== 'undefined') {
+    if (operator === '$gte') {
+      if (value > fieldMatchers.$gte) { // more specificity
+        fieldMatchers.$gte = value;
+      }
+    } else { // operator === '$gt'
+      if (value >= fieldMatchers.$gte) { // more specificity
+        delete fieldMatchers.$gte;
+        fieldMatchers.$gt = value;
+      }
+    }
+  } else if (typeof fieldMatchers.$gt !== 'undefined') {
+    if (operator === '$gte') {
+      if (value > fieldMatchers.$gt) { // more specificity
+        delete fieldMatchers.$gt;
+        fieldMatchers.$gte = value;
+      }
+    } else { // operator === '$gt'
+      if (value > fieldMatchers.$gt) { // more specificity
+        fieldMatchers.$gt = value;
+      }
+    }
+  } else {
+    fieldMatchers[operator] = value;
+  }
+}
+
+// collapse logically equivalent lt/lte values
+function mergeLtLte(operator, value, fieldMatchers) {
+  if (typeof fieldMatchers.$eq !== 'undefined') {
+    return; // do nothing
+  }
+  if (typeof fieldMatchers.$lte !== 'undefined') {
+    if (operator === '$lte') {
+      if (value < fieldMatchers.$lte) { // more specificity
+        fieldMatchers.$lte = value;
+      }
+    } else { // operator === '$gt'
+      if (value <= fieldMatchers.$lte) { // more specificity
+        delete fieldMatchers.$lte;
+        fieldMatchers.$lt = value;
+      }
+    }
+  } else if (typeof fieldMatchers.$lt !== 'undefined') {
+    if (operator === '$lte') {
+      if (value < fieldMatchers.$lt) { // more specificity
+        delete fieldMatchers.$lt;
+        fieldMatchers.$lte = value;
+      }
+    } else { // operator === '$gt'
+      if (value < fieldMatchers.$lt) { // more specificity
+        fieldMatchers.$lt = value;
+      }
+    }
+  } else {
+    fieldMatchers[operator] = value;
+  }
+}
+
+// combine $ne values into one array
+function mergeNe(value, fieldMatchers) {
+  if ('$ne' in fieldMatchers) {
+    // there are many things this could "not" be
+    fieldMatchers.$ne.push(value);
+  } else { // doesn't exist yet
+    fieldMatchers.$ne = [value];
+  }
+}
+
+// add $eq into the mix
+function mergeEq(value, fieldMatchers) {
+  // these all have less specificity than the $eq
+  // TODO: check for user errors here
+  delete fieldMatchers.$gt;
+  delete fieldMatchers.$gte;
+  delete fieldMatchers.$lt;
+  delete fieldMatchers.$lte;
+  delete fieldMatchers.$ne;
+  fieldMatchers.$eq = value;
+}
+
+//#7458: execute function mergeAndedSelectors on nested $and
+function mergeAndedSelectorsNested(obj) {
+    for (var prop in obj) {
+        if (Array.isArray(obj)) {
+            for (var i in obj) {
+                if (obj[i]['$and']) {
+                    obj[i] = mergeAndedSelectors(obj[i]['$and']);
+                }
+            }
+        }
+        var value = obj[prop];
+        if (typeof value === 'object') {
+            mergeAndedSelectorsNested(value); // <- recursive call
+        }
+    }
+    return obj;
+}
+
+//#7458: determine id $and is present in selector (at any level)
+function isAndInSelector(obj, isAnd) {
+    for (var prop in obj) {
+        if (prop === '$and') {
+            isAnd = true;
+        }
+        var value = obj[prop];
+        if (typeof value === 'object') {
+            isAnd = isAndInSelector(value, isAnd); // <- recursive call
+        }
+    }
+    return isAnd;
+}
+
+//
+// normalize the selector
+//
+function massageSelector(input) {
+  var result = clone(input);
+  var wasAnded = false;
+    //#7458: if $and is present in selector (at any level) merge nested $and
+    if (isAndInSelector(result, false)) {
+        result = mergeAndedSelectorsNested(result);
+        if ('$and' in result) {
+            result = mergeAndedSelectors(result['$and']);
+        }
+        wasAnded = true;
+    }
+
+  ['$or', '$nor'].forEach(function (orOrNor) {
+    if (orOrNor in result) {
+      // message each individual selector
+      // e.g. {foo: 'bar'} becomes {foo: {$eq: 'bar'}}
+      result[orOrNor].forEach(function (subSelector) {
+        var fields = Object.keys(subSelector);
+        for (var i = 0; i < fields.length; i++) {
+          var field = fields[i];
+          var matcher = subSelector[field];
+          if (typeof matcher !== 'object' || matcher === null) {
+            subSelector[field] = {$eq: matcher};
+          }
+        }
+      });
+    }
+  });
+
+  if ('$not' in result) {
+    //This feels a little like forcing, but it will work for now,
+    //I would like to come back to this and make the merging of selectors a little more generic
+    result['$not'] = mergeAndedSelectors([result['$not']]);
+  }
+
+  var fields = Object.keys(result);
+
+  for (var i = 0; i < fields.length; i++) {
+    var field = fields[i];
+    var matcher = result[field];
+
+    if (typeof matcher !== 'object' || matcher === null) {
+      matcher = {$eq: matcher};
+    } else if ('$ne' in matcher && !wasAnded) {
+      // I put these in an array, since there may be more than one
+      // but in the "mergeAnded" operation, I already take care of that
+      matcher.$ne = [matcher.$ne];
+    }
+    result[field] = matcher;
+  }
+
+  return result;
+}
+
+function pad(str, padWith, upToLength) {
+  var padding = '';
+  var targetLength = upToLength - str.length;
+  /* istanbul ignore next */
+  while (padding.length < targetLength) {
+    padding += padWith;
+  }
+  return padding;
+}
+
+function padLeft(str, padWith, upToLength) {
+  var padding = pad(str, padWith, upToLength);
+  return padding + str;
+}
+
+var MIN_MAGNITUDE = -324; // verified by -Number.MIN_VALUE
+var MAGNITUDE_DIGITS = 3; // ditto
+var SEP = ''; // set to '_' for easier debugging 
+
+function collate(a, b) {
+
+  if (a === b) {
+    return 0;
+  }
+
+  a = normalizeKey(a);
+  b = normalizeKey(b);
+
+  var ai = collationIndex(a);
+  var bi = collationIndex(b);
+  if ((ai - bi) !== 0) {
+    return ai - bi;
+  }
+  switch (typeof a) {
+    case 'number':
+      return a - b;
+    case 'boolean':
+      return a < b ? -1 : 1;
+    case 'string':
+      return stringCollate(a, b);
+  }
+  return Array.isArray(a) ? arrayCollate(a, b) : objectCollate(a, b);
+}
+
+// couch considers null/NaN/Infinity/-Infinity === undefined,
+// for the purposes of mapreduce indexes. also, dates get stringified.
+function normalizeKey(key) {
+  switch (typeof key) {
+    case 'undefined':
+      return null;
+    case 'number':
+      if (key === Infinity || key === -Infinity || isNaN(key)) {
+        return null;
+      }
+      return key;
+    case 'object':
+      var origKey = key;
+      if (Array.isArray(key)) {
+        var len = key.length;
+        key = new Array(len);
+        for (var i = 0; i < len; i++) {
+          key[i] = normalizeKey(origKey[i]);
+        }
+      /* istanbul ignore next */
+      } else if (key instanceof Date) {
+        return key.toJSON();
+      } else if (key !== null) { // generic object
+        key = {};
+        for (var k in origKey) {
+          if (origKey.hasOwnProperty(k)) {
+            var val = origKey[k];
+            if (typeof val !== 'undefined') {
+              key[k] = normalizeKey(val);
+            }
+          }
+        }
+      }
+  }
+  return key;
+}
+
+function indexify(key) {
+  if (key !== null) {
+    switch (typeof key) {
+      case 'boolean':
+        return key ? 1 : 0;
+      case 'number':
+        return numToIndexableString(key);
+      case 'string':
+        // We've to be sure that key does not contain \u0000
+        // Do order-preserving replacements:
+        // 0 -> 1, 1
+        // 1 -> 1, 2
+        // 2 -> 2, 2
+        /* eslint-disable no-control-regex */
+        return key
+          .replace(/\u0002/g, '\u0002\u0002')
+          .replace(/\u0001/g, '\u0001\u0002')
+          .replace(/\u0000/g, '\u0001\u0001');
+        /* eslint-enable no-control-regex */
+      case 'object':
+        var isArray = Array.isArray(key);
+        var arr = isArray ? key : Object.keys(key);
+        var i = -1;
+        var len = arr.length;
+        var result = '';
+        if (isArray) {
+          while (++i < len) {
+            result += toIndexableString(arr[i]);
+          }
+        } else {
+          while (++i < len) {
+            var objKey = arr[i];
+            result += toIndexableString(objKey) +
+                toIndexableString(key[objKey]);
+          }
+        }
+        return result;
+    }
+  }
+  return '';
+}
+
+// convert the given key to a string that would be appropriate
+// for lexical sorting, e.g. within a database, where the
+// sorting is the same given by the collate() function.
+function toIndexableString(key) {
+  var zero = '\u0000';
+  key = normalizeKey(key);
+  return collationIndex(key) + SEP + indexify(key) + zero;
+}
+
+function parseNumber(str, i) {
+  var originalIdx = i;
+  var num;
+  var zero = str[i] === '1';
+  if (zero) {
+    num = 0;
+    i++;
+  } else {
+    var neg = str[i] === '0';
+    i++;
+    var numAsString = '';
+    var magAsString = str.substring(i, i + MAGNITUDE_DIGITS);
+    var magnitude = parseInt(magAsString, 10) + MIN_MAGNITUDE;
+    /* istanbul ignore next */
+    if (neg) {
+      magnitude = -magnitude;
+    }
+    i += MAGNITUDE_DIGITS;
+    while (true) {
+      var ch = str[i];
+      if (ch === '\u0000') {
+        break;
+      } else {
+        numAsString += ch;
+      }
+      i++;
+    }
+    numAsString = numAsString.split('.');
+    if (numAsString.length === 1) {
+      num = parseInt(numAsString, 10);
+    } else {
+      /* istanbul ignore next */
+      num = parseFloat(numAsString[0] + '.' + numAsString[1]);
+    }
+    /* istanbul ignore next */
+    if (neg) {
+      num = num - 10;
+    }
+    /* istanbul ignore next */
+    if (magnitude !== 0) {
+      // parseFloat is more reliable than pow due to rounding errors
+      // e.g. Number.MAX_VALUE would return Infinity if we did
+      // num * Math.pow(10, magnitude);
+      num = parseFloat(num + 'e' + magnitude);
+    }
+  }
+  return {num: num, length : i - originalIdx};
+}
+
+// move up the stack while parsing
+// this function moved outside of parseIndexableString for performance
+function pop(stack, metaStack) {
+  var obj = stack.pop();
+
+  if (metaStack.length) {
+    var lastMetaElement = metaStack[metaStack.length - 1];
+    if (obj === lastMetaElement.element) {
+      // popping a meta-element, e.g. an object whose value is another object
+      metaStack.pop();
+      lastMetaElement = metaStack[metaStack.length - 1];
+    }
+    var element = lastMetaElement.element;
+    var lastElementIndex = lastMetaElement.index;
+    if (Array.isArray(element)) {
+      element.push(obj);
+    } else if (lastElementIndex === stack.length - 2) { // obj with key+value
+      var key = stack.pop();
+      element[key] = obj;
+    } else {
+      stack.push(obj); // obj with key only
+    }
+  }
+}
+
+function parseIndexableString(str) {
+  var stack = [];
+  var metaStack = []; // stack for arrays and objects
+  var i = 0;
+
+  /*eslint no-constant-condition: ["error", { "checkLoops": false }]*/
+  while (true) {
+    var collationIndex = str[i++];
+    if (collationIndex === '\u0000') {
+      if (stack.length === 1) {
+        return stack.pop();
+      } else {
+        pop(stack, metaStack);
+        continue;
+      }
+    }
+    switch (collationIndex) {
+      case '1':
+        stack.push(null);
+        break;
+      case '2':
+        stack.push(str[i] === '1');
+        i++;
+        break;
+      case '3':
+        var parsedNum = parseNumber(str, i);
+        stack.push(parsedNum.num);
+        i += parsedNum.length;
+        break;
+      case '4':
+        var parsedStr = '';
+        /*eslint no-constant-condition: ["error", { "checkLoops": false }]*/
+        while (true) {
+          var ch = str[i];
+          if (ch === '\u0000') {
+            break;
+          }
+          parsedStr += ch;
+          i++;
+        }
+        // perform the reverse of the order-preserving replacement
+        // algorithm (see above)
+        /* eslint-disable no-control-regex */
+        parsedStr = parsedStr.replace(/\u0001\u0001/g, '\u0000')
+          .replace(/\u0001\u0002/g, '\u0001')
+          .replace(/\u0002\u0002/g, '\u0002');
+        /* eslint-enable no-control-regex */
+        stack.push(parsedStr);
+        break;
+      case '5':
+        var arrayElement = { element: [], index: stack.length };
+        stack.push(arrayElement.element);
+        metaStack.push(arrayElement);
+        break;
+      case '6':
+        var objElement = { element: {}, index: stack.length };
+        stack.push(objElement.element);
+        metaStack.push(objElement);
+        break;
+      /* istanbul ignore next */
+      default:
+        throw new Error(
+          'bad collationIndex or unexpectedly reached end of input: ' +
+            collationIndex);
+    }
+  }
+}
+
+function arrayCollate(a, b) {
+  var len = Math.min(a.length, b.length);
+  for (var i = 0; i < len; i++) {
+    var sort = collate(a[i], b[i]);
+    if (sort !== 0) {
+      return sort;
+    }
+  }
+  return (a.length === b.length) ? 0 :
+    (a.length > b.length) ? 1 : -1;
+}
+function stringCollate(a, b) {
+  // See: https://github.com/daleharvey/pouchdb/issues/40
+  // This is incompatible with the CouchDB implementation, but its the
+  // best we can do for now
+  return (a === b) ? 0 : ((a > b) ? 1 : -1);
+}
+function objectCollate(a, b) {
+  var ak = Object.keys(a), bk = Object.keys(b);
+  var len = Math.min(ak.length, bk.length);
+  for (var i = 0; i < len; i++) {
+    // First sort the keys
+    var sort = collate(ak[i], bk[i]);
+    if (sort !== 0) {
+      return sort;
+    }
+    // if the keys are equal sort the values
+    sort = collate(a[ak[i]], b[bk[i]]);
+    if (sort !== 0) {
+      return sort;
+    }
+
+  }
+  return (ak.length === bk.length) ? 0 :
+    (ak.length > bk.length) ? 1 : -1;
+}
+// The collation is defined by erlangs ordered terms
+// the atoms null, true, false come first, then numbers, strings,
+// arrays, then objects
+// null/undefined/NaN/Infinity/-Infinity are all considered null
+function collationIndex(x) {
+  var id = ['boolean', 'number', 'string', 'object'];
+  var idx = id.indexOf(typeof x);
+  //false if -1 otherwise true, but fast!!!!1
+  if (~idx) {
+    if (x === null) {
+      return 1;
+    }
+    if (Array.isArray(x)) {
+      return 5;
+    }
+    return idx < 3 ? (idx + 2) : (idx + 3);
+  }
+  /* istanbul ignore next */
+  if (Array.isArray(x)) {
+    return 5;
+  }
+}
+
+// conversion:
+// x yyy zz...zz
+// x = 0 for negative, 1 for 0, 2 for positive
+// y = exponent (for negative numbers negated) moved so that it's >= 0
+// z = mantisse
+function numToIndexableString(num) {
+
+  if (num === 0) {
+    return '1';
+  }
+
+  // convert number to exponential format for easier and
+  // more succinct string sorting
+  var expFormat = num.toExponential().split(/e\+?/);
+  var magnitude = parseInt(expFormat[1], 10);
+
+  var neg = num < 0;
+
+  var result = neg ? '0' : '2';
+
+  // first sort by magnitude
+  // it's easier if all magnitudes are positive
+  var magForComparison = ((neg ? -magnitude : magnitude) - MIN_MAGNITUDE);
+  var magString = padLeft((magForComparison).toString(), '0', MAGNITUDE_DIGITS);
+
+  result += SEP + magString;
+
+  // then sort by the factor
+  var factor = Math.abs(parseFloat(expFormat[0])); // [1..10)
+  /* istanbul ignore next */
+  if (neg) { // for negative reverse ordering
+    factor = 10 - factor;
+  }
+
+  var factorStr = factor.toFixed(20);
+
+  // strip zeros from the end
+  factorStr = factorStr.replace(/\.?0+$/, '');
+
+  result += SEP + factorStr;
+
+  return result;
+}
+
+// create a comparator based on the sort object
+function createFieldSorter(sort) {
+
+  function getFieldValuesAsArray(doc) {
+    return sort.map(function (sorting) {
+      var fieldName = getKey(sorting);
+      var parsedField = parseField(fieldName);
+      var docFieldValue = getFieldFromDoc(doc, parsedField);
+      return docFieldValue;
+    });
+  }
+
+  return function (aRow, bRow) {
+    var aFieldValues = getFieldValuesAsArray(aRow.doc);
+    var bFieldValues = getFieldValuesAsArray(bRow.doc);
+    var collation = collate(aFieldValues, bFieldValues);
+    if (collation !== 0) {
+      return collation;
+    }
+    // this is what mango seems to do
+    return compare$1(aRow.doc._id, bRow.doc._id);
+  };
+}
+
+function filterInMemoryFields(rows, requestDef, inMemoryFields) {
+  rows = rows.filter(function (row) {
+    return rowFilter(row.doc, requestDef.selector, inMemoryFields);
+  });
+
+  if (requestDef.sort) {
+    // in-memory sort
+    var fieldSorter = createFieldSorter(requestDef.sort);
+    rows = rows.sort(fieldSorter);
+    if (typeof requestDef.sort[0] !== 'string' &&
+        getValue(requestDef.sort[0]) === 'desc') {
+      rows = rows.reverse();
+    }
+  }
+
+  if ('limit' in requestDef || 'skip' in requestDef) {
+    // have to do the limit in-memory
+    var skip = requestDef.skip || 0;
+    var limit = ('limit' in requestDef ? requestDef.limit : rows.length) + skip;
+    rows = rows.slice(skip, limit);
+  }
+  return rows;
+}
+
+function rowFilter(doc, selector, inMemoryFields) {
+  return inMemoryFields.every(function (field) {
+    var matcher = selector[field];
+    var parsedField = parseField(field);
+    var docFieldValue = getFieldFromDoc(doc, parsedField);
+    if (isCombinationalField(field)) {
+      return matchCominationalSelector(field, matcher, doc);
+    }
+
+    return matchSelector(matcher, doc, parsedField, docFieldValue);
+  });
+}
+
+function matchSelector(matcher, doc, parsedField, docFieldValue) {
+  if (!matcher) {
+    // no filtering necessary; this field is just needed for sorting
+    return true;
+  }
+
+  // is matcher an object, if so continue recursion
+  if (typeof matcher === 'object') {
+    return Object.keys(matcher).every(function (userOperator) {
+      var userValue = matcher[userOperator];
+      return match(userOperator, doc, userValue, parsedField, docFieldValue);
+    });
+  }
+
+  // no more depth, No need to recurse further
+  return matcher === docFieldValue;
+}
+
+function matchCominationalSelector(field, matcher, doc) {
+
+  if (field === '$or') {
+    return matcher.some(function (orMatchers) {
+      return rowFilter(doc, orMatchers, Object.keys(orMatchers));
+    });
+  }
+
+  if (field === '$not') {
+    return !rowFilter(doc, matcher, Object.keys(matcher));
+  }
+
+  //`$nor`
+  return !matcher.find(function (orMatchers) {
+    return rowFilter(doc, orMatchers, Object.keys(orMatchers));
+  });
+
+}
+
+function match(userOperator, doc, userValue, parsedField, docFieldValue) {
+  if (!matchers[userOperator]) {
+    throw new Error('unknown operator "' + userOperator +
+      '" - should be one of $eq, $lte, $lt, $gt, $gte, $exists, $ne, $in, ' +
+      '$nin, $size, $mod, $regex, $elemMatch, $type, $allMatch or $all');
+  }
+  return matchers[userOperator](doc, userValue, parsedField, docFieldValue);
+}
+
+function fieldExists(docFieldValue) {
+  return typeof docFieldValue !== 'undefined' && docFieldValue !== null;
+}
+
+function fieldIsNotUndefined(docFieldValue) {
+  return typeof docFieldValue !== 'undefined';
+}
+
+function modField(docFieldValue, userValue) {
+  var divisor = userValue[0];
+  var mod = userValue[1];
+  if (divisor === 0) {
+    throw new Error('Bad divisor, cannot divide by zero');
+  }
+
+  if (parseInt(divisor, 10) !== divisor ) {
+    throw new Error('Divisor is not an integer');
+  }
+
+  if (parseInt(mod, 10) !== mod ) {
+    throw new Error('Modulus is not an integer');
+  }
+
+  if (parseInt(docFieldValue, 10) !== docFieldValue) {
+    return false;
+  }
+
+  return docFieldValue % divisor === mod;
+}
+
+function arrayContainsValue(docFieldValue, userValue) {
+  return userValue.some(function (val) {
+    if (docFieldValue instanceof Array) {
+      return docFieldValue.indexOf(val) > -1;
+    }
+
+    return docFieldValue === val;
+  });
+}
+
+function arrayContainsAllValues(docFieldValue, userValue) {
+  return userValue.every(function (val) {
+    return docFieldValue.indexOf(val) > -1;
+  });
+}
+
+function arraySize(docFieldValue, userValue) {
+  return docFieldValue.length === userValue;
+}
+
+function regexMatch(docFieldValue, userValue) {
+  var re = new RegExp(userValue);
+
+  return re.test(docFieldValue);
+}
+
+function typeMatch(docFieldValue, userValue) {
+
+  switch (userValue) {
+    case 'null':
+      return docFieldValue === null;
+    case 'boolean':
+      return typeof (docFieldValue) === 'boolean';
+    case 'number':
+      return typeof (docFieldValue) === 'number';
+    case 'string':
+      return typeof (docFieldValue) === 'string';
+    case 'array':
+      return docFieldValue instanceof Array;
+    case 'object':
+      return ({}).toString.call(docFieldValue) === '[object Object]';
+  }
+
+  throw new Error(userValue + ' not supported as a type.' +
+                  'Please use one of object, string, array, number, boolean or null.');
+
+}
+
+var matchers = {
+
+  '$elemMatch': function (doc, userValue, parsedField, docFieldValue) {
+    if (!Array.isArray(docFieldValue)) {
+      return false;
+    }
+
+    if (docFieldValue.length === 0) {
+      return false;
+    }
+
+    if (typeof docFieldValue[0] === 'object') {
+      return docFieldValue.some(function (val) {
+        return rowFilter(val, userValue, Object.keys(userValue));
+      });
+    }
+
+    return docFieldValue.some(function (val) {
+      return matchSelector(userValue, doc, parsedField, val);
+    });
+  },
+
+  '$allMatch': function (doc, userValue, parsedField, docFieldValue) {
+    if (!Array.isArray(docFieldValue)) {
+      return false;
+    }
+
+    /* istanbul ignore next */
+    if (docFieldValue.length === 0) {
+      return false;
+    }
+
+    if (typeof docFieldValue[0] === 'object') {
+      return docFieldValue.every(function (val) {
+        return rowFilter(val, userValue, Object.keys(userValue));
+      });
+    }
+
+    return docFieldValue.every(function (val) {
+      return matchSelector(userValue, doc, parsedField, val);
+    });
+  },
+
+  '$eq': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldIsNotUndefined(docFieldValue) && collate(docFieldValue, userValue) === 0;
+  },
+
+  '$gte': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldIsNotUndefined(docFieldValue) && collate(docFieldValue, userValue) >= 0;
+  },
+
+  '$gt': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldIsNotUndefined(docFieldValue) && collate(docFieldValue, userValue) > 0;
+  },
+
+  '$lte': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldIsNotUndefined(docFieldValue) && collate(docFieldValue, userValue) <= 0;
+  },
+
+  '$lt': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldIsNotUndefined(docFieldValue) && collate(docFieldValue, userValue) < 0;
+  },
+
+  '$exists': function (doc, userValue, parsedField, docFieldValue) {
+    //a field that is null is still considered to exist
+    if (userValue) {
+      return fieldIsNotUndefined(docFieldValue);
+    }
+
+    return !fieldIsNotUndefined(docFieldValue);
+  },
+
+  '$mod': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldExists(docFieldValue) && modField(docFieldValue, userValue);
+  },
+
+  '$ne': function (doc, userValue, parsedField, docFieldValue) {
+    return userValue.every(function (neValue) {
+      return collate(docFieldValue, neValue) !== 0;
+    });
+  },
+  '$in': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldExists(docFieldValue) && arrayContainsValue(docFieldValue, userValue);
+  },
+
+  '$nin': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldExists(docFieldValue) && !arrayContainsValue(docFieldValue, userValue);
+  },
+
+  '$size': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldExists(docFieldValue) && arraySize(docFieldValue, userValue);
+  },
+
+  '$all': function (doc, userValue, parsedField, docFieldValue) {
+    return Array.isArray(docFieldValue) && arrayContainsAllValues(docFieldValue, userValue);
+  },
+
+  '$regex': function (doc, userValue, parsedField, docFieldValue) {
+    return fieldExists(docFieldValue) && regexMatch(docFieldValue, userValue);
+  },
+
+  '$type': function (doc, userValue, parsedField, docFieldValue) {
+    return typeMatch(docFieldValue, userValue);
+  }
+};
+
+// return true if the given doc matches the supplied selector
+function matchesSelector(doc, selector) {
+  /* istanbul ignore if */
+  if (typeof selector !== 'object') {
+    // match the CouchDB error message
+    throw new Error('Selector error: expected a JSON object');
+  }
+
+  selector = massageSelector(selector);
+  var row = {
+    'doc': doc
+  };
+
+  var rowsMatched = filterInMemoryFields([row], { 'selector': selector }, Object.keys(selector));
+  return rowsMatched && rowsMatched.length === 1;
+}
+
+function evalFilter(input) {
+  return scopeEval('"use strict";\nreturn ' + input + ';', {});
+}
+
+function evalView(input) {
+  var code = [
+    'return function(doc) {',
+    '  "use strict";',
+    '  var emitted = false;',
+    '  var emit = function (a, b) {',
+    '    emitted = true;',
+    '  };',
+    '  var view = ' + input + ';',
+    '  view(doc);',
+    '  if (emitted) {',
+    '    return true;',
+    '  }',
+    '};'
+  ].join('\n');
+
+  return scopeEval(code, {});
+}
+
+function validate(opts, callback) {
+  if (opts.selector) {
+    if (opts.filter && opts.filter !== '_selector') {
+      var filterName = typeof opts.filter === 'string' ?
+        opts.filter : 'function';
+      return callback(new Error('selector invalid for filter "' + filterName + '"'));
+    }
+  }
+  callback();
+}
+
+function normalize(opts) {
+  if (opts.view && !opts.filter) {
+    opts.filter = '_view';
+  }
+
+  if (opts.selector && !opts.filter) {
+    opts.filter = '_selector';
+  }
+
+  if (opts.filter && typeof opts.filter === 'string') {
+    if (opts.filter === '_view') {
+      opts.view = normalizeDesignDocFunctionName(opts.view);
+    } else {
+      opts.filter = normalizeDesignDocFunctionName(opts.filter);
+    }
+  }
+}
+
+function shouldFilter(changesHandler, opts) {
+  return opts.filter && typeof opts.filter === 'string' &&
+    !opts.doc_ids && !isRemote(changesHandler.db);
+}
+
+function filter(changesHandler, opts) {
+  var callback = opts.complete;
+  if (opts.filter === '_view') {
+    if (!opts.view || typeof opts.view !== 'string') {
+      var err = createError(BAD_REQUEST,
+        '`view` filter parameter not found or invalid.');
+      return callback(err);
+    }
+    // fetch a view from a design doc, make it behave like a filter
+    var viewName = parseDesignDocFunctionName(opts.view);
+    changesHandler.db.get('_design/' + viewName[0], function (err, ddoc) {
+      /* istanbul ignore if */
+      if (changesHandler.isCancelled) {
+        return callback(null, {status: 'cancelled'});
+      }
+      /* istanbul ignore next */
+      if (err) {
+        return callback(generateErrorFromResponse(err));
+      }
+      var mapFun = ddoc && ddoc.views && ddoc.views[viewName[1]] &&
+        ddoc.views[viewName[1]].map;
+      if (!mapFun) {
+        return callback(createError(MISSING_DOC,
+          (ddoc.views ? 'missing json key: ' + viewName[1] :
+            'missing json key: views')));
+      }
+      opts.filter = evalView(mapFun);
+      changesHandler.doChanges(opts);
+    });
+  } else if (opts.selector) {
+    opts.filter = function (doc) {
+      return matchesSelector(doc, opts.selector);
+    };
+    changesHandler.doChanges(opts);
+  } else {
+    // fetch a filter from a design doc
+    var filterName = parseDesignDocFunctionName(opts.filter);
+    changesHandler.db.get('_design/' + filterName[0], function (err, ddoc) {
+      /* istanbul ignore if */
+      if (changesHandler.isCancelled) {
+        return callback(null, {status: 'cancelled'});
+      }
+      /* istanbul ignore next */
+      if (err) {
+        return callback(generateErrorFromResponse(err));
+      }
+      var filterFun = ddoc && ddoc.filters && ddoc.filters[filterName[1]];
+      if (!filterFun) {
+        return callback(createError(MISSING_DOC,
+          ((ddoc && ddoc.filters) ? 'missing json key: ' + filterName[1]
+            : 'missing json key: filters')));
+      }
+      opts.filter = evalFilter(filterFun);
+      changesHandler.doChanges(opts);
+    });
+  }
+}
+
+function applyChangesFilterPlugin(PouchDB) {
+  PouchDB._changesFilterPlugin = {
+    validate: validate,
+    normalize: normalize,
+    shouldFilter: shouldFilter,
+    filter: filter
+  };
+}
+
+// TODO: remove from pouchdb-core (breaking)
+PouchDB.plugin(applyChangesFilterPlugin);
+
+PouchDB.version = version;
+
+function toObject(array) {
+  return array.reduce(function (obj, item) {
+    obj[item] = true;
+    return obj;
+  }, {});
+}
+// List of top level reserved words for doc
+var reservedWords = toObject([
+  '_id',
+  '_rev',
+  '_attachments',
+  '_deleted',
+  '_revisions',
+  '_revs_info',
+  '_conflicts',
+  '_deleted_conflicts',
+  '_local_seq',
+  '_rev_tree',
+  //replication documents
+  '_replication_id',
+  '_replication_state',
+  '_replication_state_time',
+  '_replication_state_reason',
+  '_replication_stats',
+  // Specific to Couchbase Sync Gateway
+  '_removed'
+]);
+
+// List of reserved words that should end up the document
+var dataWords = toObject([
+  '_attachments',
+  //replication documents
+  '_replication_id',
+  '_replication_state',
+  '_replication_state_time',
+  '_replication_state_reason',
+  '_replication_stats'
+]);
+
+function parseRevisionInfo(rev$$1) {
+  if (!/^\d+-./.test(rev$$1)) {
+    return createError(INVALID_REV);
+  }
+  var idx = rev$$1.indexOf('-');
+  var left = rev$$1.substring(0, idx);
+  var right = rev$$1.substring(idx + 1);
+  return {
+    prefix: parseInt(left, 10),
+    id: right
+  };
+}
+
+function makeRevTreeFromRevisions(revisions, opts) {
+  var pos = revisions.start - revisions.ids.length + 1;
+
+  var revisionIds = revisions.ids;
+  var ids = [revisionIds[0], opts, []];
+
+  for (var i = 1, len = revisionIds.length; i < len; i++) {
+    ids = [revisionIds[i], {status: 'missing'}, [ids]];
+  }
+
+  return [{
+    pos: pos,
+    ids: ids
+  }];
+}
+
+// Preprocess documents, parse their revisions, assign an id and a
+// revision for new writes that are missing them, etc
+function parseDoc(doc, newEdits, dbOpts) {
+  if (!dbOpts) {
+    dbOpts = {
+      deterministic_revs: true
+    };
+  }
+
+  var nRevNum;
+  var newRevId;
+  var revInfo;
+  var opts = {status: 'available'};
+  if (doc._deleted) {
+    opts.deleted = true;
+  }
+
+  if (newEdits) {
+    if (!doc._id) {
+      doc._id = uuid();
+    }
+    newRevId = rev(doc, dbOpts.deterministic_revs);
+    if (doc._rev) {
+      revInfo = parseRevisionInfo(doc._rev);
+      if (revInfo.error) {
+        return revInfo;
+      }
+      doc._rev_tree = [{
+        pos: revInfo.prefix,
+        ids: [revInfo.id, {status: 'missing'}, [[newRevId, opts, []]]]
+      }];
+      nRevNum = revInfo.prefix + 1;
+    } else {
+      doc._rev_tree = [{
+        pos: 1,
+        ids : [newRevId, opts, []]
+      }];
+      nRevNum = 1;
+    }
+  } else {
+    if (doc._revisions) {
+      doc._rev_tree = makeRevTreeFromRevisions(doc._revisions, opts);
+      nRevNum = doc._revisions.start;
+      newRevId = doc._revisions.ids[0];
+    }
+    if (!doc._rev_tree) {
+      revInfo = parseRevisionInfo(doc._rev);
+      if (revInfo.error) {
+        return revInfo;
+      }
+      nRevNum = revInfo.prefix;
+      newRevId = revInfo.id;
+      doc._rev_tree = [{
+        pos: nRevNum,
+        ids: [newRevId, opts, []]
+      }];
+    }
+  }
+
+  invalidIdError(doc._id);
+
+  doc._rev = nRevNum + '-' + newRevId;
+
+  var result = {metadata : {}, data : {}};
+  for (var key in doc) {
+    /* istanbul ignore else */
+    if (Object.prototype.hasOwnProperty.call(doc, key)) {
+      var specialKey = key[0] === '_';
+      if (specialKey && !reservedWords[key]) {
+        var error = createError(DOC_VALIDATION, key);
+        error.message = DOC_VALIDATION.message + ': ' + key;
+        throw error;
+      } else if (specialKey && !dataWords[key]) {
+        result.metadata[key.slice(1)] = doc[key];
+      } else {
+        result.data[key] = doc[key];
+      }
+    }
+  }
+  return result;
+}
+
+function parseBase64(data) {
+  try {
+    return thisAtob(data);
+  } catch (e) {
+    var err = createError(BAD_ARG,
+      'Attachment is not a valid base64 string');
+    return {error: err};
+  }
+}
+
+function preprocessString(att, blobType, callback) {
+  var asBinary = parseBase64(att.data);
+  if (asBinary.error) {
+    return callback(asBinary.error);
+  }
+
+  att.length = asBinary.length;
+  if (blobType === 'blob') {
+    att.data = binStringToBluffer(asBinary, att.content_type);
+  } else if (blobType === 'base64') {
+    att.data = thisBtoa(asBinary);
+  } else { // binary
+    att.data = asBinary;
+  }
+  binaryMd5(asBinary, function (result) {
+    att.digest = 'md5-' + result;
+    callback();
+  });
+}
+
+function preprocessBlob(att, blobType, callback) {
+  binaryMd5(att.data, function (md5) {
+    att.digest = 'md5-' + md5;
+    // size is for blobs (browser), length is for buffers (node)
+    att.length = att.data.size || att.data.length || 0;
+    if (blobType === 'binary') {
+      blobToBinaryString(att.data, function (binString) {
+        att.data = binString;
+        callback();
+      });
+    } else if (blobType === 'base64') {
+      blobToBase64(att.data, function (b64) {
+        att.data = b64;
+        callback();
+      });
+    } else {
+      callback();
+    }
+  });
+}
+
+function preprocessAttachment(att, blobType, callback) {
+  if (att.stub) {
+    return callback();
+  }
+  if (typeof att.data === 'string') { // input is a base64 string
+    preprocessString(att, blobType, callback);
+  } else { // input is a blob
+    preprocessBlob(att, blobType, callback);
+  }
+}
+
+function preprocessAttachments(docInfos, blobType, callback) {
+
+  if (!docInfos.length) {
+    return callback();
+  }
+
+  var docv = 0;
+  var overallErr;
+
+  docInfos.forEach(function (docInfo) {
+    var attachments = docInfo.data && docInfo.data._attachments ?
+      Object.keys(docInfo.data._attachments) : [];
+    var recv = 0;
+
+    if (!attachments.length) {
+      return done();
+    }
+
+    function processedAttachment(err) {
+      overallErr = err;
+      recv++;
+      if (recv === attachments.length) {
+        done();
+      }
+    }
+
+    for (var key in docInfo.data._attachments) {
+      if (docInfo.data._attachments.hasOwnProperty(key)) {
+        preprocessAttachment(docInfo.data._attachments[key],
+          blobType, processedAttachment);
+      }
+    }
+  });
+
+  function done() {
+    docv++;
+    if (docInfos.length === docv) {
+      if (overallErr) {
+        callback(overallErr);
+      } else {
+        callback();
+      }
+    }
+  }
+}
+
+function updateDoc(revLimit, prev, docInfo, results,
+                   i, cb, writeDoc, newEdits) {
+
+  if (revExists(prev.rev_tree, docInfo.metadata.rev) && !newEdits) {
+    results[i] = docInfo;
+    return cb();
+  }
+
+  // sometimes this is pre-calculated. historically not always
+  var previousWinningRev = prev.winningRev || winningRev(prev);
+  var previouslyDeleted = 'deleted' in prev ? prev.deleted :
+    isDeleted(prev, previousWinningRev);
+  var deleted = 'deleted' in docInfo.metadata ? docInfo.metadata.deleted :
+    isDeleted(docInfo.metadata);
+  var isRoot = /^1-/.test(docInfo.metadata.rev);
+
+  if (previouslyDeleted && !deleted && newEdits && isRoot) {
+    var newDoc = docInfo.data;
+    newDoc._rev = previousWinningRev;
+    newDoc._id = docInfo.metadata.id;
+    docInfo = parseDoc(newDoc, newEdits);
+  }
+
+  var merged = merge(prev.rev_tree, docInfo.metadata.rev_tree[0], revLimit);
+
+  var inConflict = newEdits && ((
+    (previouslyDeleted && deleted && merged.conflicts !== 'new_leaf') ||
+    (!previouslyDeleted && merged.conflicts !== 'new_leaf') ||
+    (previouslyDeleted && !deleted && merged.conflicts === 'new_branch')));
+
+  if (inConflict) {
+    var err = createError(REV_CONFLICT);
+    results[i] = err;
+    return cb();
+  }
+
+  var newRev = docInfo.metadata.rev;
+  docInfo.metadata.rev_tree = merged.tree;
+  docInfo.stemmedRevs = merged.stemmedRevs || [];
+  /* istanbul ignore else */
+  if (prev.rev_map) {
+    docInfo.metadata.rev_map = prev.rev_map; // used only by leveldb
+  }
+
+  // recalculate
+  var winningRev$$1 = winningRev(docInfo.metadata);
+  var winningRevIsDeleted = isDeleted(docInfo.metadata, winningRev$$1);
+
+  // calculate the total number of documents that were added/removed,
+  // from the perspective of total_rows/doc_count
+  var delta = (previouslyDeleted === winningRevIsDeleted) ? 0 :
+    previouslyDeleted < winningRevIsDeleted ? -1 : 1;
+
+  var newRevIsDeleted;
+  if (newRev === winningRev$$1) {
+    // if the new rev is the same as the winning rev, we can reuse that value
+    newRevIsDeleted = winningRevIsDeleted;
+  } else {
+    // if they're not the same, then we need to recalculate
+    newRevIsDeleted = isDeleted(docInfo.metadata, newRev);
+  }
+
+  writeDoc(docInfo, winningRev$$1, winningRevIsDeleted, newRevIsDeleted,
+    true, delta, i, cb);
+}
+
+function rootIsMissing(docInfo) {
+  return docInfo.metadata.rev_tree[0].ids[1].status === 'missing';
+}
+
+function processDocs(revLimit, docInfos, api, fetchedDocs, tx, results,
+                     writeDoc, opts, overallCallback) {
+
+  // Default to 1000 locally
+  revLimit = revLimit || 1000;
+
+  function insertDoc(docInfo, resultsIdx, callback) {
+    // Cant insert new deleted documents
+    var winningRev$$1 = winningRev(docInfo.metadata);
+    var deleted = isDeleted(docInfo.metadata, winningRev$$1);
+    if ('was_delete' in opts && deleted) {
+      results[resultsIdx] = createError(MISSING_DOC, 'deleted');
+      return callback();
+    }
+
+    // 4712 - detect whether a new document was inserted with a _rev
+    var inConflict = newEdits && rootIsMissing(docInfo);
+
+    if (inConflict) {
+      var err = createError(REV_CONFLICT);
+      results[resultsIdx] = err;
+      return callback();
+    }
+
+    var delta = deleted ? 0 : 1;
+
+    writeDoc(docInfo, winningRev$$1, deleted, deleted, false,
+      delta, resultsIdx, callback);
+  }
+
+  var newEdits = opts.new_edits;
+  var idsToDocs = new ExportedMap();
+
+  var docsDone = 0;
+  var docsToDo = docInfos.length;
+
+  function checkAllDocsDone() {
+    if (++docsDone === docsToDo && overallCallback) {
+      overallCallback();
+    }
+  }
+
+  docInfos.forEach(function (currentDoc, resultsIdx) {
+
+    if (currentDoc._id && isLocalId(currentDoc._id)) {
+      var fun = currentDoc._deleted ? '_removeLocal' : '_putLocal';
+      api[fun](currentDoc, {ctx: tx}, function (err, res) {
+        results[resultsIdx] = err || res;
+        checkAllDocsDone();
+      });
+      return;
+    }
+
+    var id = currentDoc.metadata.id;
+    if (idsToDocs.has(id)) {
+      docsToDo--; // duplicate
+      idsToDocs.get(id).push([currentDoc, resultsIdx]);
+    } else {
+      idsToDocs.set(id, [[currentDoc, resultsIdx]]);
+    }
+  });
+
+  // in the case of new_edits, the user can provide multiple docs
+  // with the same id. these need to be processed sequentially
+  idsToDocs.forEach(function (docs, id) {
+    var numDone = 0;
+
+    function docWritten() {
+      if (++numDone < docs.length) {
+        nextDoc();
+      } else {
+        checkAllDocsDone();
+      }
+    }
+    function nextDoc() {
+      var value = docs[numDone];
+      var currentDoc = value[0];
+      var resultsIdx = value[1];
+
+      if (fetchedDocs.has(id)) {
+        updateDoc(revLimit, fetchedDocs.get(id), currentDoc, results,
+          resultsIdx, docWritten, writeDoc, newEdits);
+      } else {
+        // Ensure stemming applies to new writes as well
+        var merged = merge([], currentDoc.metadata.rev_tree[0], revLimit);
+        currentDoc.metadata.rev_tree = merged.tree;
+        currentDoc.stemmedRevs = merged.stemmedRevs || [];
+        insertDoc(currentDoc, resultsIdx, docWritten);
+      }
+    }
+    nextDoc();
+  });
+}
+
+// IndexedDB requires a versioned database structure, so we use the
+// version here to manage migrations.
+var ADAPTER_VERSION = 5;
+
+// The object stores created for each database
+// DOC_STORE stores the document meta data, its revision history and state
+// Keyed by document id
+var DOC_STORE = 'document-store';
+// BY_SEQ_STORE stores a particular version of a document, keyed by its
+// sequence id
+var BY_SEQ_STORE = 'by-sequence';
+// Where we store attachments
+var ATTACH_STORE = 'attach-store';
+// Where we store many-to-many relations
+// between attachment digests and seqs
+var ATTACH_AND_SEQ_STORE = 'attach-seq-store';
+
+// Where we store database-wide meta data in a single record
+// keyed by id: META_STORE
+var META_STORE = 'meta-store';
+// Where we store local documents
+var LOCAL_STORE = 'local-store';
+// Where we detect blob support
+var DETECT_BLOB_SUPPORT_STORE = 'detect-blob-support';
+
+function safeJsonParse(str) {
+  // This try/catch guards against stack overflow errors.
+  // JSON.parse() is faster than vuvuzela.parse() but vuvuzela
+  // cannot overflow.
+  try {
+    return JSON.parse(str);
+  } catch (e) {
+    /* istanbul ignore next */
+    return vuvuzela.parse(str);
+  }
+}
+
+function safeJsonStringify(json) {
+  try {
+    return JSON.stringify(json);
+  } catch (e) {
+    /* istanbul ignore next */
+    return vuvuzela.stringify(json);
+  }
+}
+
+function idbError(callback) {
+  return function (evt) {
+    var message = 'unknown_error';
+    if (evt.target && evt.target.error) {
+      message = evt.target.error.name || evt.target.error.message;
+    }
+    callback(createError(IDB_ERROR, message, evt.type));
+  };
+}
+
+// Unfortunately, the metadata has to be stringified
+// when it is put into the database, because otherwise
+// IndexedDB can throw errors for deeply-nested objects.
+// Originally we just used JSON.parse/JSON.stringify; now
+// we use this custom vuvuzela library that avoids recursion.
+// If we could do it all over again, we'd probably use a
+// format for the revision trees other than JSON.
+function encodeMetadata(metadata, winningRev, deleted) {
+  return {
+    data: safeJsonStringify(metadata),
+    winningRev: winningRev,
+    deletedOrLocal: deleted ? '1' : '0',
+    seq: metadata.seq, // highest seq for this doc
+    id: metadata.id
+  };
+}
+
+function decodeMetadata(storedObject) {
+  if (!storedObject) {
+    return null;
+  }
+  var metadata = safeJsonParse(storedObject.data);
+  metadata.winningRev = storedObject.winningRev;
+  metadata.deleted = storedObject.deletedOrLocal === '1';
+  metadata.seq = storedObject.seq;
+  return metadata;
+}
+
+// read the doc back out from the database. we don't store the
+// _id or _rev because we already have _doc_id_rev.
+function decodeDoc(doc) {
+  if (!doc) {
+    return doc;
+  }
+  var idx = doc._doc_id_rev.lastIndexOf(':');
+  doc._id = doc._doc_id_rev.substring(0, idx - 1);
+  doc._rev = doc._doc_id_rev.substring(idx + 1);
+  delete doc._doc_id_rev;
+  return doc;
+}
+
+// Read a blob from the database, encoding as necessary
+// and translating from base64 if the IDB doesn't support
+// native Blobs
+function readBlobData(body, type, asBlob, callback) {
+  if (asBlob) {
+    if (!body) {
+      callback(createBlob([''], {type: type}));
+    } else if (typeof body !== 'string') { // we have blob support
+      callback(body);
+    } else { // no blob support
+      callback(b64ToBluffer(body, type));
+    }
+  } else { // as base64 string
+    if (!body) {
+      callback('');
+    } else if (typeof body !== 'string') { // we have blob support
+      readAsBinaryString(body, function (binary) {
+        callback(thisBtoa(binary));
+      });
+    } else { // no blob support
+      callback(body);
+    }
+  }
+}
+
+function fetchAttachmentsIfNecessary(doc, opts, txn, cb) {
+  var attachments = Object.keys(doc._attachments || {});
+  if (!attachments.length) {
+    return cb && cb();
+  }
+  var numDone = 0;
+
+  function checkDone() {
+    if (++numDone === attachments.length && cb) {
+      cb();
+    }
+  }
+
+  function fetchAttachment(doc, att) {
+    var attObj = doc._attachments[att];
+    var digest = attObj.digest;
+    var req = txn.objectStore(ATTACH_STORE).get(digest);
+    req.onsuccess = function (e) {
+      attObj.body = e.target.result.body;
+      checkDone();
+    };
+  }
+
+  attachments.forEach(function (att) {
+    if (opts.attachments && opts.include_docs) {
+      fetchAttachment(doc, att);
+    } else {
+      doc._attachments[att].stub = true;
+      checkDone();
+    }
+  });
+}
+
+// IDB-specific postprocessing necessary because
+// we don't know whether we stored a true Blob or
+// a base64-encoded string, and if it's a Blob it
+// needs to be read outside of the transaction context
+function postProcessAttachments(results, asBlob) {
+  return Promise.all(results.map(function (row) {
+    if (row.doc && row.doc._attachments) {
+      var attNames = Object.keys(row.doc._attachments);
+      return Promise.all(attNames.map(function (att) {
+        var attObj = row.doc._attachments[att];
+        if (!('body' in attObj)) { // already processed
+          return;
+        }
+        var body = attObj.body;
+        var type = attObj.content_type;
+        return new Promise(function (resolve) {
+          readBlobData(body, type, asBlob, function (data) {
+            row.doc._attachments[att] = $inject_Object_assign(
+              pick(attObj, ['digest', 'content_type']),
+              {data: data}
+            );
+            resolve();
+          });
+        });
+      }));
+    }
+  }));
+}
+
+function compactRevs(revs, docId, txn) {
+
+  var possiblyOrphanedDigests = [];
+  var seqStore = txn.objectStore(BY_SEQ_STORE);
+  var attStore = txn.objectStore(ATTACH_STORE);
+  var attAndSeqStore = txn.objectStore(ATTACH_AND_SEQ_STORE);
+  var count = revs.length;
+
+  function checkDone() {
+    count--;
+    if (!count) { // done processing all revs
+      deleteOrphanedAttachments();
+    }
+  }
+
+  function deleteOrphanedAttachments() {
+    if (!possiblyOrphanedDigests.length) {
+      return;
+    }
+    possiblyOrphanedDigests.forEach(function (digest) {
+      var countReq = attAndSeqStore.index('digestSeq').count(
+        IDBKeyRange.bound(
+          digest + '::', digest + '::\uffff', false, false));
+      countReq.onsuccess = function (e) {
+        var count = e.target.result;
+        if (!count) {
+          // orphaned
+          attStore["delete"](digest);
+        }
+      };
+    });
+  }
+
+  revs.forEach(function (rev$$1) {
+    var index = seqStore.index('_doc_id_rev');
+    var key = docId + "::" + rev$$1;
+    index.getKey(key).onsuccess = function (e) {
+      var seq = e.target.result;
+      if (typeof seq !== 'number') {
+        return checkDone();
+      }
+      seqStore["delete"](seq);
+
+      var cursor = attAndSeqStore.index('seq')
+        .openCursor(IDBKeyRange.only(seq));
+
+      cursor.onsuccess = function (event) {
+        var cursor = event.target.result;
+        if (cursor) {
+          var digest = cursor.value.digestSeq.split('::')[0];
+          possiblyOrphanedDigests.push(digest);
+          attAndSeqStore["delete"](cursor.primaryKey);
+          cursor["continue"]();
+        } else { // done
+          checkDone();
+        }
+      };
+    };
+  });
+}
+
+function openTransactionSafely(idb, stores, mode) {
+  try {
+    return {
+      txn: idb.transaction(stores, mode)
+    };
+  } catch (err) {
+    return {
+      error: err
+    };
+  }
+}
+
+var changesHandler = new Changes();
+
+function idbBulkDocs(dbOpts, req, opts, api, idb, callback) {
+  var docInfos = req.docs;
+  var txn;
+  var docStore;
+  var bySeqStore;
+  var attachStore;
+  var attachAndSeqStore;
+  var metaStore;
+  var docInfoError;
+  var metaDoc;
+
+  for (var i = 0, len = docInfos.length; i < len; i++) {
+    var doc = docInfos[i];
+    if (doc._id && isLocalId(doc._id)) {
+      continue;
+    }
+    doc = docInfos[i] = parseDoc(doc, opts.new_edits, dbOpts);
+    if (doc.error && !docInfoError) {
+      docInfoError = doc;
+    }
+  }
+
+  if (docInfoError) {
+    return callback(docInfoError);
+  }
+
+  var allDocsProcessed = false;
+  var docCountDelta = 0;
+  var results = new Array(docInfos.length);
+  var fetchedDocs = new ExportedMap();
+  var preconditionErrored = false;
+  var blobType = api._meta.blobSupport ? 'blob' : 'base64';
+
+  preprocessAttachments(docInfos, blobType, function (err) {
+    if (err) {
+      return callback(err);
+    }
+    startTransaction();
+  });
+
+  function startTransaction() {
+
+    var stores = [
+      DOC_STORE, BY_SEQ_STORE,
+      ATTACH_STORE,
+      LOCAL_STORE, ATTACH_AND_SEQ_STORE,
+      META_STORE
+    ];
+    var txnResult = openTransactionSafely(idb, stores, 'readwrite');
+    if (txnResult.error) {
+      return callback(txnResult.error);
+    }
+    txn = txnResult.txn;
+    txn.onabort = idbError(callback);
+    txn.ontimeout = idbError(callback);
+    txn.oncomplete = complete;
+    docStore = txn.objectStore(DOC_STORE);
+    bySeqStore = txn.objectStore(BY_SEQ_STORE);
+    attachStore = txn.objectStore(ATTACH_STORE);
+    attachAndSeqStore = txn.objectStore(ATTACH_AND_SEQ_STORE);
+    metaStore = txn.objectStore(META_STORE);
+
+    metaStore.get(META_STORE).onsuccess = function (e) {
+      metaDoc = e.target.result;
+      updateDocCountIfReady();
+    };
+
+    verifyAttachments(function (err) {
+      if (err) {
+        preconditionErrored = true;
+        return callback(err);
+      }
+      fetchExistingDocs();
+    });
+  }
+
+  function onAllDocsProcessed() {
+    allDocsProcessed = true;
+    updateDocCountIfReady();
+  }
+
+  function idbProcessDocs() {
+    processDocs(dbOpts.revs_limit, docInfos, api, fetchedDocs,
+                txn, results, writeDoc, opts, onAllDocsProcessed);
+  }
+
+  function updateDocCountIfReady() {
+    if (!metaDoc || !allDocsProcessed) {
+      return;
+    }
+    // caching the docCount saves a lot of time in allDocs() and
+    // info(), which is why we go to all the trouble of doing this
+    metaDoc.docCount += docCountDelta;
+    metaStore.put(metaDoc);
+  }
+
+  function fetchExistingDocs() {
+
+    if (!docInfos.length) {
+      return;
+    }
+
+    var numFetched = 0;
+
+    function checkDone() {
+      if (++numFetched === docInfos.length) {
+        idbProcessDocs();
+      }
+    }
+
+    function readMetadata(event) {
+      var metadata = decodeMetadata(event.target.result);
+
+      if (metadata) {
+        fetchedDocs.set(metadata.id, metadata);
+      }
+      checkDone();
+    }
+
+    for (var i = 0, len = docInfos.length; i < len; i++) {
+      var docInfo = docInfos[i];
+      if (docInfo._id && isLocalId(docInfo._id)) {
+        checkDone(); // skip local docs
+        continue;
+      }
+      var req = docStore.get(docInfo.metadata.id);
+      req.onsuccess = readMetadata;
+    }
+  }
+
+  function complete() {
+    if (preconditionErrored) {
+      return;
+    }
+
+    changesHandler.notify(api._meta.name);
+    callback(null, results);
+  }
+
+  function verifyAttachment(digest, callback) {
+
+    var req = attachStore.get(digest);
+    req.onsuccess = function (e) {
+      if (!e.target.result) {
+        var err = createError(MISSING_STUB,
+          'unknown stub attachment with digest ' +
+          digest);
+        err.status = 412;
+        callback(err);
+      } else {
+        callback();
+      }
+    };
+  }
+
+  function verifyAttachments(finish) {
+
+
+    var digests = [];
+    docInfos.forEach(function (docInfo) {
+      if (docInfo.data && docInfo.data._attachments) {
+        Object.keys(docInfo.data._attachments).forEach(function (filename) {
+          var att = docInfo.data._attachments[filename];
+          if (att.stub) {
+            digests.push(att.digest);
+          }
+        });
+      }
+    });
+    if (!digests.length) {
+      return finish();
+    }
+    var numDone = 0;
+    var err;
+
+    function checkDone() {
+      if (++numDone === digests.length) {
+        finish(err);
+      }
+    }
+    digests.forEach(function (digest) {
+      verifyAttachment(digest, function (attErr) {
+        if (attErr && !err) {
+          err = attErr;
+        }
+        checkDone();
+      });
+    });
+  }
+
+  function writeDoc(docInfo, winningRev$$1, winningRevIsDeleted, newRevIsDeleted,
+                    isUpdate, delta, resultsIdx, callback) {
+
+    docInfo.metadata.winningRev = winningRev$$1;
+    docInfo.metadata.deleted = winningRevIsDeleted;
+
+    var doc = docInfo.data;
+    doc._id = docInfo.metadata.id;
+    doc._rev = docInfo.metadata.rev;
+
+    if (newRevIsDeleted) {
+      doc._deleted = true;
+    }
+
+    var hasAttachments = doc._attachments &&
+      Object.keys(doc._attachments).length;
+    if (hasAttachments) {
+      return writeAttachments(docInfo, winningRev$$1, winningRevIsDeleted,
+        isUpdate, resultsIdx, callback);
+    }
+
+    docCountDelta += delta;
+    updateDocCountIfReady();
+
+    finishDoc(docInfo, winningRev$$1, winningRevIsDeleted,
+      isUpdate, resultsIdx, callback);
+  }
+
+  function finishDoc(docInfo, winningRev$$1, winningRevIsDeleted,
+                     isUpdate, resultsIdx, callback) {
+
+    var doc = docInfo.data;
+    var metadata = docInfo.metadata;
+
+    doc._doc_id_rev = metadata.id + '::' + metadata.rev;
+    delete doc._id;
+    delete doc._rev;
+
+    function afterPutDoc(e) {
+      var revsToDelete = docInfo.stemmedRevs || [];
+
+      if (isUpdate && api.auto_compaction) {
+        revsToDelete = revsToDelete.concat(compactTree(docInfo.metadata));
+      }
+
+      if (revsToDelete && revsToDelete.length) {
+        compactRevs(revsToDelete, docInfo.metadata.id, txn);
+      }
+
+      metadata.seq = e.target.result;
+      // Current _rev is calculated from _rev_tree on read
+      // delete metadata.rev;
+      var metadataToStore = encodeMetadata(metadata, winningRev$$1,
+        winningRevIsDeleted);
+      var metaDataReq = docStore.put(metadataToStore);
+      metaDataReq.onsuccess = afterPutMetadata;
+    }
+
+    function afterPutDocError(e) {
+      // ConstraintError, need to update, not put (see #1638 for details)
+      e.preventDefault(); // avoid transaction abort
+      e.stopPropagation(); // avoid transaction onerror
+      var index = bySeqStore.index('_doc_id_rev');
+      var getKeyReq = index.getKey(doc._doc_id_rev);
+      getKeyReq.onsuccess = function (e) {
+        var putReq = bySeqStore.put(doc, e.target.result);
+        putReq.onsuccess = afterPutDoc;
+      };
+    }
+
+    function afterPutMetadata() {
+      results[resultsIdx] = {
+        ok: true,
+        id: metadata.id,
+        rev: metadata.rev
+      };
+      fetchedDocs.set(docInfo.metadata.id, docInfo.metadata);
+      insertAttachmentMappings(docInfo, metadata.seq, callback);
+    }
+
+    var putReq = bySeqStore.put(doc);
+
+    putReq.onsuccess = afterPutDoc;
+    putReq.onerror = afterPutDocError;
+  }
+
+  function writeAttachments(docInfo, winningRev$$1, winningRevIsDeleted,
+                            isUpdate, resultsIdx, callback) {
+
+
+    var doc = docInfo.data;
+
+    var numDone = 0;
+    var attachments = Object.keys(doc._attachments);
+
+    function collectResults() {
+      if (numDone === attachments.length) {
+        finishDoc(docInfo, winningRev$$1, winningRevIsDeleted,
+          isUpdate, resultsIdx, callback);
+      }
+    }
+
+    function attachmentSaved() {
+      numDone++;
+      collectResults();
+    }
+
+    attachments.forEach(function (key) {
+      var att = docInfo.data._attachments[key];
+      if (!att.stub) {
+        var data = att.data;
+        delete att.data;
+        att.revpos = parseInt(winningRev$$1, 10);
+        var digest = att.digest;
+        saveAttachment(digest, data, attachmentSaved);
+      } else {
+        numDone++;
+        collectResults();
+      }
+    });
+  }
+
+  // map seqs to attachment digests, which
+  // we will need later during compaction
+  function insertAttachmentMappings(docInfo, seq, callback) {
+
+    var attsAdded = 0;
+    var attsToAdd = Object.keys(docInfo.data._attachments || {});
+
+    if (!attsToAdd.length) {
+      return callback();
+    }
+
+    function checkDone() {
+      if (++attsAdded === attsToAdd.length) {
+        callback();
+      }
+    }
+
+    function add(att) {
+      var digest = docInfo.data._attachments[att].digest;
+      var req = attachAndSeqStore.put({
+        seq: seq,
+        digestSeq: digest + '::' + seq
+      });
+
+      req.onsuccess = checkDone;
+      req.onerror = function (e) {
+        // this callback is for a constaint error, which we ignore
+        // because this docid/rev has already been associated with
+        // the digest (e.g. when new_edits == false)
+        e.preventDefault(); // avoid transaction abort
+        e.stopPropagation(); // avoid transaction onerror
+        checkDone();
+      };
+    }
+    for (var i = 0; i < attsToAdd.length; i++) {
+      add(attsToAdd[i]); // do in parallel
+    }
+  }
+
+  function saveAttachment(digest, data, callback) {
+
+
+    var getKeyReq = attachStore.count(digest);
+    getKeyReq.onsuccess = function (e) {
+      var count = e.target.result;
+      if (count) {
+        return callback(); // already exists
+      }
+      var newAtt = {
+        digest: digest,
+        body: data
+      };
+      var putReq = attachStore.put(newAtt);
+      putReq.onsuccess = callback;
+    };
+  }
+}
+
+// Abstraction over IDBCursor and getAll()/getAllKeys() that allows us to batch our operations
+// while falling back to a normal IDBCursor operation on browsers that don't support getAll() or
+// getAllKeys(). This allows for a much faster implementation than just straight-up cursors, because
+// we're not processing each document one-at-a-time.
+function runBatchedCursor(objectStore, keyRange, descending, batchSize, onBatch) {
+
+  if (batchSize === -1) {
+    batchSize = 1000;
+  }
+
+  // Bail out of getAll()/getAllKeys() in the following cases:
+  // 1) either method is unsupported - we need both
+  // 2) batchSize is 1 (might as well use IDBCursor)
+  // 3) descending – no real way to do this via getAll()/getAllKeys()
+
+  var useGetAll = typeof objectStore.getAll === 'function' &&
+    typeof objectStore.getAllKeys === 'function' &&
+    batchSize > 1 && !descending;
+
+  var keysBatch;
+  var valuesBatch;
+  var pseudoCursor;
+
+  function onGetAll(e) {
+    valuesBatch = e.target.result;
+    if (keysBatch) {
+      onBatch(keysBatch, valuesBatch, pseudoCursor);
+    }
+  }
+
+  function onGetAllKeys(e) {
+    keysBatch = e.target.result;
+    if (valuesBatch) {
+      onBatch(keysBatch, valuesBatch, pseudoCursor);
+    }
+  }
+
+  function continuePseudoCursor() {
+    if (!keysBatch.length) { // no more results
+      return onBatch();
+    }
+    // fetch next batch, exclusive start
+    var lastKey = keysBatch[keysBatch.length - 1];
+    var newKeyRange;
+    if (keyRange && keyRange.upper) {
+      try {
+        newKeyRange = IDBKeyRange.bound(lastKey, keyRange.upper,
+          true, keyRange.upperOpen);
+      } catch (e) {
+        if (e.name === "DataError" && e.code === 0) {
+          return onBatch(); // we're done, startkey and endkey are equal
+        }
+      }
+    } else {
+      newKeyRange = IDBKeyRange.lowerBound(lastKey, true);
+    }
+    keyRange = newKeyRange;
+    keysBatch = null;
+    valuesBatch = null;
+    objectStore.getAll(keyRange, batchSize).onsuccess = onGetAll;
+    objectStore.getAllKeys(keyRange, batchSize).onsuccess = onGetAllKeys;
+  }
+
+  function onCursor(e) {
+    var cursor = e.target.result;
+    if (!cursor) { // done
+      return onBatch();
+    }
+    // regular IDBCursor acts like a batch where batch size is always 1
+    onBatch([cursor.key], [cursor.value], cursor);
+  }
+
+  if (useGetAll) {
+    pseudoCursor = {"continue": continuePseudoCursor};
+    objectStore.getAll(keyRange, batchSize).onsuccess = onGetAll;
+    objectStore.getAllKeys(keyRange, batchSize).onsuccess = onGetAllKeys;
+  } else if (descending) {
+    objectStore.openCursor(keyRange, 'prev').onsuccess = onCursor;
+  } else {
+    objectStore.openCursor(keyRange).onsuccess = onCursor;
+  }
+}
+
+// simple shim for objectStore.getAll(), falling back to IDBCursor
+function getAll(objectStore, keyRange, onSuccess) {
+  if (typeof objectStore.getAll === 'function') {
+    // use native getAll
+    objectStore.getAll(keyRange).onsuccess = onSuccess;
+    return;
+  }
+  // fall back to cursors
+  var values = [];
+
+  function onCursor(e) {
+    var cursor = e.target.result;
+    if (cursor) {
+      values.push(cursor.value);
+      cursor["continue"]();
+    } else {
+      onSuccess({
+        target: {
+          result: values
+        }
+      });
+    }
+  }
+
+  objectStore.openCursor(keyRange).onsuccess = onCursor;
+}
+
+function allDocsKeys(keys, docStore, onBatch) {
+  // It's not guaranted to be returned in right order  
+  var valuesBatch = new Array(keys.length);
+  var count = 0;
+  keys.forEach(function (key, index) {
+    docStore.get(key).onsuccess = function (event) {
+      if (event.target.result) {
+        valuesBatch[index] = event.target.result;
+      } else {
+        valuesBatch[index] = {key: key, error: 'not_found'};
+      }
+      count++;
+      if (count === keys.length) {
+        onBatch(keys, valuesBatch, {});
+      }
+    };
+  });
+}
+
+function createKeyRange(start, end, inclusiveEnd, key, descending) {
+  try {
+    if (start && end) {
+      if (descending) {
+        return IDBKeyRange.bound(end, start, !inclusiveEnd, false);
+      } else {
+        return IDBKeyRange.bound(start, end, false, !inclusiveEnd);
+      }
+    } else if (start) {
+      if (descending) {
+        return IDBKeyRange.upperBound(start);
+      } else {
+        return IDBKeyRange.lowerBound(start);
+      }
+    } else if (end) {
+      if (descending) {
+        return IDBKeyRange.lowerBound(end, !inclusiveEnd);
+      } else {
+        return IDBKeyRange.upperBound(end, !inclusiveEnd);
+      }
+    } else if (key) {
+      return IDBKeyRange.only(key);
+    }
+  } catch (e) {
+    return {error: e};
+  }
+  return null;
+}
+
+function idbAllDocs(opts, idb, callback) {
+  var start = 'startkey' in opts ? opts.startkey : false;
+  var end = 'endkey' in opts ? opts.endkey : false;
+  var key = 'key' in opts ? opts.key : false;
+  var keys = 'keys' in opts ? opts.keys : false; 
+  var skip = opts.skip || 0;
+  var limit = typeof opts.limit === 'number' ? opts.limit : -1;
+  var inclusiveEnd = opts.inclusive_end !== false;
+
+  var keyRange ; 
+  var keyRangeError;
+  if (!keys) {
+    keyRange = createKeyRange(start, end, inclusiveEnd, key, opts.descending);
+    keyRangeError = keyRange && keyRange.error;
+    if (keyRangeError && 
+      !(keyRangeError.name === "DataError" && keyRangeError.code === 0)) {
+      // DataError with error code 0 indicates start is less than end, so
+      // can just do an empty query. Else need to throw
+      return callback(createError(IDB_ERROR,
+        keyRangeError.name, keyRangeError.message));
+    }
+  }
+
+  var stores = [DOC_STORE, BY_SEQ_STORE, META_STORE];
+
+  if (opts.attachments) {
+    stores.push(ATTACH_STORE);
+  }
+  var txnResult = openTransactionSafely(idb, stores, 'readonly');
+  if (txnResult.error) {
+    return callback(txnResult.error);
+  }
+  var txn = txnResult.txn;
+  txn.oncomplete = onTxnComplete;
+  txn.onabort = idbError(callback);
+  var docStore = txn.objectStore(DOC_STORE);
+  var seqStore = txn.objectStore(BY_SEQ_STORE);
+  var metaStore = txn.objectStore(META_STORE);
+  var docIdRevIndex = seqStore.index('_doc_id_rev');
+  var results = [];
+  var docCount;
+  var updateSeq;
+
+  metaStore.get(META_STORE).onsuccess = function (e) {
+    docCount = e.target.result.docCount;
+  };
+
+  /* istanbul ignore if */
+  if (opts.update_seq) {
+    getMaxUpdateSeq(seqStore, function (e) { 
+      if (e.target.result && e.target.result.length > 0) {
+        updateSeq = e.target.result[0];
+      }
+    });
+  }
+
+  function getMaxUpdateSeq(objectStore, onSuccess) {
+    function onCursor(e) {
+      var cursor = e.target.result;
+      var maxKey = undefined;
+      if (cursor && cursor.key) {
+        maxKey = cursor.key;
+      } 
+      return onSuccess({
+        target: {
+          result: [maxKey]
+        }
+      });
+    }
+    objectStore.openCursor(null, 'prev').onsuccess = onCursor;
+  }
+
+  // if the user specifies include_docs=true, then we don't
+  // want to block the main cursor while we're fetching the doc
+  function fetchDocAsynchronously(metadata, row, winningRev$$1) {
+    var key = metadata.id + "::" + winningRev$$1;
+    docIdRevIndex.get(key).onsuccess =  function onGetDoc(e) {
+      row.doc = decodeDoc(e.target.result) || {};
+      if (opts.conflicts) {
+        var conflicts = collectConflicts(metadata);
+        if (conflicts.length) {
+          row.doc._conflicts = conflicts;
+        }
+      }
+      fetchAttachmentsIfNecessary(row.doc, opts, txn);
+    };
+  }
+
+  function allDocsInner(winningRev$$1, metadata) {
+    var row = {
+      id: metadata.id,
+      key: metadata.id,
+      value: {
+        rev: winningRev$$1
+      }
+    };
+    var deleted = metadata.deleted;
+    if (deleted) {
+      if (keys) {
+        results.push(row);
+        // deleted docs are okay with "keys" requests
+        row.value.deleted = true;
+        row.doc = null;
+      }
+    } else if (skip-- <= 0) {
+      results.push(row);
+      if (opts.include_docs) {
+        fetchDocAsynchronously(metadata, row, winningRev$$1);
+      }
+    }
+  }
+
+  function processBatch(batchValues) {
+    for (var i = 0, len = batchValues.length; i < len; i++) {
+      if (results.length === limit) {
+        break;
+      }
+      var batchValue = batchValues[i];
+      if (batchValue.error && keys) {
+        // key was not found with "keys" requests
+        results.push(batchValue);
+        continue;
+      }
+      var metadata = decodeMetadata(batchValue);
+      var winningRev$$1 = metadata.winningRev;
+      allDocsInner(winningRev$$1, metadata);
+    }
+  }
+
+  function onBatch(batchKeys, batchValues, cursor) {
+    if (!cursor) {
+      return;
+    }
+    processBatch(batchValues);
+    if (results.length < limit) {
+      cursor["continue"]();
+    }
+  }
+
+  function onGetAll(e) {
+    var values = e.target.result;
+    if (opts.descending) {
+      values = values.reverse();
+    }
+    processBatch(values);
+  }
+
+  function onResultsReady() {
+    var returnVal = {
+      total_rows: docCount,
+      offset: opts.skip,
+      rows: results
+    };
+    
+    /* istanbul ignore if */
+    if (opts.update_seq && updateSeq !== undefined) {
+      returnVal.update_seq = updateSeq;
+    }
+    callback(null, returnVal);
+  }
+
+  function onTxnComplete() {
+    if (opts.attachments) {
+      postProcessAttachments(results, opts.binary).then(onResultsReady);
+    } else {
+      onResultsReady();
+    }
+  }
+
+  // don't bother doing any requests if start > end or limit === 0
+  if (keyRangeError || limit === 0) {
+    return;
+  }
+  if (keys) {
+    return allDocsKeys(opts.keys, docStore, onBatch);
+  }
+  if (limit === -1) { // just fetch everything
+    return getAll(docStore, keyRange, onGetAll);
+  }
+  // else do a cursor
+  // choose a batch size based on the skip, since we'll need to skip that many
+  runBatchedCursor(docStore, keyRange, opts.descending, limit + skip, onBatch);
+}
+
+//
+// Blobs are not supported in all versions of IndexedDB, notably
+// Chrome <37 and Android <5. In those versions, storing a blob will throw.
+//
+// Various other blob bugs exist in Chrome v37-42 (inclusive).
+// Detecting them is expensive and confusing to users, and Chrome 37-42
+// is at very low usage worldwide, so we do a hacky userAgent check instead.
+//
+// content-type bug: https://code.google.com/p/chromium/issues/detail?id=408120
+// 404 bug: https://code.google.com/p/chromium/issues/detail?id=447916
+// FileReader bug: https://code.google.com/p/chromium/issues/detail?id=447836
+//
+function checkBlobSupport(txn) {
+  return new Promise(function (resolve) {
+    var blob$$1 = createBlob(['']);
+    var req = txn.objectStore(DETECT_BLOB_SUPPORT_STORE).put(blob$$1, 'key');
+
+    req.onsuccess = function () {
+      var matchedChrome = navigator.userAgent.match(/Chrome\/(\d+)/);
+      var matchedEdge = navigator.userAgent.match(/Edge\//);
+      // MS Edge pretends to be Chrome 42:
+      // https://msdn.microsoft.com/en-us/library/hh869301%28v=vs.85%29.aspx
+      resolve(matchedEdge || !matchedChrome ||
+        parseInt(matchedChrome[1], 10) >= 43);
+    };
+
+    req.onerror = txn.onabort = function (e) {
+      // If the transaction aborts now its due to not being able to
+      // write to the database, likely due to the disk being full
+      e.preventDefault();
+      e.stopPropagation();
+      resolve(false);
+    };
+  })["catch"](function () {
+    return false; // error, so assume unsupported
+  });
+}
+
+function countDocs(txn, cb) {
+  var index = txn.objectStore(DOC_STORE).index('deletedOrLocal');
+  index.count(IDBKeyRange.only('0')).onsuccess = function (e) {
+    cb(e.target.result);
+  };
+}
+
+// This task queue ensures that IDB open calls are done in their own tick
+
+var running = false;
+var queue = [];
+
+function tryCode(fun, err, res, PouchDB) {
+  try {
+    fun(err, res);
+  } catch (err) {
+    // Shouldn't happen, but in some odd cases
+    // IndexedDB implementations might throw a sync
+    // error, in which case this will at least log it.
+    PouchDB.emit('error', err);
+  }
+}
+
+function applyNext() {
+  if (running || !queue.length) {
+    return;
+  }
+  running = true;
+  queue.shift()();
+}
+
+function enqueueTask(action, callback, PouchDB) {
+  queue.push(function runAction() {
+    action(function runCallback(err, res) {
+      tryCode(callback, err, res, PouchDB);
+      running = false;
+      immediate(function runNext() {
+        applyNext(PouchDB);
+      });
+    });
+  });
+  applyNext();
+}
+
+function changes(opts, api, dbName, idb) {
+  opts = clone(opts);
+
+  if (opts.continuous) {
+    var id = dbName + ':' + uuid();
+    changesHandler.addListener(dbName, id, api, opts);
+    changesHandler.notify(dbName);
+    return {
+      cancel: function () {
+        changesHandler.removeListener(dbName, id);
+      }
+    };
+  }
+
+  var docIds = opts.doc_ids && new ExportedSet(opts.doc_ids);
+
+  opts.since = opts.since || 0;
+  var lastSeq = opts.since;
+
+  var limit = 'limit' in opts ? opts.limit : -1;
+  if (limit === 0) {
+    limit = 1; // per CouchDB _changes spec
+  }
+
+  var results = [];
+  var numResults = 0;
+  var filter = filterChange(opts);
+  var docIdsToMetadata = new ExportedMap();
+
+  var txn;
+  var bySeqStore;
+  var docStore;
+  var docIdRevIndex;
+
+  function onBatch(batchKeys, batchValues, cursor) {
+    if (!cursor || !batchKeys.length) { // done
+      return;
+    }
+
+    var winningDocs = new Array(batchKeys.length);
+    var metadatas = new Array(batchKeys.length);
+
+    function processMetadataAndWinningDoc(metadata, winningDoc) {
+      var change = opts.processChange(winningDoc, metadata, opts);
+      lastSeq = change.seq = metadata.seq;
+
+      var filtered = filter(change);
+      if (typeof filtered === 'object') { // anything but true/false indicates error
+        return Promise.reject(filtered);
+      }
+
+      if (!filtered) {
+        return Promise.resolve();
+      }
+      numResults++;
+      if (opts.return_docs) {
+        results.push(change);
+      }
+      // process the attachment immediately
+      // for the benefit of live listeners
+      if (opts.attachments && opts.include_docs) {
+        return new Promise(function (resolve) {
+          fetchAttachmentsIfNecessary(winningDoc, opts, txn, function () {
+            postProcessAttachments([change], opts.binary).then(function () {
+              resolve(change);
+            });
+          });
+        });
+      } else {
+        return Promise.resolve(change);
+      }
+    }
+
+    function onBatchDone() {
+      var promises = [];
+      for (var i = 0, len = winningDocs.length; i < len; i++) {
+        if (numResults === limit) {
+          break;
+        }
+        var winningDoc = winningDocs[i];
+        if (!winningDoc) {
+          continue;
+        }
+        var metadata = metadatas[i];
+        promises.push(processMetadataAndWinningDoc(metadata, winningDoc));
+      }
+
+      Promise.all(promises).then(function (changes) {
+        for (var i = 0, len = changes.length; i < len; i++) {
+          if (changes[i]) {
+            opts.onChange(changes[i]);
+          }
+        }
+      })["catch"](opts.complete);
+
+      if (numResults !== limit) {
+        cursor["continue"]();
+      }
+    }
+
+    // Fetch all metadatas/winningdocs from this batch in parallel, then process
+    // them all only once all data has been collected. This is done in parallel
+    // because it's faster than doing it one-at-a-time.
+    var numDone = 0;
+    batchValues.forEach(function (value, i) {
+      var doc = decodeDoc(value);
+      var seq = batchKeys[i];
+      fetchWinningDocAndMetadata(doc, seq, function (metadata, winningDoc) {
+        metadatas[i] = metadata;
+        winningDocs[i] = winningDoc;
+        if (++numDone === batchKeys.length) {
+          onBatchDone();
+        }
+      });
+    });
+  }
+
+  function onGetMetadata(doc, seq, metadata, cb) {
+    if (metadata.seq !== seq) {
+      // some other seq is later
+      return cb();
+    }
+
+    if (metadata.winningRev === doc._rev) {
+      // this is the winning doc
+      return cb(metadata, doc);
+    }
+
+    // fetch winning doc in separate request
+    var docIdRev = doc._id + '::' + metadata.winningRev;
+    var req = docIdRevIndex.get(docIdRev);
+    req.onsuccess = function (e) {
+      cb(metadata, decodeDoc(e.target.result));
+    };
+  }
+
+  function fetchWinningDocAndMetadata(doc, seq, cb) {
+    if (docIds && !docIds.has(doc._id)) {
+      return cb();
+    }
+
+    var metadata = docIdsToMetadata.get(doc._id);
+    if (metadata) { // cached
+      return onGetMetadata(doc, seq, metadata, cb);
+    }
+    // metadata not cached, have to go fetch it
+    docStore.get(doc._id).onsuccess = function (e) {
+      metadata = decodeMetadata(e.target.result);
+      docIdsToMetadata.set(doc._id, metadata);
+      onGetMetadata(doc, seq, metadata, cb);
+    };
+  }
+
+  function finish() {
+    opts.complete(null, {
+      results: results,
+      last_seq: lastSeq
+    });
+  }
+
+  function onTxnComplete() {
+    if (!opts.continuous && opts.attachments) {
+      // cannot guarantee that postProcessing was already done,
+      // so do it again
+      postProcessAttachments(results).then(finish);
+    } else {
+      finish();
+    }
+  }
+
+  var objectStores = [DOC_STORE, BY_SEQ_STORE];
+  if (opts.attachments) {
+    objectStores.push(ATTACH_STORE);
+  }
+  var txnResult = openTransactionSafely(idb, objectStores, 'readonly');
+  if (txnResult.error) {
+    return opts.complete(txnResult.error);
+  }
+  txn = txnResult.txn;
+  txn.onabort = idbError(opts.complete);
+  txn.oncomplete = onTxnComplete;
+
+  bySeqStore = txn.objectStore(BY_SEQ_STORE);
+  docStore = txn.objectStore(DOC_STORE);
+  docIdRevIndex = bySeqStore.index('_doc_id_rev');
+
+  var keyRange = (opts.since && !opts.descending) ?
+    IDBKeyRange.lowerBound(opts.since, true) : null;
+
+  runBatchedCursor(bySeqStore, keyRange, opts.descending, limit, onBatch);
+}
+
+var cachedDBs = new ExportedMap();
+var blobSupportPromise;
+var openReqList = new ExportedMap();
+
+function IdbPouch(opts, callback) {
+  var api = this;
+
+  enqueueTask(function (thisCallback) {
+    init(api, opts, thisCallback);
+  }, callback, api.constructor);
+}
+
+function init(api, opts, callback) {
+
+  var dbName = opts.name;
+
+  var idb = null;
+  api._meta = null;
+
+  // called when creating a fresh new database
+  function createSchema(db) {
+    var docStore = db.createObjectStore(DOC_STORE, {keyPath : 'id'});
+    db.createObjectStore(BY_SEQ_STORE, {autoIncrement: true})
+      .createIndex('_doc_id_rev', '_doc_id_rev', {unique: true});
+    db.createObjectStore(ATTACH_STORE, {keyPath: 'digest'});
+    db.createObjectStore(META_STORE, {keyPath: 'id', autoIncrement: false});
+    db.createObjectStore(DETECT_BLOB_SUPPORT_STORE);
+
+    // added in v2
+    docStore.createIndex('deletedOrLocal', 'deletedOrLocal', {unique : false});
+
+    // added in v3
+    db.createObjectStore(LOCAL_STORE, {keyPath: '_id'});
+
+    // added in v4
+    var attAndSeqStore = db.createObjectStore(ATTACH_AND_SEQ_STORE,
+      {autoIncrement: true});
+    attAndSeqStore.createIndex('seq', 'seq');
+    attAndSeqStore.createIndex('digestSeq', 'digestSeq', {unique: true});
+  }
+
+  // migration to version 2
+  // unfortunately "deletedOrLocal" is a misnomer now that we no longer
+  // store local docs in the main doc-store, but whaddyagonnado
+  function addDeletedOrLocalIndex(txn, callback) {
+    var docStore = txn.objectStore(DOC_STORE);
+    docStore.createIndex('deletedOrLocal', 'deletedOrLocal', {unique : false});
+
+    docStore.openCursor().onsuccess = function (event) {
+      var cursor = event.target.result;
+      if (cursor) {
+        var metadata = cursor.value;
+        var deleted = isDeleted(metadata);
+        metadata.deletedOrLocal = deleted ? "1" : "0";
+        docStore.put(metadata);
+        cursor["continue"]();
+      } else {
+        callback();
+      }
+    };
+  }
+
+  // migration to version 3 (part 1)
+  function createLocalStoreSchema(db) {
+    db.createObjectStore(LOCAL_STORE, {keyPath: '_id'})
+      .createIndex('_doc_id_rev', '_doc_id_rev', {unique: true});
+  }
+
+  // migration to version 3 (part 2)
+  function migrateLocalStore(txn, cb) {
+    var localStore = txn.objectStore(LOCAL_STORE);
+    var docStore = txn.objectStore(DOC_STORE);
+    var seqStore = txn.objectStore(BY_SEQ_STORE);
+
+    var cursor = docStore.openCursor();
+    cursor.onsuccess = function (event) {
+      var cursor = event.target.result;
+      if (cursor) {
+        var metadata = cursor.value;
+        var docId = metadata.id;
+        var local = isLocalId(docId);
+        var rev$$1 = winningRev(metadata);
+        if (local) {
+          var docIdRev = docId + "::" + rev$$1;
+          // remove all seq entries
+          // associated with this docId
+          var start = docId + "::";
+          var end = docId + "::~";
+          var index = seqStore.index('_doc_id_rev');
+          var range = IDBKeyRange.bound(start, end, false, false);
+          var seqCursor = index.openCursor(range);
+          seqCursor.onsuccess = function (e) {
+            seqCursor = e.target.result;
+            if (!seqCursor) {
+              // done
+              docStore["delete"](cursor.primaryKey);
+              cursor["continue"]();
+            } else {
+              var data = seqCursor.value;
+              if (data._doc_id_rev === docIdRev) {
+                localStore.put(data);
+              }
+              seqStore["delete"](seqCursor.primaryKey);
+              seqCursor["continue"]();
+            }
+          };
+        } else {
+          cursor["continue"]();
+        }
+      } else if (cb) {
+        cb();
+      }
+    };
+  }
+
+  // migration to version 4 (part 1)
+  function addAttachAndSeqStore(db) {
+    var attAndSeqStore = db.createObjectStore(ATTACH_AND_SEQ_STORE,
+      {autoIncrement: true});
+    attAndSeqStore.createIndex('seq', 'seq');
+    attAndSeqStore.createIndex('digestSeq', 'digestSeq', {unique: true});
+  }
+
+  // migration to version 4 (part 2)
+  function migrateAttsAndSeqs(txn, callback) {
+    var seqStore = txn.objectStore(BY_SEQ_STORE);
+    var attStore = txn.objectStore(ATTACH_STORE);
+    var attAndSeqStore = txn.objectStore(ATTACH_AND_SEQ_STORE);
+
+    // need to actually populate the table. this is the expensive part,
+    // so as an optimization, check first that this database even
+    // contains attachments
+    var req = attStore.count();
+    req.onsuccess = function (e) {
+      var count = e.target.result;
+      if (!count) {
+        return callback(); // done
+      }
+
+      seqStore.openCursor().onsuccess = function (e) {
+        var cursor = e.target.result;
+        if (!cursor) {
+          return callback(); // done
+        }
+        var doc = cursor.value;
+        var seq = cursor.primaryKey;
+        var atts = Object.keys(doc._attachments || {});
+        var digestMap = {};
+        for (var j = 0; j < atts.length; j++) {
+          var att = doc._attachments[atts[j]];
+          digestMap[att.digest] = true; // uniq digests, just in case
+        }
+        var digests = Object.keys(digestMap);
+        for (j = 0; j < digests.length; j++) {
+          var digest = digests[j];
+          attAndSeqStore.put({
+            seq: seq,
+            digestSeq: digest + '::' + seq
+          });
+        }
+        cursor["continue"]();
+      };
+    };
+  }
+
+  // migration to version 5
+  // Instead of relying on on-the-fly migration of metadata,
+  // this brings the doc-store to its modern form:
+  // - metadata.winningrev
+  // - metadata.seq
+  // - stringify the metadata when storing it
+  function migrateMetadata(txn) {
+
+    function decodeMetadataCompat(storedObject) {
+      if (!storedObject.data) {
+        // old format, when we didn't store it stringified
+        storedObject.deleted = storedObject.deletedOrLocal === '1';
+        return storedObject;
+      }
+      return decodeMetadata(storedObject);
+    }
+
+    // ensure that every metadata has a winningRev and seq,
+    // which was previously created on-the-fly but better to migrate
+    var bySeqStore = txn.objectStore(BY_SEQ_STORE);
+    var docStore = txn.objectStore(DOC_STORE);
+    var cursor = docStore.openCursor();
+    cursor.onsuccess = function (e) {
+      var cursor = e.target.result;
+      if (!cursor) {
+        return; // done
+      }
+      var metadata = decodeMetadataCompat(cursor.value);
+
+      metadata.winningRev = metadata.winningRev ||
+        winningRev(metadata);
+
+      function fetchMetadataSeq() {
+        // metadata.seq was added post-3.2.0, so if it's missing,
+        // we need to fetch it manually
+        var start = metadata.id + '::';
+        var end = metadata.id + '::\uffff';
+        var req = bySeqStore.index('_doc_id_rev').openCursor(
+          IDBKeyRange.bound(start, end));
+
+        var metadataSeq = 0;
+        req.onsuccess = function (e) {
+          var cursor = e.target.result;
+          if (!cursor) {
+            metadata.seq = metadataSeq;
+            return onGetMetadataSeq();
+          }
+          var seq = cursor.primaryKey;
+          if (seq > metadataSeq) {
+            metadataSeq = seq;
+          }
+          cursor["continue"]();
+        };
+      }
+
+      function onGetMetadataSeq() {
+        var metadataToStore = encodeMetadata(metadata,
+          metadata.winningRev, metadata.deleted);
+
+        var req = docStore.put(metadataToStore);
+        req.onsuccess = function () {
+          cursor["continue"]();
+        };
+      }
+
+      if (metadata.seq) {
+        return onGetMetadataSeq();
+      }
+
+      fetchMetadataSeq();
+    };
+
+  }
+
+  api._remote = false;
+  api.type = function () {
+    return 'idb';
+  };
+
+  api._id = toPromise(function (callback) {
+    callback(null, api._meta.instanceId);
+  });
+
+  api._bulkDocs = function idb_bulkDocs(req, reqOpts, callback) {
+    idbBulkDocs(opts, req, reqOpts, api, idb, callback);
+  };
+
+  // First we look up the metadata in the ids database, then we fetch the
+  // current revision(s) from the by sequence store
+  api._get = function idb_get(id, opts, callback) {
+    var doc;
+    var metadata;
+    var err;
+    var txn = opts.ctx;
+    if (!txn) {
+      var txnResult = openTransactionSafely(idb,
+        [DOC_STORE, BY_SEQ_STORE, ATTACH_STORE], 'readonly');
+      if (txnResult.error) {
+        return callback(txnResult.error);
+      }
+      txn = txnResult.txn;
+    }
+
+    function finish() {
+      callback(err, {doc: doc, metadata: metadata, ctx: txn});
+    }
+
+    txn.objectStore(DOC_STORE).get(id).onsuccess = function (e) {
+      metadata = decodeMetadata(e.target.result);
+      // we can determine the result here if:
+      // 1. there is no such document
+      // 2. the document is deleted and we don't ask about specific rev
+      // When we ask with opts.rev we expect the answer to be either
+      // doc (possibly with _deleted=true) or missing error
+      if (!metadata) {
+        err = createError(MISSING_DOC, 'missing');
+        return finish();
+      }
+
+      var rev$$1;
+      if (!opts.rev) {
+        rev$$1 = metadata.winningRev;
+        var deleted = isDeleted(metadata);
+        if (deleted) {
+          err = createError(MISSING_DOC, "deleted");
+          return finish();
+        }
+      } else {
+        rev$$1 = opts.latest ? latest(opts.rev, metadata) : opts.rev;
+      }
+
+      var objectStore = txn.objectStore(BY_SEQ_STORE);
+      var key = metadata.id + '::' + rev$$1;
+
+      objectStore.index('_doc_id_rev').get(key).onsuccess = function (e) {
+        doc = e.target.result;
+        if (doc) {
+          doc = decodeDoc(doc);
+        }
+        if (!doc) {
+          err = createError(MISSING_DOC, 'missing');
+          return finish();
+        }
+        finish();
+      };
+    };
+  };
+
+  api._getAttachment = function (docId, attachId, attachment, opts, callback) {
+    var txn;
+    if (opts.ctx) {
+      txn = opts.ctx;
+    } else {
+      var txnResult = openTransactionSafely(idb,
+        [DOC_STORE, BY_SEQ_STORE, ATTACH_STORE], 'readonly');
+      if (txnResult.error) {
+        return callback(txnResult.error);
+      }
+      txn = txnResult.txn;
+    }
+    var digest = attachment.digest;
+    var type = attachment.content_type;
+
+    txn.objectStore(ATTACH_STORE).get(digest).onsuccess = function (e) {
+      var body = e.target.result.body;
+      readBlobData(body, type, opts.binary, function (blobData) {
+        callback(null, blobData);
+      });
+    };
+  };
+
+  api._info = function idb_info(callback) {
+    var updateSeq;
+    var docCount;
+
+    var txnResult = openTransactionSafely(idb, [META_STORE, BY_SEQ_STORE], 'readonly');
+    if (txnResult.error) {
+      return callback(txnResult.error);
+    }
+    var txn = txnResult.txn;
+    txn.objectStore(META_STORE).get(META_STORE).onsuccess = function (e) {
+      docCount = e.target.result.docCount;
+    };
+    txn.objectStore(BY_SEQ_STORE).openCursor(null, 'prev').onsuccess = function (e) {
+      var cursor = e.target.result;
+      updateSeq = cursor ? cursor.key : 0;
+    };
+
+    txn.oncomplete = function () {
+      callback(null, {
+        doc_count: docCount,
+        update_seq: updateSeq,
+        // for debugging
+        idb_attachment_format: (api._meta.blobSupport ? 'binary' : 'base64')
+      });
+    };
+  };
+
+  api._allDocs = function idb_allDocs(opts, callback) {
+    idbAllDocs(opts, idb, callback);
+  };
+
+  api._changes = function idbChanges(opts) {
+    return changes(opts, api, dbName, idb);
+  };
+
+  api._close = function (callback) {
+    // https://developer.mozilla.org/en-US/docs/IndexedDB/IDBDatabase#close
+    // "Returns immediately and closes the connection in a separate thread..."
+    idb.close();
+    cachedDBs["delete"](dbName);
+    callback();
+  };
+
+  api._getRevisionTree = function (docId, callback) {
+    var txnResult = openTransactionSafely(idb, [DOC_STORE], 'readonly');
+    if (txnResult.error) {
+      return callback(txnResult.error);
+    }
+    var txn = txnResult.txn;
+    var req = txn.objectStore(DOC_STORE).get(docId);
+    req.onsuccess = function (event) {
+      var doc = decodeMetadata(event.target.result);
+      if (!doc) {
+        callback(createError(MISSING_DOC));
+      } else {
+        callback(null, doc.rev_tree);
+      }
+    };
+  };
+
+  // This function removes revisions of document docId
+  // which are listed in revs and sets this document
+  // revision to to rev_tree
+  api._doCompaction = function (docId, revs, callback) {
+    var stores = [
+      DOC_STORE,
+      BY_SEQ_STORE,
+      ATTACH_STORE,
+      ATTACH_AND_SEQ_STORE
+    ];
+    var txnResult = openTransactionSafely(idb, stores, 'readwrite');
+    if (txnResult.error) {
+      return callback(txnResult.error);
+    }
+    var txn = txnResult.txn;
+
+    var docStore = txn.objectStore(DOC_STORE);
+
+    docStore.get(docId).onsuccess = function (event) {
+      var metadata = decodeMetadata(event.target.result);
+      traverseRevTree(metadata.rev_tree, function (isLeaf, pos,
+                                                         revHash, ctx, opts) {
+        var rev$$1 = pos + '-' + revHash;
+        if (revs.indexOf(rev$$1) !== -1) {
+          opts.status = 'missing';
+        }
+      });
+      compactRevs(revs, docId, txn);
+      var winningRev$$1 = metadata.winningRev;
+      var deleted = metadata.deleted;
+      txn.objectStore(DOC_STORE).put(
+        encodeMetadata(metadata, winningRev$$1, deleted));
+    };
+    txn.onabort = idbError(callback);
+    txn.oncomplete = function () {
+      callback();
+    };
+  };
+
+
+  api._getLocal = function (id, callback) {
+    var txnResult = openTransactionSafely(idb, [LOCAL_STORE], 'readonly');
+    if (txnResult.error) {
+      return callback(txnResult.error);
+    }
+    var tx = txnResult.txn;
+    var req = tx.objectStore(LOCAL_STORE).get(id);
+
+    req.onerror = idbError(callback);
+    req.onsuccess = function (e) {
+      var doc = e.target.result;
+      if (!doc) {
+        callback(createError(MISSING_DOC));
+      } else {
+        delete doc['_doc_id_rev']; // for backwards compat
+        callback(null, doc);
+      }
+    };
+  };
+
+  api._putLocal = function (doc, opts, callback) {
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+    delete doc._revisions; // ignore this, trust the rev
+    var oldRev = doc._rev;
+    var id = doc._id;
+    if (!oldRev) {
+      doc._rev = '0-1';
+    } else {
+      doc._rev = '0-' + (parseInt(oldRev.split('-')[1], 10) + 1);
+    }
+
+    var tx = opts.ctx;
+    var ret;
+    if (!tx) {
+      var txnResult = openTransactionSafely(idb, [LOCAL_STORE], 'readwrite');
+      if (txnResult.error) {
+        return callback(txnResult.error);
+      }
+      tx = txnResult.txn;
+      tx.onerror = idbError(callback);
+      tx.oncomplete = function () {
+        if (ret) {
+          callback(null, ret);
+        }
+      };
+    }
+
+    var oStore = tx.objectStore(LOCAL_STORE);
+    var req;
+    if (oldRev) {
+      req = oStore.get(id);
+      req.onsuccess = function (e) {
+        var oldDoc = e.target.result;
+        if (!oldDoc || oldDoc._rev !== oldRev) {
+          callback(createError(REV_CONFLICT));
+        } else { // update
+          var req = oStore.put(doc);
+          req.onsuccess = function () {
+            ret = {ok: true, id: doc._id, rev: doc._rev};
+            if (opts.ctx) { // return immediately
+              callback(null, ret);
+            }
+          };
+        }
+      };
+    } else { // new doc
+      req = oStore.add(doc);
+      req.onerror = function (e) {
+        // constraint error, already exists
+        callback(createError(REV_CONFLICT));
+        e.preventDefault(); // avoid transaction abort
+        e.stopPropagation(); // avoid transaction onerror
+      };
+      req.onsuccess = function () {
+        ret = {ok: true, id: doc._id, rev: doc._rev};
+        if (opts.ctx) { // return immediately
+          callback(null, ret);
+        }
+      };
+    }
+  };
+
+  api._removeLocal = function (doc, opts, callback) {
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+    var tx = opts.ctx;
+    if (!tx) {
+      var txnResult = openTransactionSafely(idb, [LOCAL_STORE], 'readwrite');
+      if (txnResult.error) {
+        return callback(txnResult.error);
+      }
+      tx = txnResult.txn;
+      tx.oncomplete = function () {
+        if (ret) {
+          callback(null, ret);
+        }
+      };
+    }
+    var ret;
+    var id = doc._id;
+    var oStore = tx.objectStore(LOCAL_STORE);
+    var req = oStore.get(id);
+
+    req.onerror = idbError(callback);
+    req.onsuccess = function (e) {
+      var oldDoc = e.target.result;
+      if (!oldDoc || oldDoc._rev !== doc._rev) {
+        callback(createError(MISSING_DOC));
+      } else {
+        oStore["delete"](id);
+        ret = {ok: true, id: id, rev: '0-0'};
+        if (opts.ctx) { // return immediately
+          callback(null, ret);
+        }
+      }
+    };
+  };
+
+  api._destroy = function (opts, callback) {
+    changesHandler.removeAllListeners(dbName);
+
+    //Close open request for "dbName" database to fix ie delay.
+    var openReq = openReqList.get(dbName);
+    if (openReq && openReq.result) {
+      openReq.result.close();
+      cachedDBs["delete"](dbName);
+    }
+    var req = indexedDB.deleteDatabase(dbName);
+
+    req.onsuccess = function () {
+      //Remove open request from the list.
+      openReqList["delete"](dbName);
+      if (hasLocalStorage() && (dbName in localStorage)) {
+        delete localStorage[dbName];
+      }
+      callback(null, { 'ok': true });
+    };
+
+    req.onerror = idbError(callback);
+  };
+
+  var cached = cachedDBs.get(dbName);
+
+  if (cached) {
+    idb = cached.idb;
+    api._meta = cached.global;
+    return immediate(function () {
+      callback(null, api);
+    });
+  }
+
+  var req = indexedDB.open(dbName, ADAPTER_VERSION);
+  openReqList.set(dbName, req);
+
+  req.onupgradeneeded = function (e) {
+    var db = e.target.result;
+    if (e.oldVersion < 1) {
+      return createSchema(db); // new db, initial schema
+    }
+    // do migrations
+
+    var txn = e.currentTarget.transaction;
+    // these migrations have to be done in this function, before
+    // control is returned to the event loop, because IndexedDB
+
+    if (e.oldVersion < 3) {
+      createLocalStoreSchema(db); // v2 -> v3
+    }
+    if (e.oldVersion < 4) {
+      addAttachAndSeqStore(db); // v3 -> v4
+    }
+
+    var migrations = [
+      addDeletedOrLocalIndex, // v1 -> v2
+      migrateLocalStore,      // v2 -> v3
+      migrateAttsAndSeqs,     // v3 -> v4
+      migrateMetadata         // v4 -> v5
+    ];
+
+    var i = e.oldVersion;
+
+    function next() {
+      var migration = migrations[i - 1];
+      i++;
+      if (migration) {
+        migration(txn, next);
+      }
+    }
+
+    next();
+  };
+
+  req.onsuccess = function (e) {
+
+    idb = e.target.result;
+
+    idb.onversionchange = function () {
+      idb.close();
+      cachedDBs["delete"](dbName);
+    };
+
+    idb.onabort = function (e) {
+      guardedConsole('error', 'Database has a global failure', e.target.error);
+      idb.close();
+      cachedDBs["delete"](dbName);
+    };
+
+    // Do a few setup operations (in parallel as much as possible):
+    // 1. Fetch meta doc
+    // 2. Check blob support
+    // 3. Calculate docCount
+    // 4. Generate an instanceId if necessary
+    // 5. Store docCount and instanceId on meta doc
+
+    var txn = idb.transaction([
+      META_STORE,
+      DETECT_BLOB_SUPPORT_STORE,
+      DOC_STORE
+    ], 'readwrite');
+
+    var storedMetaDoc = false;
+    var metaDoc;
+    var docCount;
+    var blobSupport;
+    var instanceId;
+
+    function completeSetup() {
+      if (typeof blobSupport === 'undefined' || !storedMetaDoc) {
+        return;
+      }
+      api._meta = {
+        name: dbName,
+        instanceId: instanceId,
+        blobSupport: blobSupport
+      };
+
+      cachedDBs.set(dbName, {
+        idb: idb,
+        global: api._meta
+      });
+      callback(null, api);
+    }
+
+    function storeMetaDocIfReady() {
+      if (typeof docCount === 'undefined' || typeof metaDoc === 'undefined') {
+        return;
+      }
+      var instanceKey = dbName + '_id';
+      if (instanceKey in metaDoc) {
+        instanceId = metaDoc[instanceKey];
+      } else {
+        metaDoc[instanceKey] = instanceId = uuid();
+      }
+      metaDoc.docCount = docCount;
+      txn.objectStore(META_STORE).put(metaDoc);
+    }
+
+    //
+    // fetch or generate the instanceId
+    //
+    txn.objectStore(META_STORE).get(META_STORE).onsuccess = function (e) {
+      metaDoc = e.target.result || { id: META_STORE };
+      storeMetaDocIfReady();
+    };
+
+    //
+    // countDocs
+    //
+    countDocs(txn, function (count) {
+      docCount = count;
+      storeMetaDocIfReady();
+    });
+
+    //
+    // check blob support
+    //
+    if (!blobSupportPromise) {
+      // make sure blob support is only checked once
+      blobSupportPromise = checkBlobSupport(txn);
+    }
+
+    blobSupportPromise.then(function (val) {
+      blobSupport = val;
+      completeSetup();
+    });
+
+    // only when the metadata put transaction has completed,
+    // consider the setup done
+    txn.oncomplete = function () {
+      storedMetaDoc = true;
+      completeSetup();
+    };
+    txn.onabort = idbError(callback);
+  };
+
+  req.onerror = function () {
+    var msg = 'Failed to open indexedDB, are you in private browsing mode?';
+    guardedConsole('error', msg);
+    callback(createError(IDB_ERROR, msg));
+  };
+}
+
+IdbPouch.valid = function () {
+  // Following #7085 buggy idb versions (typically Safari < 10.1) are
+  // considered valid.
+
+  // On Firefox SecurityError is thrown while referencing indexedDB if cookies
+  // are not allowed. `typeof indexedDB` also triggers the error.
+  try {
+    // some outdated implementations of IDB that appear on Samsung
+    // and HTC Android devices <4.4 are missing IDBKeyRange
+    return typeof indexedDB !== 'undefined' && typeof IDBKeyRange !== 'undefined';
+  } catch (e) {
+    return false;
+  }
+};
+
+function IDBPouch (PouchDB) {
+  PouchDB.adapter('idb', IdbPouch, true);
+}
+
+// dead simple promise pool, inspired by https://github.com/timdp/es6-promise-pool
+// but much smaller in code size. limits the number of concurrent promises that are executed
+
+
+function pool(promiseFactories, limit) {
+  return new Promise(function (resolve, reject) {
+    var running = 0;
+    var current = 0;
+    var done = 0;
+    var len = promiseFactories.length;
+    var err;
+
+    function runNext() {
+      running++;
+      promiseFactories[current++]().then(onSuccess, onError);
+    }
+
+    function doNext() {
+      if (++done === len) {
+        /* istanbul ignore if */
+        if (err) {
+          reject(err);
+        } else {
+          resolve();
+        }
+      } else {
+        runNextBatch();
+      }
+    }
+
+    function onSuccess() {
+      running--;
+      doNext();
+    }
+
+    /* istanbul ignore next */
+    function onError(thisErr) {
+      running--;
+      err = err || thisErr;
+      doNext();
+    }
+
+    function runNextBatch() {
+      while (running < limit && current < len) {
+        runNext();
+      }
+    }
+
+    runNextBatch();
+  });
+}
+
+var CHANGES_BATCH_SIZE = 25;
+var MAX_SIMULTANEOUS_REVS = 50;
+var CHANGES_TIMEOUT_BUFFER = 5000;
+var DEFAULT_HEARTBEAT = 10000;
+
+var supportsBulkGetMap = {};
+
+function readAttachmentsAsBlobOrBuffer(row) {
+  var doc = row.doc || row.ok;
+  var atts = doc && doc._attachments;
+  if (!atts) {
+    return;
+  }
+  Object.keys(atts).forEach(function (filename) {
+    var att = atts[filename];
+    att.data = b64ToBluffer(att.data, att.content_type);
+  });
+}
+
+function encodeDocId(id) {
+  if (/^_design/.test(id)) {
+    return '_design/' + encodeURIComponent(id.slice(8));
+  }
+  if (/^_local/.test(id)) {
+    return '_local/' + encodeURIComponent(id.slice(7));
+  }
+  return encodeURIComponent(id);
+}
+
+function preprocessAttachments$1(doc) {
+  if (!doc._attachments || !Object.keys(doc._attachments)) {
+    return Promise.resolve();
+  }
+
+  return Promise.all(Object.keys(doc._attachments).map(function (key) {
+    var attachment = doc._attachments[key];
+    if (attachment.data && typeof attachment.data !== 'string') {
+      return new Promise(function (resolve) {
+        blobToBase64(attachment.data, resolve);
+      }).then(function (b64) {
+        attachment.data = b64;
+      });
+    }
+  }));
+}
+
+function hasUrlPrefix(opts) {
+  if (!opts.prefix) {
+    return false;
+  }
+  var protocol = parseUri(opts.prefix).protocol;
+  return protocol === 'http' || protocol === 'https';
+}
+
+// Get all the information you possibly can about the URI given by name and
+// return it as a suitable object.
+function getHost(name, opts) {
+  // encode db name if opts.prefix is a url (#5574)
+  if (hasUrlPrefix(opts)) {
+    var dbName = opts.name.substr(opts.prefix.length);
+    // Ensure prefix has a trailing slash
+    var prefix = opts.prefix.replace(/\/?$/, '/');
+    name = prefix + encodeURIComponent(dbName);
+  }
+
+  var uri = parseUri(name);
+  if (uri.user || uri.password) {
+    uri.auth = {username: uri.user, password: uri.password};
+  }
+
+  // Split the path part of the URI into parts using '/' as the delimiter
+  // after removing any leading '/' and any trailing '/'
+  var parts = uri.path.replace(/(^\/|\/$)/g, '').split('/');
+
+  uri.db = parts.pop();
+  // Prevent double encoding of URI component
+  if (uri.db.indexOf('%') === -1) {
+    uri.db = encodeURIComponent(uri.db);
+  }
+
+  uri.path = parts.join('/');
+
+  return uri;
+}
+
+// Generate a URL with the host data given by opts and the given path
+function genDBUrl(opts, path) {
+  return genUrl(opts, opts.db + '/' + path);
+}
+
+// Generate a URL with the host data given by opts and the given path
+function genUrl(opts, path) {
+  // If the host already has a path, then we need to have a path delimiter
+  // Otherwise, the path delimiter is the empty string
+  var pathDel = !opts.path ? '' : '/';
+
+  // If the host already has a path, then we need to have a path delimiter
+  // Otherwise, the path delimiter is the empty string
+  return opts.protocol + '://' + opts.host +
+         (opts.port ? (':' + opts.port) : '') +
+         '/' + opts.path + pathDel + path;
+}
+
+function paramsToStr(params) {
+  return '?' + Object.keys(params).map(function (k) {
+    return k + '=' + encodeURIComponent(params[k]);
+  }).join('&');
+}
+
+function shouldCacheBust(opts) {
+  var ua = (typeof navigator !== 'undefined' && navigator.userAgent) ?
+      navigator.userAgent.toLowerCase() : '';
+  var isIE = ua.indexOf('msie') !== -1;
+  var isTrident = ua.indexOf('trident') !== -1;
+  var isEdge = ua.indexOf('edge') !== -1;
+  var isGET = !('method' in opts) || opts.method === 'GET';
+  return (isIE || isTrident || isEdge) && isGET;
+}
+
+// Implements the PouchDB API for dealing with CouchDB instances over HTTP
+function HttpPouch(opts, callback) {
+
+  // The functions that will be publicly available for HttpPouch
+  var api = this;
+
+  var host = getHost(opts.name, opts);
+  var dbUrl = genDBUrl(host, '');
+
+  opts = clone(opts);
+
+  var ourFetch = function (url, options) {
+
+    options = options || {};
+    options.headers = options.headers || new h();
+
+    options.credentials = 'include';
+
+    if (opts.auth || host.auth) {
+      var nAuth = opts.auth || host.auth;
+      var str = nAuth.username + ':' + nAuth.password;
+      var token = thisBtoa(unescape(encodeURIComponent(str)));
+      options.headers.set('Authorization', 'Basic ' + token);
+    }
+
+    var headers = opts.headers || {};
+    Object.keys(headers).forEach(function (key) {
+      options.headers.append(key, headers[key]);
+    });
+
+    /* istanbul ignore if */
+    if (shouldCacheBust(options)) {
+      url += (url.indexOf('?') === -1 ? '?' : '&') + '_nonce=' + Date.now();
+    }
+
+    var fetchFun = opts.fetch || f$1;
+    return fetchFun(url, options);
+  };
+
+  function adapterFun$$1(name, fun) {
+    return adapterFun(name, getArguments(function (args) {
+      setup().then(function () {
+        return fun.apply(this, args);
+      })["catch"](function (e) {
+        var callback = args.pop();
+        callback(e);
+      });
+    })).bind(api);
+  }
+
+  function fetchJSON(url, options, callback) {
+
+    var result = {};
+
+    options = options || {};
+    options.headers = options.headers || new h();
+
+    if (!options.headers.get('Content-Type')) {
+      options.headers.set('Content-Type', 'application/json');
+    }
+    if (!options.headers.get('Accept')) {
+      options.headers.set('Accept', 'application/json');
+    }
+
+    return ourFetch(url, options).then(function (response) {
+      result.ok = response.ok;
+      result.status = response.status;
+      return response.json();
+    }).then(function (json) {
+      result.data = json;
+      if (!result.ok) {
+        result.data.status = result.status;
+        var err = generateErrorFromResponse(result.data);
+        if (callback) {
+          return callback(err);
+        } else {
+          throw err;
+        }
+      }
+
+      if (Array.isArray(result.data)) {
+        result.data = result.data.map(function (v) {
+          if (v.error || v.missing) {
+            return generateErrorFromResponse(v);
+          } else {
+            return v;
+          }
+        });
+      }
+
+      if (callback) {
+        callback(null, result.data);
+      } else {
+        return result;
+      }
+    });
+  }
+
+  var setupPromise;
+
+  function setup() {
+    if (opts.skip_setup) {
+      return Promise.resolve();
+    }
+
+    // If there is a setup in process or previous successful setup
+    // done then we will use that
+    // If previous setups have been rejected we will try again
+    if (setupPromise) {
+      return setupPromise;
+    }
+
+    setupPromise = fetchJSON(dbUrl)["catch"](function (err) {
+      if (err && err.status && err.status === 404) {
+        // Doesnt exist, create it
+        explainError(404, 'PouchDB is just detecting if the remote exists.');
+        return fetchJSON(dbUrl, {method: 'PUT'});
+      } else {
+        return Promise.reject(err);
+      }
+    })["catch"](function (err) {
+      // If we try to create a database that already exists, skipped in
+      // istanbul since its catching a race condition.
+      /* istanbul ignore if */
+      if (err && err.status && err.status === 412) {
+        return true;
+      }
+      return Promise.reject(err);
+    });
+
+    setupPromise["catch"](function () {
+      setupPromise = null;
+    });
+
+    return setupPromise;
+  }
+
+  immediate(function () {
+    callback(null, api);
+  });
+
+  api._remote = true;
+
+  /* istanbul ignore next */
+  api.type = function () {
+    return 'http';
+  };
+
+  api.id = adapterFun$$1('id', function (callback) {
+    ourFetch(genUrl(host, '')).then(function (response) {
+      return response.json();
+    })["catch"](function () {
+      return {};
+    }).then(function (result) {
+      // Bad response or missing `uuid` should not prevent ID generation.
+      var uuid$$1 = (result && result.uuid) ?
+          (result.uuid + host.db) : genDBUrl(host, '');
+      callback(null, uuid$$1);
+    });
+  });
+
+  // Sends a POST request to the host calling the couchdb _compact function
+  //    version: The version of CouchDB it is running
+  api.compact = adapterFun$$1('compact', function (opts, callback) {
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+    opts = clone(opts);
+
+    fetchJSON(genDBUrl(host, '_compact'), {method: 'POST'}).then(function () {
+      function ping() {
+        api.info(function (err, res) {
+          // CouchDB may send a "compact_running:true" if it's
+          // already compacting. PouchDB Server doesn't.
+          /* istanbul ignore else */
+          if (res && !res.compact_running) {
+            callback(null, {ok: true});
+          } else {
+            setTimeout(ping, opts.interval || 200);
+          }
+        });
+      }
+      // Ping the http if it's finished compaction
+      ping();
+    });
+  });
+
+  api.bulkGet = adapterFun('bulkGet', function (opts, callback) {
+    var self = this;
+
+    function doBulkGet(cb) {
+      var params = {};
+      if (opts.revs) {
+        params.revs = true;
+      }
+      if (opts.attachments) {
+        /* istanbul ignore next */
+        params.attachments = true;
+      }
+      if (opts.latest) {
+        params.latest = true;
+      }
+      fetchJSON(genDBUrl(host, '_bulk_get' + paramsToStr(params)), {
+        method: 'POST',
+        body: JSON.stringify({ docs: opts.docs})
+      }).then(function (result) {
+        if (opts.attachments && opts.binary) {
+          result.data.results.forEach(function (res) {
+            res.docs.forEach(readAttachmentsAsBlobOrBuffer);
+          });
+        }
+        cb(null, result.data);
+      })["catch"](cb);
+    }
+
+    /* istanbul ignore next */
+    function doBulkGetShim() {
+      // avoid "url too long error" by splitting up into multiple requests
+      var batchSize = MAX_SIMULTANEOUS_REVS;
+      var numBatches = Math.ceil(opts.docs.length / batchSize);
+      var numDone = 0;
+      var results = new Array(numBatches);
+
+      function onResult(batchNum) {
+        return function (err, res) {
+          // err is impossible because shim returns a list of errs in that case
+          results[batchNum] = res.results;
+          if (++numDone === numBatches) {
+            callback(null, {results: flatten(results)});
+          }
+        };
+      }
+
+      for (var i = 0; i < numBatches; i++) {
+        var subOpts = pick(opts, ['revs', 'attachments', 'binary', 'latest']);
+        subOpts.docs = opts.docs.slice(i * batchSize,
+          Math.min(opts.docs.length, (i + 1) * batchSize));
+        bulkGet(self, subOpts, onResult(i));
+      }
+    }
+
+    // mark the whole database as either supporting or not supporting _bulk_get
+    var dbUrl = genUrl(host, '');
+    var supportsBulkGet = supportsBulkGetMap[dbUrl];
+
+    /* istanbul ignore next */
+    if (typeof supportsBulkGet !== 'boolean') {
+      // check if this database supports _bulk_get
+      doBulkGet(function (err, res) {
+        if (err) {
+          supportsBulkGetMap[dbUrl] = false;
+          explainError(
+            err.status,
+            'PouchDB is just detecting if the remote ' +
+            'supports the _bulk_get API.'
+          );
+          doBulkGetShim();
+        } else {
+          supportsBulkGetMap[dbUrl] = true;
+          callback(null, res);
+        }
+      });
+    } else if (supportsBulkGet) {
+      doBulkGet(callback);
+    } else {
+      doBulkGetShim();
+    }
+  });
+
+  // Calls GET on the host, which gets back a JSON string containing
+  //    couchdb: A welcome string
+  //    version: The version of CouchDB it is running
+  api._info = function (callback) {
+    setup().then(function () {
+      return ourFetch(genDBUrl(host, ''));
+    }).then(function (response) {
+      return response.json();
+    }).then(function (info) {
+      info.host = genDBUrl(host, '');
+      callback(null, info);
+    })["catch"](callback);
+  };
+
+  api.fetch = function (path, options) {
+    return setup().then(function () {
+      var url = path.substring(0, 1) === '/' ?
+        genUrl(host, path.substring(1)) :
+        genDBUrl(host, path);
+      return ourFetch(url, options);
+    });
+  };
+
+  // Get the document with the given id from the database given by host.
+  // The id could be solely the _id in the database, or it may be a
+  // _design/ID or _local/ID path
+  api.get = adapterFun$$1('get', function (id, opts, callback) {
+    // If no options were given, set the callback to the second parameter
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+    opts = clone(opts);
+
+    // List of parameters to add to the GET request
+    var params = {};
+
+    if (opts.revs) {
+      params.revs = true;
+    }
+
+    if (opts.revs_info) {
+      params.revs_info = true;
+    }
+
+    if (opts.latest) {
+      params.latest = true;
+    }
+
+    if (opts.open_revs) {
+      if (opts.open_revs !== "all") {
+        opts.open_revs = JSON.stringify(opts.open_revs);
+      }
+      params.open_revs = opts.open_revs;
+    }
+
+    if (opts.rev) {
+      params.rev = opts.rev;
+    }
+
+    if (opts.conflicts) {
+      params.conflicts = opts.conflicts;
+    }
+
+    /* istanbul ignore if */
+    if (opts.update_seq) {
+      params.update_seq = opts.update_seq;
+    }
+
+    id = encodeDocId(id);
+
+    function fetchAttachments(doc) {
+      var atts = doc._attachments;
+      var filenames = atts && Object.keys(atts);
+      if (!atts || !filenames.length) {
+        return;
+      }
+      // we fetch these manually in separate XHRs, because
+      // Sync Gateway would normally send it back as multipart/mixed,
+      // which we cannot parse. Also, this is more efficient than
+      // receiving attachments as base64-encoded strings.
+      function fetchData(filename) {
+        var att = atts[filename];
+        var path = encodeDocId(doc._id) + '/' + encodeAttachmentId(filename) +
+            '?rev=' + doc._rev;
+        return ourFetch(genDBUrl(host, path)).then(function (response) {
+          if (typeof process !== 'undefined' && !process.browser) {
+            return response.buffer();
+          } else {
+            /* istanbul ignore next */
+            return response.blob();
+          }
+        }).then(function (blob) {
+          if (opts.binary) {
+            // TODO: Can we remove this?
+            if (typeof process !== 'undefined' && !process.browser) {
+              blob.type = att.content_type;
+            }
+            return blob;
+          }
+          return new Promise(function (resolve) {
+            blobToBase64(blob, resolve);
+          });
+        }).then(function (data) {
+          delete att.stub;
+          delete att.length;
+          att.data = data;
+        });
+      }
+
+      var promiseFactories = filenames.map(function (filename) {
+        return function () {
+          return fetchData(filename);
+        };
+      });
+
+      // This limits the number of parallel xhr requests to 5 any time
+      // to avoid issues with maximum browser request limits
+      return pool(promiseFactories, 5);
+    }
+
+    function fetchAllAttachments(docOrDocs) {
+      if (Array.isArray(docOrDocs)) {
+        return Promise.all(docOrDocs.map(function (doc) {
+          if (doc.ok) {
+            return fetchAttachments(doc.ok);
+          }
+        }));
+      }
+      return fetchAttachments(docOrDocs);
+    }
+
+    var url = genDBUrl(host, id + paramsToStr(params));
+    fetchJSON(url).then(function (res) {
+      return Promise.resolve().then(function () {
+        if (opts.attachments) {
+          return fetchAllAttachments(res.data);
+        }
+      }).then(function () {
+        callback(null, res.data);
+      });
+    })["catch"](function (e) {
+      e.docId = id;
+      callback(e);
+    });
+  });
+
+
+  // Delete the document given by doc from the database given by host.
+  api.remove = adapterFun$$1('remove', function (docOrId, optsOrRev, opts, cb) {
+    var doc;
+    if (typeof optsOrRev === 'string') {
+      // id, rev, opts, callback style
+      doc = {
+        _id: docOrId,
+        _rev: optsOrRev
+      };
+      if (typeof opts === 'function') {
+        cb = opts;
+        opts = {};
+      }
+    } else {
+      // doc, opts, callback style
+      doc = docOrId;
+      if (typeof optsOrRev === 'function') {
+        cb = optsOrRev;
+        opts = {};
+      } else {
+        cb = opts;
+        opts = optsOrRev;
+      }
+    }
+
+    var rev$$1 = (doc._rev || opts.rev);
+    var url = genDBUrl(host, encodeDocId(doc._id)) + '?rev=' + rev$$1;
+
+    fetchJSON(url, {method: 'DELETE'}, cb)["catch"](cb);
+  });
+
+  function encodeAttachmentId(attachmentId) {
+    return attachmentId.split("/").map(encodeURIComponent).join("/");
+  }
+
+  // Get the attachment
+  api.getAttachment = adapterFun$$1('getAttachment', function (docId, attachmentId,
+                                                            opts, callback) {
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+    var params = opts.rev ? ('?rev=' + opts.rev) : '';
+    var url = genDBUrl(host, encodeDocId(docId)) + '/' +
+        encodeAttachmentId(attachmentId) + params;
+    var contentType;
+    ourFetch(url, {method: 'GET'}).then(function (response) {
+      contentType = response.headers.get('content-type');
+      if (!response.ok) {
+        throw response;
+      } else {
+        if (typeof process !== 'undefined' && !process.browser) {
+          return response.buffer();
+        } else {
+          /* istanbul ignore next */
+          return response.blob();
+        }
+      }
+    }).then(function (blob) {
+      // TODO: also remove
+      if (typeof process !== 'undefined' && !process.browser) {
+        blob.type = contentType;
+      }
+      callback(null, blob);
+    })["catch"](function (err) {
+      callback(err);
+    });
+  });
+
+  // Remove the attachment given by the id and rev
+  api.removeAttachment =  adapterFun$$1('removeAttachment', function (docId,
+                                                                   attachmentId,
+                                                                   rev$$1,
+                                                                   callback) {
+    var url = genDBUrl(host, encodeDocId(docId) + '/' +
+                       encodeAttachmentId(attachmentId)) + '?rev=' + rev$$1;
+    fetchJSON(url, {method: 'DELETE'}, callback)["catch"](callback);
+  });
+
+  // Add the attachment given by blob and its contentType property
+  // to the document with the given id, the revision given by rev, and
+  // add it to the database given by host.
+  api.putAttachment = adapterFun$$1('putAttachment', function (docId, attachmentId,
+                                                            rev$$1, blob,
+                                                            type, callback) {
+    if (typeof type === 'function') {
+      callback = type;
+      type = blob;
+      blob = rev$$1;
+      rev$$1 = null;
+    }
+    var id = encodeDocId(docId) + '/' + encodeAttachmentId(attachmentId);
+    var url = genDBUrl(host, id);
+    if (rev$$1) {
+      url += '?rev=' + rev$$1;
+    }
+
+    if (typeof blob === 'string') {
+      // input is assumed to be a base64 string
+      var binary;
+      try {
+        binary = thisAtob(blob);
+      } catch (err) {
+        return callback(createError(BAD_ARG,
+                        'Attachment is not a valid base64 string'));
+      }
+      blob = binary ? binStringToBluffer(binary, type) : '';
+    }
+
+    // Add the attachment
+    fetchJSON(url, {
+      headers: new h({'Content-Type': type}),
+      method: 'PUT',
+      body: blob
+    }, callback)["catch"](callback);
+  });
+
+  // Update/create multiple documents given by req in the database
+  // given by host.
+  api._bulkDocs = function (req, opts, callback) {
+    // If new_edits=false then it prevents the database from creating
+    // new revision numbers for the documents. Instead it just uses
+    // the old ones. This is used in database replication.
+    req.new_edits = opts.new_edits;
+
+    setup().then(function () {
+      return Promise.all(req.docs.map(preprocessAttachments$1));
+    }).then(function () {
+      // Update/create the documents
+      return fetchJSON(genDBUrl(host, '_bulk_docs'), {
+        method: 'POST',
+        body: JSON.stringify(req)
+      }, callback);
+    })["catch"](callback);
+  };
+
+
+  // Update/create document
+  api._put = function (doc, opts, callback) {
+    setup().then(function () {
+      return preprocessAttachments$1(doc);
+    }).then(function () {
+      return fetchJSON(genDBUrl(host, encodeDocId(doc._id)), {
+        method: 'PUT',
+        body: JSON.stringify(doc)
+      });
+    }).then(function (result) {
+      callback(null, result.data);
+    })["catch"](function (err) {
+      err.docId = doc && doc._id;
+      callback(err);
+    });
+  };
+
+
+  // Get a listing of the documents in the database given
+  // by host and ordered by increasing id.
+  api.allDocs = adapterFun$$1('allDocs', function (opts, callback) {
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+    opts = clone(opts);
+
+    // List of parameters to add to the GET request
+    var params = {};
+    var body;
+    var method = 'GET';
+
+    if (opts.conflicts) {
+      params.conflicts = true;
+    }
+
+    /* istanbul ignore if */
+    if (opts.update_seq) {
+      params.update_seq = true;
+    }
+
+    if (opts.descending) {
+      params.descending = true;
+    }
+
+    if (opts.include_docs) {
+      params.include_docs = true;
+    }
+
+    // added in CouchDB 1.6.0
+    if (opts.attachments) {
+      params.attachments = true;
+    }
+
+    if (opts.key) {
+      params.key = JSON.stringify(opts.key);
+    }
+
+    if (opts.start_key) {
+      opts.startkey = opts.start_key;
+    }
+
+    if (opts.startkey) {
+      params.startkey = JSON.stringify(opts.startkey);
+    }
+
+    if (opts.end_key) {
+      opts.endkey = opts.end_key;
+    }
+
+    if (opts.endkey) {
+      params.endkey = JSON.stringify(opts.endkey);
+    }
+
+    if (typeof opts.inclusive_end !== 'undefined') {
+      params.inclusive_end = !!opts.inclusive_end;
+    }
+
+    if (typeof opts.limit !== 'undefined') {
+      params.limit = opts.limit;
+    }
+
+    if (typeof opts.skip !== 'undefined') {
+      params.skip = opts.skip;
+    }
+
+    var paramStr = paramsToStr(params);
+
+    if (typeof opts.keys !== 'undefined') {
+      method = 'POST';
+      body = {keys: opts.keys};
+    }
+
+    fetchJSON(genDBUrl(host, '_all_docs' + paramStr), {
+       method: method,
+      body: JSON.stringify(body)
+    }).then(function (result) {
+      if (opts.include_docs && opts.attachments && opts.binary) {
+        result.data.rows.forEach(readAttachmentsAsBlobOrBuffer);
+      }
+      callback(null, result.data);
+    })["catch"](callback);
+  });
+
+  // Get a list of changes made to documents in the database given by host.
+  // TODO According to the README, there should be two other methods here,
+  // api.changes.addListener and api.changes.removeListener.
+  api._changes = function (opts) {
+
+    // We internally page the results of a changes request, this means
+    // if there is a large set of changes to be returned we can start
+    // processing them quicker instead of waiting on the entire
+    // set of changes to return and attempting to process them at once
+    var batchSize = 'batch_size' in opts ? opts.batch_size : CHANGES_BATCH_SIZE;
+
+    opts = clone(opts);
+
+    if (opts.continuous && !('heartbeat' in opts)) {
+      opts.heartbeat = DEFAULT_HEARTBEAT;
+    }
+
+    var requestTimeout = ('timeout' in opts) ? opts.timeout : 30 * 1000;
+
+    // ensure CHANGES_TIMEOUT_BUFFER applies
+    if ('timeout' in opts && opts.timeout &&
+      (requestTimeout - opts.timeout) < CHANGES_TIMEOUT_BUFFER) {
+        requestTimeout = opts.timeout + CHANGES_TIMEOUT_BUFFER;
+    }
+
+    /* istanbul ignore if */
+    if ('heartbeat' in opts && opts.heartbeat &&
+       (requestTimeout - opts.heartbeat) < CHANGES_TIMEOUT_BUFFER) {
+        requestTimeout = opts.heartbeat + CHANGES_TIMEOUT_BUFFER;
+    }
+
+    var params = {};
+    if ('timeout' in opts && opts.timeout) {
+      params.timeout = opts.timeout;
+    }
+
+    var limit = (typeof opts.limit !== 'undefined') ? opts.limit : false;
+    var leftToFetch = limit;
+
+    if (opts.style) {
+      params.style = opts.style;
+    }
+
+    if (opts.include_docs || opts.filter && typeof opts.filter === 'function') {
+      params.include_docs = true;
+    }
+
+    if (opts.attachments) {
+      params.attachments = true;
+    }
+
+    if (opts.continuous) {
+      params.feed = 'longpoll';
+    }
+
+    if (opts.seq_interval) {
+      params.seq_interval = opts.seq_interval;
+    }
+
+    if (opts.conflicts) {
+      params.conflicts = true;
+    }
+
+    if (opts.descending) {
+      params.descending = true;
+    }
+    
+    /* istanbul ignore if */
+    if (opts.update_seq) {
+      params.update_seq = true;
+    }
+
+    if ('heartbeat' in opts) {
+      // If the heartbeat value is false, it disables the default heartbeat
+      if (opts.heartbeat) {
+        params.heartbeat = opts.heartbeat;
+      }
+    }
+
+    if (opts.filter && typeof opts.filter === 'string') {
+      params.filter = opts.filter;
+    }
+
+    if (opts.view && typeof opts.view === 'string') {
+      params.filter = '_view';
+      params.view = opts.view;
+    }
+
+    // If opts.query_params exists, pass it through to the changes request.
+    // These parameters may be used by the filter on the source database.
+    if (opts.query_params && typeof opts.query_params === 'object') {
+      for (var param_name in opts.query_params) {
+        /* istanbul ignore else */
+        if (opts.query_params.hasOwnProperty(param_name)) {
+          params[param_name] = opts.query_params[param_name];
+        }
+      }
+    }
+
+    var method = 'GET';
+    var body;
+
+    if (opts.doc_ids) {
+      // set this automagically for the user; it's annoying that couchdb
+      // requires both a "filter" and a "doc_ids" param.
+      params.filter = '_doc_ids';
+      method = 'POST';
+      body = {doc_ids: opts.doc_ids };
+    }
+    /* istanbul ignore next */
+    else if (opts.selector) {
+      // set this automagically for the user, similar to above
+      params.filter = '_selector';
+      method = 'POST';
+      body = {selector: opts.selector };
+    }
+
+    var controller = new a();
+    var lastFetchedSeq;
+
+    // Get all the changes starting wtih the one immediately after the
+    // sequence number given by since.
+    var fetchData = function (since, callback) {
+      if (opts.aborted) {
+        return;
+      }
+      params.since = since;
+      // "since" can be any kind of json object in Cloudant/CouchDB 2.x
+      /* istanbul ignore next */
+      if (typeof params.since === "object") {
+        params.since = JSON.stringify(params.since);
+      }
+
+      if (opts.descending) {
+        if (limit) {
+          params.limit = leftToFetch;
+        }
+      } else {
+        params.limit = (!limit || leftToFetch > batchSize) ?
+          batchSize : leftToFetch;
+      }
+
+      // Set the options for the ajax call
+      var url = genDBUrl(host, '_changes' + paramsToStr(params));
+      var fetchOpts = {
+        signal: controller.signal,
+        method: method,
+        body: JSON.stringify(body)
+      };
+      lastFetchedSeq = since;
+
+      /* istanbul ignore if */
+      if (opts.aborted) {
+        return;
+      }
+
+      // Get the changes
+      setup().then(function () {
+        return fetchJSON(url, fetchOpts, callback);
+      })["catch"](callback);
+    };
+
+    // If opts.since exists, get all the changes from the sequence
+    // number given by opts.since. Otherwise, get all the changes
+    // from the sequence number 0.
+    var results = {results: []};
+
+    var fetched = function (err, res) {
+      if (opts.aborted) {
+        return;
+      }
+      var raw_results_length = 0;
+      // If the result of the ajax call (res) contains changes (res.results)
+      if (res && res.results) {
+        raw_results_length = res.results.length;
+        results.last_seq = res.last_seq;
+        var pending = null;
+        var lastSeq = null;
+        // Attach 'pending' property if server supports it (CouchDB 2.0+)
+        /* istanbul ignore if */
+        if (typeof res.pending === 'number') {
+          pending = res.pending;
+        }
+        if (typeof results.last_seq === 'string' || typeof results.last_seq === 'number') {
+          lastSeq = results.last_seq;
+        }
+        // For each change
+        var req = {};
+        req.query = opts.query_params;
+        res.results = res.results.filter(function (c) {
+          leftToFetch--;
+          var ret = filterChange(opts)(c);
+          if (ret) {
+            if (opts.include_docs && opts.attachments && opts.binary) {
+              readAttachmentsAsBlobOrBuffer(c);
+            }
+            if (opts.return_docs) {
+              results.results.push(c);
+            }
+            opts.onChange(c, pending, lastSeq);
+          }
+          return ret;
+        });
+      } else if (err) {
+        // In case of an error, stop listening for changes and call
+        // opts.complete
+        opts.aborted = true;
+        opts.complete(err);
+        return;
+      }
+
+      // The changes feed may have timed out with no results
+      // if so reuse last update sequence
+      if (res && res.last_seq) {
+        lastFetchedSeq = res.last_seq;
+      }
+
+      var finished = (limit && leftToFetch <= 0) ||
+        (res && raw_results_length < batchSize) ||
+        (opts.descending);
+
+      if ((opts.continuous && !(limit && leftToFetch <= 0)) || !finished) {
+        // Queue a call to fetch again with the newest sequence number
+        immediate(function () { fetchData(lastFetchedSeq, fetched); });
+      } else {
+        // We're done, call the callback
+        opts.complete(null, results);
+      }
+    };
+
+    fetchData(opts.since || 0, fetched);
+
+    // Return a method to cancel this method from processing any more
+    return {
+      cancel: function () {
+        opts.aborted = true;
+        controller.abort();
+      }
+    };
+  };
+
+  // Given a set of document/revision IDs (given by req), tets the subset of
+  // those that do NOT correspond to revisions stored in the database.
+  // See http://wiki.apache.org/couchdb/HttpPostRevsDiff
+  api.revsDiff = adapterFun$$1('revsDiff', function (req, opts, callback) {
+    // If no options were given, set the callback to be the second parameter
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+
+    // Get the missing document/revision IDs
+    fetchJSON(genDBUrl(host, '_revs_diff'), {
+      method: 'POST',
+      body: JSON.stringify(req)
+    }, callback)["catch"](callback);
+  });
+
+  api._close = function (callback) {
+    callback();
+  };
+
+  api._destroy = function (options, callback) {
+    fetchJSON(genDBUrl(host, ''), {method: 'DELETE'}).then(function (json) {
+      callback(null, json);
+    })["catch"](function (err) {
+      /* istanbul ignore if */
+      if (err.status === 404) {
+        callback(null, {ok: true});
+      } else {
+        callback(err);
+      }
+    });
+  };
+}
+
+// HttpPouch is a valid adapter.
+HttpPouch.valid = function () {
+  return true;
+};
+
+function HttpPouch$1 (PouchDB) {
+  PouchDB.adapter('http', HttpPouch, false);
+  PouchDB.adapter('https', HttpPouch, false);
+}
+
+function QueryParseError(message) {
+  this.status = 400;
+  this.name = 'query_parse_error';
+  this.message = message;
+  this.error = true;
+  try {
+    Error.captureStackTrace(this, QueryParseError);
+  } catch (e) {}
+}
+
+inherits(QueryParseError, Error);
+
+function NotFoundError(message) {
+  this.status = 404;
+  this.name = 'not_found';
+  this.message = message;
+  this.error = true;
+  try {
+    Error.captureStackTrace(this, NotFoundError);
+  } catch (e) {}
+}
+
+inherits(NotFoundError, Error);
+
+function BuiltInError(message) {
+  this.status = 500;
+  this.name = 'invalid_value';
+  this.message = message;
+  this.error = true;
+  try {
+    Error.captureStackTrace(this, BuiltInError);
+  } catch (e) {}
+}
+
+inherits(BuiltInError, Error);
+
+function promisedCallback(promise, callback) {
+  if (callback) {
+    promise.then(function (res) {
+      immediate(function () {
+        callback(null, res);
+      });
+    }, function (reason) {
+      immediate(function () {
+        callback(reason);
+      });
+    });
+  }
+  return promise;
+}
+
+function callbackify(fun) {
+  return getArguments(function (args) {
+    var cb = args.pop();
+    var promise = fun.apply(this, args);
+    if (typeof cb === 'function') {
+      promisedCallback(promise, cb);
+    }
+    return promise;
+  });
+}
+
+// Promise finally util similar to Q.finally
+function fin(promise, finalPromiseFactory) {
+  return promise.then(function (res) {
+    return finalPromiseFactory().then(function () {
+      return res;
+    });
+  }, function (reason) {
+    return finalPromiseFactory().then(function () {
+      throw reason;
+    });
+  });
+}
+
+function sequentialize(queue, promiseFactory) {
+  return function () {
+    var args = arguments;
+    var that = this;
+    return queue.add(function () {
+      return promiseFactory.apply(that, args);
+    });
+  };
+}
+
+// uniq an array of strings, order not guaranteed
+// similar to underscore/lodash _.uniq
+function uniq(arr) {
+  var theSet = new ExportedSet(arr);
+  var result = new Array(theSet.size);
+  var index = -1;
+  theSet.forEach(function (value) {
+    result[++index] = value;
+  });
+  return result;
+}
+
+function mapToKeysArray(map) {
+  var result = new Array(map.size);
+  var index = -1;
+  map.forEach(function (value, key) {
+    result[++index] = key;
+  });
+  return result;
+}
+
+function createBuiltInError(name) {
+  var message = 'builtin ' + name +
+    ' function requires map values to be numbers' +
+    ' or number arrays';
+  return new BuiltInError(message);
+}
+
+function sum(values) {
+  var result = 0;
+  for (var i = 0, len = values.length; i < len; i++) {
+    var num = values[i];
+    if (typeof num !== 'number') {
+      if (Array.isArray(num)) {
+        // lists of numbers are also allowed, sum them separately
+        result = typeof result === 'number' ? [result] : result;
+        for (var j = 0, jLen = num.length; j < jLen; j++) {
+          var jNum = num[j];
+          if (typeof jNum !== 'number') {
+            throw createBuiltInError('_sum');
+          } else if (typeof result[j] === 'undefined') {
+            result.push(jNum);
+          } else {
+            result[j] += jNum;
+          }
+        }
+      } else { // not array/number
+        throw createBuiltInError('_sum');
+      }
+    } else if (typeof result === 'number') {
+      result += num;
+    } else { // add number to array
+      result[0] += num;
+    }
+  }
+  return result;
+}
+
+var log = guardedConsole.bind(null, 'log');
+var isArray = Array.isArray;
+var toJSON = JSON.parse;
+
+function evalFunctionWithEval(func, emit) {
+  return scopeEval(
+    "return (" + func.replace(/;\s*$/, "") + ");",
+    {
+      emit: emit,
+      sum: sum,
+      log: log,
+      isArray: isArray,
+      toJSON: toJSON
+    }
+  );
+}
+
+/*
+ * Simple task queue to sequentialize actions. Assumes
+ * callbacks will eventually fire (once).
+ */
+
+
+function TaskQueue$1() {
+  this.promise = new Promise(function (fulfill) {fulfill(); });
+}
+TaskQueue$1.prototype.add = function (promiseFactory) {
+  this.promise = this.promise["catch"](function () {
+    // just recover
+  }).then(function () {
+    return promiseFactory();
+  });
+  return this.promise;
+};
+TaskQueue$1.prototype.finish = function () {
+  return this.promise;
+};
+
+function stringify(input) {
+  if (!input) {
+    return 'undefined'; // backwards compat for empty reduce
+  }
+  // for backwards compat with mapreduce, functions/strings are stringified
+  // as-is. everything else is JSON-stringified.
+  switch (typeof input) {
+    case 'function':
+      // e.g. a mapreduce map
+      return input.toString();
+    case 'string':
+      // e.g. a mapreduce built-in _reduce function
+      return input.toString();
+    default:
+      // e.g. a JSON object in the case of mango queries
+      return JSON.stringify(input);
+  }
+}
+
+/* create a string signature for a view so we can cache it and uniq it */
+function createViewSignature(mapFun, reduceFun) {
+  // the "undefined" part is for backwards compatibility
+  return stringify(mapFun) + stringify(reduceFun) + 'undefined';
+}
+
+function createView(sourceDB, viewName, mapFun, reduceFun, temporary, localDocName) {
+  var viewSignature = createViewSignature(mapFun, reduceFun);
+
+  var cachedViews;
+  if (!temporary) {
+    // cache this to ensure we don't try to update the same view twice
+    cachedViews = sourceDB._cachedViews = sourceDB._cachedViews || {};
+    if (cachedViews[viewSignature]) {
+      return cachedViews[viewSignature];
+    }
+  }
+
+  var promiseForView = sourceDB.info().then(function (info) {
+
+    var depDbName = info.db_name + '-mrview-' +
+      (temporary ? 'temp' : stringMd5(viewSignature));
+
+    // save the view name in the source db so it can be cleaned up if necessary
+    // (e.g. when the _design doc is deleted, remove all associated view data)
+    function diffFunction(doc) {
+      doc.views = doc.views || {};
+      var fullViewName = viewName;
+      if (fullViewName.indexOf('/') === -1) {
+        fullViewName = viewName + '/' + viewName;
+      }
+      var depDbs = doc.views[fullViewName] = doc.views[fullViewName] || {};
+      /* istanbul ignore if */
+      if (depDbs[depDbName]) {
+        return; // no update necessary
+      }
+      depDbs[depDbName] = true;
+      return doc;
+    }
+    return upsert(sourceDB, '_local/' + localDocName, diffFunction).then(function () {
+      return sourceDB.registerDependentDatabase(depDbName).then(function (res) {
+        var db = res.db;
+        db.auto_compaction = true;
+        var view = {
+          name: depDbName,
+          db: db,
+          sourceDB: sourceDB,
+          adapter: sourceDB.adapter,
+          mapFun: mapFun,
+          reduceFun: reduceFun
+        };
+        return view.db.get('_local/lastSeq')["catch"](function (err) {
+          /* istanbul ignore if */
+          if (err.status !== 404) {
+            throw err;
+          }
+        }).then(function (lastSeqDoc) {
+          view.seq = lastSeqDoc ? lastSeqDoc.seq : 0;
+          if (cachedViews) {
+            view.db.once('destroyed', function () {
+              delete cachedViews[viewSignature];
+            });
+          }
+          return view;
+        });
+      });
+    });
+  });
+
+  if (cachedViews) {
+    cachedViews[viewSignature] = promiseForView;
+  }
+  return promiseForView;
+}
+
+var persistentQueues = {};
+var tempViewQueue = new TaskQueue$1();
+var CHANGES_BATCH_SIZE$1 = 50;
+
+function parseViewName(name) {
+  // can be either 'ddocname/viewname' or just 'viewname'
+  // (where the ddoc name is the same)
+  return name.indexOf('/') === -1 ? [name, name] : name.split('/');
+}
+
+function isGenOne(changes) {
+  // only return true if the current change is 1-
+  // and there are no other leafs
+  return changes.length === 1 && /^1-/.test(changes[0].rev);
+}
+
+function emitError(db, e) {
+  try {
+    db.emit('error', e);
+  } catch (err) {
+    guardedConsole('error',
+      'The user\'s map/reduce function threw an uncaught error.\n' +
+      'You can debug this error by doing:\n' +
+      'myDatabase.on(\'error\', function (err) { debugger; });\n' +
+      'Please double-check your map/reduce function.');
+    guardedConsole('error', e);
+  }
+}
+
+/**
+ * Returns an "abstract" mapreduce object of the form:
+ *
+ *   {
+ *     query: queryFun,
+ *     viewCleanup: viewCleanupFun
+ *   }
+ *
+ * Arguments are:
+ *
+ * localDoc: string
+ *   This is for the local doc that gets saved in order to track the
+ *   "dependent" DBs and clean them up for viewCleanup. It should be
+ *   unique, so that indexer plugins don't collide with each other.
+ * mapper: function (mapFunDef, emit)
+ *   Returns a map function based on the mapFunDef, which in the case of
+ *   normal map/reduce is just the de-stringified function, but may be
+ *   something else, such as an object in the case of pouchdb-find.
+ * reducer: function (reduceFunDef)
+ *   Ditto, but for reducing. Modules don't have to support reducing
+ *   (e.g. pouchdb-find).
+ * ddocValidator: function (ddoc, viewName)
+ *   Throws an error if the ddoc or viewName is not valid.
+ *   This could be a way to communicate to the user that the configuration for the
+ *   indexer is invalid.
+ */
+function createAbstractMapReduce(localDocName, mapper, reducer, ddocValidator) {
+
+  function tryMap(db, fun, doc) {
+    // emit an event if there was an error thrown by a map function.
+    // putting try/catches in a single function also avoids deoptimizations.
+    try {
+      fun(doc);
+    } catch (e) {
+      emitError(db, e);
+    }
+  }
+
+  function tryReduce(db, fun, keys, values, rereduce) {
+    // same as above, but returning the result or an error. there are two separate
+    // functions to avoid extra memory allocations since the tryCode() case is used
+    // for custom map functions (common) vs this function, which is only used for
+    // custom reduce functions (rare)
+    try {
+      return {output : fun(keys, values, rereduce)};
+    } catch (e) {
+      emitError(db, e);
+      return {error: e};
+    }
+  }
+
+  function sortByKeyThenValue(x, y) {
+    var keyCompare = collate(x.key, y.key);
+    return keyCompare !== 0 ? keyCompare : collate(x.value, y.value);
+  }
+
+  function sliceResults(results, limit, skip) {
+    skip = skip || 0;
+    if (typeof limit === 'number') {
+      return results.slice(skip, limit + skip);
+    } else if (skip > 0) {
+      return results.slice(skip);
+    }
+    return results;
+  }
+
+  function rowToDocId(row) {
+    var val = row.value;
+    // Users can explicitly specify a joined doc _id, or it
+    // defaults to the doc _id that emitted the key/value.
+    var docId = (val && typeof val === 'object' && val._id) || row.id;
+    return docId;
+  }
+
+  function readAttachmentsAsBlobOrBuffer(res) {
+    res.rows.forEach(function (row) {
+      var atts = row.doc && row.doc._attachments;
+      if (!atts) {
+        return;
+      }
+      Object.keys(atts).forEach(function (filename) {
+        var att = atts[filename];
+        atts[filename].data = b64ToBluffer(att.data, att.content_type);
+      });
+    });
+  }
+
+  function postprocessAttachments(opts) {
+    return function (res) {
+      if (opts.include_docs && opts.attachments && opts.binary) {
+        readAttachmentsAsBlobOrBuffer(res);
+      }
+      return res;
+    };
+  }
+
+  function addHttpParam(paramName, opts, params, asJson) {
+    // add an http param from opts to params, optionally json-encoded
+    var val = opts[paramName];
+    if (typeof val !== 'undefined') {
+      if (asJson) {
+        val = encodeURIComponent(JSON.stringify(val));
+      }
+      params.push(paramName + '=' + val);
+    }
+  }
+
+  function coerceInteger(integerCandidate) {
+    if (typeof integerCandidate !== 'undefined') {
+      var asNumber = Number(integerCandidate);
+      // prevents e.g. '1foo' or '1.1' being coerced to 1
+      if (!isNaN(asNumber) && asNumber === parseInt(integerCandidate, 10)) {
+        return asNumber;
+      } else {
+        return integerCandidate;
+      }
+    }
+  }
+
+  function coerceOptions(opts) {
+    opts.group_level = coerceInteger(opts.group_level);
+    opts.limit = coerceInteger(opts.limit);
+    opts.skip = coerceInteger(opts.skip);
+    return opts;
+  }
+
+  function checkPositiveInteger(number) {
+    if (number) {
+      if (typeof number !== 'number') {
+        return  new QueryParseError('Invalid value for integer: "' +
+          number + '"');
+      }
+      if (number < 0) {
+        return new QueryParseError('Invalid value for positive integer: ' +
+          '"' + number + '"');
+      }
+    }
+  }
+
+  function checkQueryParseError(options, fun) {
+    var startkeyName = options.descending ? 'endkey' : 'startkey';
+    var endkeyName = options.descending ? 'startkey' : 'endkey';
+
+    if (typeof options[startkeyName] !== 'undefined' &&
+      typeof options[endkeyName] !== 'undefined' &&
+      collate(options[startkeyName], options[endkeyName]) > 0) {
+      throw new QueryParseError('No rows can match your key range, ' +
+        'reverse your start_key and end_key or set {descending : true}');
+    } else if (fun.reduce && options.reduce !== false) {
+      if (options.include_docs) {
+        throw new QueryParseError('{include_docs:true} is invalid for reduce');
+      } else if (options.keys && options.keys.length > 1 &&
+        !options.group && !options.group_level) {
+        throw new QueryParseError('Multi-key fetches for reduce views must use ' +
+          '{group: true}');
+      }
+    }
+    ['group_level', 'limit', 'skip'].forEach(function (optionName) {
+      var error = checkPositiveInteger(options[optionName]);
+      if (error) {
+        throw error;
+      }
+    });
+  }
+
+  function httpQuery(db, fun, opts) {
+    // List of parameters to add to the PUT request
+    var params = [];
+    var body;
+    var method = 'GET';
+    var ok, status;
+
+    // If opts.reduce exists and is defined, then add it to the list
+    // of parameters.
+    // If reduce=false then the results are that of only the map function
+    // not the final result of map and reduce.
+    addHttpParam('reduce', opts, params);
+    addHttpParam('include_docs', opts, params);
+    addHttpParam('attachments', opts, params);
+    addHttpParam('limit', opts, params);
+    addHttpParam('descending', opts, params);
+    addHttpParam('group', opts, params);
+    addHttpParam('group_level', opts, params);
+    addHttpParam('skip', opts, params);
+    addHttpParam('stale', opts, params);
+    addHttpParam('conflicts', opts, params);
+    addHttpParam('startkey', opts, params, true);
+    addHttpParam('start_key', opts, params, true);
+    addHttpParam('endkey', opts, params, true);
+    addHttpParam('end_key', opts, params, true);
+    addHttpParam('inclusive_end', opts, params);
+    addHttpParam('key', opts, params, true);
+    addHttpParam('update_seq', opts, params);
+
+    // Format the list of parameters into a valid URI query string
+    params = params.join('&');
+    params = params === '' ? '' : '?' + params;
+
+    // If keys are supplied, issue a POST to circumvent GET query string limits
+    // see http://wiki.apache.org/couchdb/HTTP_view_API#Querying_Options
+    if (typeof opts.keys !== 'undefined') {
+      var MAX_URL_LENGTH = 2000;
+      // according to http://stackoverflow.com/a/417184/680742,
+      // the de facto URL length limit is 2000 characters
+
+      var keysAsString =
+        'keys=' + encodeURIComponent(JSON.stringify(opts.keys));
+      if (keysAsString.length + params.length + 1 <= MAX_URL_LENGTH) {
+        // If the keys are short enough, do a GET. we do this to work around
+        // Safari not understanding 304s on POSTs (see pouchdb/pouchdb#1239)
+        params += (params[0] === '?' ? '&' : '?') + keysAsString;
+      } else {
+        method = 'POST';
+        if (typeof fun === 'string') {
+          body = {keys: opts.keys};
+        } else { // fun is {map : mapfun}, so append to this
+          fun.keys = opts.keys;
+        }
+      }
+    }
+
+    // We are referencing a query defined in the design doc
+    if (typeof fun === 'string') {
+      var parts = parseViewName(fun);
+      return db.fetch('_design/' + parts[0] + '/_view/' + parts[1] + params, {
+        headers: new h({'Content-Type': 'application/json'}),
+        method: method,
+        body: JSON.stringify(body)
+      }).then(function (response) {
+        ok = response.ok;
+        status = response.status;
+        return response.json();
+      }).then(function (result) {
+        if (!ok) {
+          result.status = status;
+          throw generateErrorFromResponse(result);
+        }
+        // fail the entire request if the result contains an error
+        result.rows.forEach(function (row) {
+          /* istanbul ignore if */
+          if (row.value && row.value.error && row.value.error === "builtin_reduce_error") {
+            throw new Error(row.reason);
+          }
+        });
+        return result;
+      }).then(postprocessAttachments(opts));
+    }
+
+    // We are using a temporary view, terrible for performance, good for testing
+    body = body || {};
+    Object.keys(fun).forEach(function (key) {
+      if (Array.isArray(fun[key])) {
+        body[key] = fun[key];
+      } else {
+        body[key] = fun[key].toString();
+      }
+    });
+
+    return db.fetch('_temp_view' + params, {
+      headers: new h({'Content-Type': 'application/json'}),
+      method: 'POST',
+      body: JSON.stringify(body)
+    }).then(function (response) {
+        ok = response.ok;
+        status = response.status;
+      return response.json();
+    }).then(function (result) {
+      if (!ok) {
+        result.status = status;
+        throw generateErrorFromResponse(result);
+      }
+      return result;
+    }).then(postprocessAttachments(opts));
+  }
+
+  // custom adapters can define their own api._query
+  // and override the default behavior
+  /* istanbul ignore next */
+  function customQuery(db, fun, opts) {
+    return new Promise(function (resolve, reject) {
+      db._query(fun, opts, function (err, res) {
+        if (err) {
+          return reject(err);
+        }
+        resolve(res);
+      });
+    });
+  }
+
+  // custom adapters can define their own api._viewCleanup
+  // and override the default behavior
+  /* istanbul ignore next */
+  function customViewCleanup(db) {
+    return new Promise(function (resolve, reject) {
+      db._viewCleanup(function (err, res) {
+        if (err) {
+          return reject(err);
+        }
+        resolve(res);
+      });
+    });
+  }
+
+  function defaultsTo(value) {
+    return function (reason) {
+      /* istanbul ignore else */
+      if (reason.status === 404) {
+        return value;
+      } else {
+        throw reason;
+      }
+    };
+  }
+
+  // returns a promise for a list of docs to update, based on the input docId.
+  // the order doesn't matter, because post-3.2.0, bulkDocs
+  // is an atomic operation in all three adapters.
+  function getDocsToPersist(docId, view, docIdsToChangesAndEmits) {
+    var metaDocId = '_local/doc_' + docId;
+    var defaultMetaDoc = {_id: metaDocId, keys: []};
+    var docData = docIdsToChangesAndEmits.get(docId);
+    var indexableKeysToKeyValues = docData[0];
+    var changes = docData[1];
+
+    function getMetaDoc() {
+      if (isGenOne(changes)) {
+        // generation 1, so we can safely assume initial state
+        // for performance reasons (avoids unnecessary GETs)
+        return Promise.resolve(defaultMetaDoc);
+      }
+      return view.db.get(metaDocId)["catch"](defaultsTo(defaultMetaDoc));
+    }
+
+    function getKeyValueDocs(metaDoc) {
+      if (!metaDoc.keys.length) {
+        // no keys, no need for a lookup
+        return Promise.resolve({rows: []});
+      }
+      return view.db.allDocs({
+        keys: metaDoc.keys,
+        include_docs: true
+      });
+    }
+
+    function processKeyValueDocs(metaDoc, kvDocsRes) {
+      var kvDocs = [];
+      var oldKeys = new ExportedSet();
+
+      for (var i = 0, len = kvDocsRes.rows.length; i < len; i++) {
+        var row = kvDocsRes.rows[i];
+        var doc = row.doc;
+        if (!doc) { // deleted
+          continue;
+        }
+        kvDocs.push(doc);
+        oldKeys.add(doc._id);
+        doc._deleted = !indexableKeysToKeyValues.has(doc._id);
+        if (!doc._deleted) {
+          var keyValue = indexableKeysToKeyValues.get(doc._id);
+          if ('value' in keyValue) {
+            doc.value = keyValue.value;
+          }
+        }
+      }
+      var newKeys = mapToKeysArray(indexableKeysToKeyValues);
+      newKeys.forEach(function (key) {
+        if (!oldKeys.has(key)) {
+          // new doc
+          var kvDoc = {
+            _id: key
+          };
+          var keyValue = indexableKeysToKeyValues.get(key);
+          if ('value' in keyValue) {
+            kvDoc.value = keyValue.value;
+          }
+          kvDocs.push(kvDoc);
+        }
+      });
+      metaDoc.keys = uniq(newKeys.concat(metaDoc.keys));
+      kvDocs.push(metaDoc);
+
+      return kvDocs;
+    }
+
+    return getMetaDoc().then(function (metaDoc) {
+      return getKeyValueDocs(metaDoc).then(function (kvDocsRes) {
+        return processKeyValueDocs(metaDoc, kvDocsRes);
+      });
+    });
+  }
+
+  // updates all emitted key/value docs and metaDocs in the mrview database
+  // for the given batch of documents from the source database
+  function saveKeyValues(view, docIdsToChangesAndEmits, seq) {
+    var seqDocId = '_local/lastSeq';
+    return view.db.get(seqDocId)[
+      "catch"](defaultsTo({_id: seqDocId, seq: 0}))
+      .then(function (lastSeqDoc) {
+        var docIds = mapToKeysArray(docIdsToChangesAndEmits);
+        return Promise.all(docIds.map(function (docId) {
+          return getDocsToPersist(docId, view, docIdsToChangesAndEmits);
+        })).then(function (listOfDocsToPersist) {
+          var docsToPersist = flatten(listOfDocsToPersist);
+          lastSeqDoc.seq = seq;
+          docsToPersist.push(lastSeqDoc);
+          // write all docs in a single operation, update the seq once
+          return view.db.bulkDocs({docs : docsToPersist});
+        });
+      });
+  }
+
+  function getQueue(view) {
+    var viewName = typeof view === 'string' ? view : view.name;
+    var queue = persistentQueues[viewName];
+    if (!queue) {
+      queue = persistentQueues[viewName] = new TaskQueue$1();
+    }
+    return queue;
+  }
+
+  function updateView(view) {
+    return sequentialize(getQueue(view), function () {
+      return updateViewInQueue(view);
+    })();
+  }
+
+  function updateViewInQueue(view) {
+    // bind the emit function once
+    var mapResults;
+    var doc;
+
+    function emit(key, value) {
+      var output = {id: doc._id, key: normalizeKey(key)};
+      // Don't explicitly store the value unless it's defined and non-null.
+      // This saves on storage space, because often people don't use it.
+      if (typeof value !== 'undefined' && value !== null) {
+        output.value = normalizeKey(value);
+      }
+      mapResults.push(output);
+    }
+
+    var mapFun = mapper(view.mapFun, emit);
+
+    var currentSeq = view.seq || 0;
+
+    function processChange(docIdsToChangesAndEmits, seq) {
+      return function () {
+        return saveKeyValues(view, docIdsToChangesAndEmits, seq);
+      };
+    }
+
+    var queue = new TaskQueue$1();
+
+    function processNextBatch() {
+      return view.sourceDB.changes({
+        return_docs: true,
+        conflicts: true,
+        include_docs: true,
+        style: 'all_docs',
+        since: currentSeq,
+        limit: CHANGES_BATCH_SIZE$1
+      }).then(processBatch);
+    }
+
+    function processBatch(response) {
+      var results = response.results;
+      if (!results.length) {
+        return;
+      }
+      var docIdsToChangesAndEmits = createDocIdsToChangesAndEmits(results);
+      queue.add(processChange(docIdsToChangesAndEmits, currentSeq));
+      if (results.length < CHANGES_BATCH_SIZE$1) {
+        return;
+      }
+      return processNextBatch();
+    }
+
+    function createDocIdsToChangesAndEmits(results) {
+      var docIdsToChangesAndEmits = new ExportedMap();
+      for (var i = 0, len = results.length; i < len; i++) {
+        var change = results[i];
+        if (change.doc._id[0] !== '_') {
+          mapResults = [];
+          doc = change.doc;
+
+          if (!doc._deleted) {
+            tryMap(view.sourceDB, mapFun, doc);
+          }
+          mapResults.sort(sortByKeyThenValue);
+
+          var indexableKeysToKeyValues = createIndexableKeysToKeyValues(mapResults);
+          docIdsToChangesAndEmits.set(change.doc._id, [
+            indexableKeysToKeyValues,
+            change.changes
+          ]);
+        }
+        currentSeq = change.seq;
+      }
+      return docIdsToChangesAndEmits;
+    }
+
+    function createIndexableKeysToKeyValues(mapResults) {
+      var indexableKeysToKeyValues = new ExportedMap();
+      var lastKey;
+      for (var i = 0, len = mapResults.length; i < len; i++) {
+        var emittedKeyValue = mapResults[i];
+        var complexKey = [emittedKeyValue.key, emittedKeyValue.id];
+        if (i > 0 && collate(emittedKeyValue.key, lastKey) === 0) {
+          complexKey.push(i); // dup key+id, so make it unique
+        }
+        indexableKeysToKeyValues.set(toIndexableString(complexKey), emittedKeyValue);
+        lastKey = emittedKeyValue.key;
+      }
+      return indexableKeysToKeyValues;
+    }
+
+    return processNextBatch().then(function () {
+      return queue.finish();
+    }).then(function () {
+      view.seq = currentSeq;
+    });
+  }
+
+  function reduceView(view, results, options) {
+    if (options.group_level === 0) {
+      delete options.group_level;
+    }
+
+    var shouldGroup = options.group || options.group_level;
+
+    var reduceFun = reducer(view.reduceFun);
+
+    var groups = [];
+    var lvl = isNaN(options.group_level) ? Number.POSITIVE_INFINITY :
+      options.group_level;
+    results.forEach(function (e) {
+      var last = groups[groups.length - 1];
+      var groupKey = shouldGroup ? e.key : null;
+
+      // only set group_level for array keys
+      if (shouldGroup && Array.isArray(groupKey)) {
+        groupKey = groupKey.slice(0, lvl);
+      }
+
+      if (last && collate(last.groupKey, groupKey) === 0) {
+        last.keys.push([e.key, e.id]);
+        last.values.push(e.value);
+        return;
+      }
+      groups.push({
+        keys: [[e.key, e.id]],
+        values: [e.value],
+        groupKey: groupKey
+      });
+    });
+    results = [];
+    for (var i = 0, len = groups.length; i < len; i++) {
+      var e = groups[i];
+      var reduceTry = tryReduce(view.sourceDB, reduceFun, e.keys, e.values, false);
+      if (reduceTry.error && reduceTry.error instanceof BuiltInError) {
+        // CouchDB returns an error if a built-in errors out
+        throw reduceTry.error;
+      }
+      results.push({
+        // CouchDB just sets the value to null if a non-built-in errors out
+        value: reduceTry.error ? null : reduceTry.output,
+        key: e.groupKey
+      });
+    }
+    // no total_rows/offset when reducing
+    return {rows: sliceResults(results, options.limit, options.skip)};
+  }
+
+  function queryView(view, opts) {
+    return sequentialize(getQueue(view), function () {
+      return queryViewInQueue(view, opts);
+    })();
+  }
+
+  function queryViewInQueue(view, opts) {
+    var totalRows;
+    var shouldReduce = view.reduceFun && opts.reduce !== false;
+    var skip = opts.skip || 0;
+    if (typeof opts.keys !== 'undefined' && !opts.keys.length) {
+      // equivalent query
+      opts.limit = 0;
+      delete opts.keys;
+    }
+
+    function fetchFromView(viewOpts) {
+      viewOpts.include_docs = true;
+      return view.db.allDocs(viewOpts).then(function (res) {
+        totalRows = res.total_rows;
+        return res.rows.map(function (result) {
+
+          // implicit migration - in older versions of PouchDB,
+          // we explicitly stored the doc as {id: ..., key: ..., value: ...}
+          // this is tested in a migration test
+          /* istanbul ignore next */
+          if ('value' in result.doc && typeof result.doc.value === 'object' &&
+            result.doc.value !== null) {
+            var keys = Object.keys(result.doc.value).sort();
+            // this detection method is not perfect, but it's unlikely the user
+            // emitted a value which was an object with these 3 exact keys
+            var expectedKeys = ['id', 'key', 'value'];
+            if (!(keys < expectedKeys || keys > expectedKeys)) {
+              return result.doc.value;
+            }
+          }
+
+          var parsedKeyAndDocId = parseIndexableString(result.doc._id);
+          return {
+            key: parsedKeyAndDocId[0],
+            id: parsedKeyAndDocId[1],
+            value: ('value' in result.doc ? result.doc.value : null)
+          };
+        });
+      });
+    }
+
+    function onMapResultsReady(rows) {
+      var finalResults;
+      if (shouldReduce) {
+        finalResults = reduceView(view, rows, opts);
+      } else {
+        finalResults = {
+          total_rows: totalRows,
+          offset: skip,
+          rows: rows
+        };
+      }
+      /* istanbul ignore if */
+      if (opts.update_seq) {
+        finalResults.update_seq = view.seq;
+      }
+      if (opts.include_docs) {
+        var docIds = uniq(rows.map(rowToDocId));
+
+        return view.sourceDB.allDocs({
+          keys: docIds,
+          include_docs: true,
+          conflicts: opts.conflicts,
+          attachments: opts.attachments,
+          binary: opts.binary
+        }).then(function (allDocsRes) {
+          var docIdsToDocs = new ExportedMap();
+          allDocsRes.rows.forEach(function (row) {
+            docIdsToDocs.set(row.id, row.doc);
+          });
+          rows.forEach(function (row) {
+            var docId = rowToDocId(row);
+            var doc = docIdsToDocs.get(docId);
+            if (doc) {
+              row.doc = doc;
+            }
+          });
+          return finalResults;
+        });
+      } else {
+        return finalResults;
+      }
+    }
+
+    if (typeof opts.keys !== 'undefined') {
+      var keys = opts.keys;
+      var fetchPromises = keys.map(function (key) {
+        var viewOpts = {
+          startkey : toIndexableString([key]),
+          endkey   : toIndexableString([key, {}])
+        };
+        /* istanbul ignore if */
+        if (opts.update_seq) {
+          viewOpts.update_seq = true;
+        }
+        return fetchFromView(viewOpts);
+      });
+      return Promise.all(fetchPromises).then(flatten).then(onMapResultsReady);
+    } else { // normal query, no 'keys'
+      var viewOpts = {
+        descending : opts.descending
+      };
+      /* istanbul ignore if */
+      if (opts.update_seq) {
+        viewOpts.update_seq = true;
+      }
+      var startkey;
+      var endkey;
+      if ('start_key' in opts) {
+        startkey = opts.start_key;
+      }
+      if ('startkey' in opts) {
+        startkey = opts.startkey;
+      }
+      if ('end_key' in opts) {
+        endkey = opts.end_key;
+      }
+      if ('endkey' in opts) {
+        endkey = opts.endkey;
+      }
+      if (typeof startkey !== 'undefined') {
+        viewOpts.startkey = opts.descending ?
+          toIndexableString([startkey, {}]) :
+          toIndexableString([startkey]);
+      }
+      if (typeof endkey !== 'undefined') {
+        var inclusiveEnd = opts.inclusive_end !== false;
+        if (opts.descending) {
+          inclusiveEnd = !inclusiveEnd;
+        }
+
+        viewOpts.endkey = toIndexableString(
+          inclusiveEnd ? [endkey, {}] : [endkey]);
+      }
+      if (typeof opts.key !== 'undefined') {
+        var keyStart = toIndexableString([opts.key]);
+        var keyEnd = toIndexableString([opts.key, {}]);
+        if (viewOpts.descending) {
+          viewOpts.endkey = keyStart;
+          viewOpts.startkey = keyEnd;
+        } else {
+          viewOpts.startkey = keyStart;
+          viewOpts.endkey = keyEnd;
+        }
+      }
+      if (!shouldReduce) {
+        if (typeof opts.limit === 'number') {
+          viewOpts.limit = opts.limit;
+        }
+        viewOpts.skip = skip;
+      }
+      return fetchFromView(viewOpts).then(onMapResultsReady);
+    }
+  }
+
+  function httpViewCleanup(db) {
+    return db.fetch('_view_cleanup', {
+      headers: new h({'Content-Type': 'application/json'}),
+      method: 'POST'
+    }).then(function (response) {
+      return response.json();
+    });
+  }
+
+  function localViewCleanup(db) {
+    return db.get('_local/' + localDocName).then(function (metaDoc) {
+      var docsToViews = new ExportedMap();
+      Object.keys(metaDoc.views).forEach(function (fullViewName) {
+        var parts = parseViewName(fullViewName);
+        var designDocName = '_design/' + parts[0];
+        var viewName = parts[1];
+        var views = docsToViews.get(designDocName);
+        if (!views) {
+          views = new ExportedSet();
+          docsToViews.set(designDocName, views);
+        }
+        views.add(viewName);
+      });
+      var opts = {
+        keys : mapToKeysArray(docsToViews),
+        include_docs : true
+      };
+      return db.allDocs(opts).then(function (res) {
+        var viewsToStatus = {};
+        res.rows.forEach(function (row) {
+          var ddocName = row.key.substring(8); // cuts off '_design/'
+          docsToViews.get(row.key).forEach(function (viewName) {
+            var fullViewName = ddocName + '/' + viewName;
+            /* istanbul ignore if */
+            if (!metaDoc.views[fullViewName]) {
+              // new format, without slashes, to support PouchDB 2.2.0
+              // migration test in pouchdb's browser.migration.js verifies this
+              fullViewName = viewName;
+            }
+            var viewDBNames = Object.keys(metaDoc.views[fullViewName]);
+            // design doc deleted, or view function nonexistent
+            var statusIsGood = row.doc && row.doc.views &&
+              row.doc.views[viewName];
+            viewDBNames.forEach(function (viewDBName) {
+              viewsToStatus[viewDBName] =
+                viewsToStatus[viewDBName] || statusIsGood;
+            });
+          });
+        });
+        var dbsToDelete = Object.keys(viewsToStatus).filter(
+          function (viewDBName) { return !viewsToStatus[viewDBName]; });
+        var destroyPromises = dbsToDelete.map(function (viewDBName) {
+          return sequentialize(getQueue(viewDBName), function () {
+            return new db.constructor(viewDBName, db.__opts).destroy();
+          })();
+        });
+        return Promise.all(destroyPromises).then(function () {
+          return {ok: true};
+        });
+      });
+    }, defaultsTo({ok: true}));
+  }
+
+  function queryPromised(db, fun, opts) {
+    /* istanbul ignore next */
+    if (typeof db._query === 'function') {
+      return customQuery(db, fun, opts);
+    }
+    if (isRemote(db)) {
+      return httpQuery(db, fun, opts);
+    }
+
+    if (typeof fun !== 'string') {
+      // temp_view
+      checkQueryParseError(opts, fun);
+
+      tempViewQueue.add(function () {
+        var createViewPromise = createView(
+          /* sourceDB */ db,
+          /* viewName */ 'temp_view/temp_view',
+          /* mapFun */ fun.map,
+          /* reduceFun */ fun.reduce,
+          /* temporary */ true,
+          /* localDocName */ localDocName);
+        return createViewPromise.then(function (view) {
+          return fin(updateView(view).then(function () {
+            return queryView(view, opts);
+          }), function () {
+            return view.db.destroy();
+          });
+        });
+      });
+      return tempViewQueue.finish();
+    } else {
+      // persistent view
+      var fullViewName = fun;
+      var parts = parseViewName(fullViewName);
+      var designDocName = parts[0];
+      var viewName = parts[1];
+      return db.get('_design/' + designDocName).then(function (doc) {
+        var fun = doc.views && doc.views[viewName];
+
+        if (!fun) {
+          // basic validator; it's assumed that every subclass would want this
+          throw new NotFoundError('ddoc ' + doc._id + ' has no view named ' +
+            viewName);
+        }
+
+        ddocValidator(doc, viewName);
+        checkQueryParseError(opts, fun);
+
+        var createViewPromise = createView(
+          /* sourceDB */ db,
+          /* viewName */ fullViewName,
+          /* mapFun */ fun.map,
+          /* reduceFun */ fun.reduce,
+          /* temporary */ false,
+          /* localDocName */ localDocName);
+        return createViewPromise.then(function (view) {
+          if (opts.stale === 'ok' || opts.stale === 'update_after') {
+            if (opts.stale === 'update_after') {
+              immediate(function () {
+                updateView(view);
+              });
+            }
+            return queryView(view, opts);
+          } else { // stale not ok
+            return updateView(view).then(function () {
+              return queryView(view, opts);
+            });
+          }
+        });
+      });
+    }
+  }
+
+  function abstractQuery(fun, opts, callback) {
+    var db = this;
+    if (typeof opts === 'function') {
+      callback = opts;
+      opts = {};
+    }
+    opts = opts ? coerceOptions(opts) : {};
+
+    if (typeof fun === 'function') {
+      fun = {map : fun};
+    }
+
+    var promise = Promise.resolve().then(function () {
+      return queryPromised(db, fun, opts);
+    });
+    promisedCallback(promise, callback);
+    return promise;
+  }
+
+  var abstractViewCleanup = callbackify(function () {
+    var db = this;
+    /* istanbul ignore next */
+    if (typeof db._viewCleanup === 'function') {
+      return customViewCleanup(db);
+    }
+    if (isRemote(db)) {
+      return httpViewCleanup(db);
+    }
+    return localViewCleanup(db);
+  });
+
+  return {
+    query: abstractQuery,
+    viewCleanup: abstractViewCleanup
+  };
+}
+
+var builtInReduce = {
+  _sum: function (keys, values) {
+    return sum(values);
+  },
+
+  _count: function (keys, values) {
+    return values.length;
+  },
+
+  _stats: function (keys, values) {
+    // no need to implement rereduce=true, because Pouch
+    // will never call it
+    function sumsqr(values) {
+      var _sumsqr = 0;
+      for (var i = 0, len = values.length; i < len; i++) {
+        var num = values[i];
+        _sumsqr += (num * num);
+      }
+      return _sumsqr;
+    }
+    return {
+      sum     : sum(values),
+      min     : Math.min.apply(null, values),
+      max     : Math.max.apply(null, values),
+      count   : values.length,
+      sumsqr : sumsqr(values)
+    };
+  }
+};
+
+function getBuiltIn(reduceFunString) {
+  if (/^_sum/.test(reduceFunString)) {
+    return builtInReduce._sum;
+  } else if (/^_count/.test(reduceFunString)) {
+    return builtInReduce._count;
+  } else if (/^_stats/.test(reduceFunString)) {
+    return builtInReduce._stats;
+  } else if (/^_/.test(reduceFunString)) {
+    throw new Error(reduceFunString + ' is not a supported reduce function.');
+  }
+}
+
+function mapper(mapFun, emit) {
+  // for temp_views one can use emit(doc, emit), see #38
+  if (typeof mapFun === "function" && mapFun.length === 2) {
+    var origMap = mapFun;
+    return function (doc) {
+      return origMap(doc, emit);
+    };
+  } else {
+    return evalFunctionWithEval(mapFun.toString(), emit);
+  }
+}
+
+function reducer(reduceFun) {
+  var reduceFunString = reduceFun.toString();
+  var builtIn = getBuiltIn(reduceFunString);
+  if (builtIn) {
+    return builtIn;
+  } else {
+    return evalFunctionWithEval(reduceFunString);
+  }
+}
+
+function ddocValidator(ddoc, viewName) {
+  var fun = ddoc.views && ddoc.views[viewName];
+  if (typeof fun.map !== 'string') {
+    throw new NotFoundError('ddoc ' + ddoc._id + ' has no string view named ' +
+      viewName + ', instead found object of type: ' + typeof fun.map);
+  }
+}
+
+var localDocName = 'mrviews';
+var abstract = createAbstractMapReduce(localDocName, mapper, reducer, ddocValidator);
+
+function query(fun, opts, callback) {
+  return abstract.query.call(this, fun, opts, callback);
+}
+
+function viewCleanup(callback) {
+  return abstract.viewCleanup.call(this, callback);
+}
+
+var mapreduce = {
+  query: query,
+  viewCleanup: viewCleanup
+};
+
+function isGenOne$1(rev$$1) {
+  return /^1-/.test(rev$$1);
+}
+
+function fileHasChanged(localDoc, remoteDoc, filename) {
+  return !localDoc._attachments ||
+         !localDoc._attachments[filename] ||
+         localDoc._attachments[filename].digest !== remoteDoc._attachments[filename].digest;
+}
+
+function getDocAttachments(db, doc) {
+  var filenames = Object.keys(doc._attachments);
+  return Promise.all(filenames.map(function (filename) {
+    return db.getAttachment(doc._id, filename, {rev: doc._rev});
+  }));
+}
+
+function getDocAttachmentsFromTargetOrSource(target, src, doc) {
+  var doCheckForLocalAttachments = isRemote(src) && !isRemote(target);
+  var filenames = Object.keys(doc._attachments);
+
+  if (!doCheckForLocalAttachments) {
+    return getDocAttachments(src, doc);
+  }
+
+  return target.get(doc._id).then(function (localDoc) {
+    return Promise.all(filenames.map(function (filename) {
+      if (fileHasChanged(localDoc, doc, filename)) {
+        return src.getAttachment(doc._id, filename);
+      }
+
+      return target.getAttachment(localDoc._id, filename);
+    }));
+  })["catch"](function (error) {
+    /* istanbul ignore if */
+    if (error.status !== 404) {
+      throw error;
+    }
+
+    return getDocAttachments(src, doc);
+  });
+}
+
+function createBulkGetOpts(diffs) {
+  var requests = [];
+  Object.keys(diffs).forEach(function (id) {
+    var missingRevs = diffs[id].missing;
+    missingRevs.forEach(function (missingRev) {
+      requests.push({
+        id: id,
+        rev: missingRev
+      });
+    });
+  });
+
+  return {
+    docs: requests,
+    revs: true,
+    latest: true
+  };
+}
+
+//
+// Fetch all the documents from the src as described in the "diffs",
+// which is a mapping of docs IDs to revisions. If the state ever
+// changes to "cancelled", then the returned promise will be rejected.
+// Else it will be resolved with a list of fetched documents.
+//
+function getDocs(src, target, diffs, state) {
+  diffs = clone(diffs); // we do not need to modify this
+
+  var resultDocs = [],
+      ok = true;
+
+  function getAllDocs() {
+
+    var bulkGetOpts = createBulkGetOpts(diffs);
+
+    if (!bulkGetOpts.docs.length) { // optimization: skip empty requests
+      return;
+    }
+
+    return src.bulkGet(bulkGetOpts).then(function (bulkGetResponse) {
+      /* istanbul ignore if */
+      if (state.cancelled) {
+        throw new Error('cancelled');
+      }
+      return Promise.all(bulkGetResponse.results.map(function (bulkGetInfo) {
+        return Promise.all(bulkGetInfo.docs.map(function (doc) {
+          var remoteDoc = doc.ok;
+
+          if (doc.error) {
+            // when AUTO_COMPACTION is set, docs can be returned which look
+            // like this: {"missing":"1-7c3ac256b693c462af8442f992b83696"}
+            ok = false;
+          }
+
+          if (!remoteDoc || !remoteDoc._attachments) {
+            return remoteDoc;
+          }
+
+          return getDocAttachmentsFromTargetOrSource(target, src, remoteDoc)
+                   .then(function (attachments) {
+                           var filenames = Object.keys(remoteDoc._attachments);
+                           attachments
+                             .forEach(function (attachment, i) {
+                                        var att = remoteDoc._attachments[filenames[i]];
+                                        delete att.stub;
+                                        delete att.length;
+                                        att.data = attachment;
+                                      });
+
+                                      return remoteDoc;
+                                    });
+        }));
+      }))
+
+      .then(function (results) {
+        resultDocs = resultDocs.concat(flatten(results).filter(Boolean));
+      });
+    });
+  }
+
+  function hasAttachments(doc) {
+    return doc._attachments && Object.keys(doc._attachments).length > 0;
+  }
+
+  function hasConflicts(doc) {
+    return doc._conflicts && doc._conflicts.length > 0;
+  }
+
+  function fetchRevisionOneDocs(ids) {
+    // Optimization: fetch gen-1 docs and attachments in
+    // a single request using _all_docs
+    return src.allDocs({
+      keys: ids,
+      include_docs: true,
+      conflicts: true
+    }).then(function (res) {
+      if (state.cancelled) {
+        throw new Error('cancelled');
+      }
+      res.rows.forEach(function (row) {
+        if (row.deleted || !row.doc || !isGenOne$1(row.value.rev) ||
+            hasAttachments(row.doc) || hasConflicts(row.doc)) {
+          // if any of these conditions apply, we need to fetch using get()
+          return;
+        }
+
+        // strip _conflicts array to appease CSG (#5793)
+        /* istanbul ignore if */
+        if (row.doc._conflicts) {
+          delete row.doc._conflicts;
+        }
+
+        // the doc we got back from allDocs() is sufficient
+        resultDocs.push(row.doc);
+        delete diffs[row.id];
+      });
+    });
+  }
+
+  function getRevisionOneDocs() {
+    // filter out the generation 1 docs and get them
+    // leaving the non-generation one docs to be got otherwise
+    var ids = Object.keys(diffs).filter(function (id) {
+      var missing = diffs[id].missing;
+      return missing.length === 1 && isGenOne$1(missing[0]);
+    });
+    if (ids.length > 0) {
+      return fetchRevisionOneDocs(ids);
+    }
+  }
+
+  function returnResult() {
+    return { ok:ok, docs:resultDocs };
+  }
+
+  return Promise.resolve()
+    .then(getRevisionOneDocs)
+    .then(getAllDocs)
+    .then(returnResult);
+}
+
+var CHECKPOINT_VERSION = 1;
+var REPLICATOR = "pouchdb";
+// This is an arbitrary number to limit the
+// amount of replication history we save in the checkpoint.
+// If we save too much, the checkpoing docs will become very big,
+// if we save fewer, we'll run a greater risk of having to
+// read all the changes from 0 when checkpoint PUTs fail
+// CouchDB 2.0 has a more involved history pruning,
+// but let's go for the simple version for now.
+var CHECKPOINT_HISTORY_SIZE = 5;
+var LOWEST_SEQ = 0;
+
+function updateCheckpoint(db, id, checkpoint, session, returnValue) {
+  return db.get(id)["catch"](function (err) {
+    if (err.status === 404) {
+      if (db.adapter === 'http' || db.adapter === 'https') {
+        explainError(
+          404, 'PouchDB is just checking if a remote checkpoint exists.'
+        );
+      }
+      return {
+        session_id: session,
+        _id: id,
+        history: [],
+        replicator: REPLICATOR,
+        version: CHECKPOINT_VERSION
+      };
+    }
+    throw err;
+  }).then(function (doc) {
+    if (returnValue.cancelled) {
+      return;
+    }
+
+    // if the checkpoint has not changed, do not update
+    if (doc.last_seq === checkpoint) {
+      return;
+    }
+
+    // Filter out current entry for this replication
+    doc.history = (doc.history || []).filter(function (item) {
+      return item.session_id !== session;
+    });
+
+    // Add the latest checkpoint to history
+    doc.history.unshift({
+      last_seq: checkpoint,
+      session_id: session
+    });
+
+    // Just take the last pieces in history, to
+    // avoid really big checkpoint docs.
+    // see comment on history size above
+    doc.history = doc.history.slice(0, CHECKPOINT_HISTORY_SIZE);
+
+    doc.version = CHECKPOINT_VERSION;
+    doc.replicator = REPLICATOR;
+
+    doc.session_id = session;
+    doc.last_seq = checkpoint;
+
+    return db.put(doc)["catch"](function (err) {
+      if (err.status === 409) {
+        // retry; someone is trying to write a checkpoint simultaneously
+        return updateCheckpoint(db, id, checkpoint, session, returnValue);
+      }
+      throw err;
+    });
+  });
+}
+
+function Checkpointer(src, target, id, returnValue, opts) {
+  this.src = src;
+  this.target = target;
+  this.id = id;
+  this.returnValue = returnValue;
+  this.opts = opts || {};
+}
+
+Checkpointer.prototype.writeCheckpoint = function (checkpoint, session) {
+  var self = this;
+  return this.updateTarget(checkpoint, session).then(function () {
+    return self.updateSource(checkpoint, session);
+  });
+};
+
+Checkpointer.prototype.updateTarget = function (checkpoint, session) {
+  if (this.opts.writeTargetCheckpoint) {
+    return updateCheckpoint(this.target, this.id, checkpoint,
+      session, this.returnValue);
+  } else {
+    return Promise.resolve(true);
+  }
+};
+
+Checkpointer.prototype.updateSource = function (checkpoint, session) {
+  if (this.opts.writeSourceCheckpoint) {
+    var self = this;
+    return updateCheckpoint(this.src, this.id, checkpoint,
+      session, this.returnValue)[
+      "catch"](function (err) {
+        if (isForbiddenError(err)) {
+          self.opts.writeSourceCheckpoint = false;
+          return true;
+        }
+        throw err;
+      });
+  } else {
+    return Promise.resolve(true);
+  }
+};
+
+var comparisons = {
+  "undefined": function (targetDoc, sourceDoc) {
+    // This is the previous comparison function
+    if (collate(targetDoc.last_seq, sourceDoc.last_seq) === 0) {
+      return sourceDoc.last_seq;
+    }
+    /* istanbul ignore next */
+    return 0;
+  },
+  "1": function (targetDoc, sourceDoc) {
+    // This is the comparison function ported from CouchDB
+    return compareReplicationLogs(sourceDoc, targetDoc).last_seq;
+  }
+};
+
+Checkpointer.prototype.getCheckpoint = function () {
+  var self = this;
+
+  if (self.opts && self.opts.writeSourceCheckpoint && !self.opts.writeTargetCheckpoint) {
+    return self.src.get(self.id).then(function (sourceDoc) {
+      return sourceDoc.last_seq || LOWEST_SEQ;
+    })["catch"](function (err) {
+      /* istanbul ignore if */
+      if (err.status !== 404) {
+        throw err;
+      }
+      return LOWEST_SEQ;
+    });
+  }
+
+  return self.target.get(self.id).then(function (targetDoc) {
+    if (self.opts && self.opts.writeTargetCheckpoint && !self.opts.writeSourceCheckpoint) {
+      return targetDoc.last_seq || LOWEST_SEQ;
+    }
+
+    return self.src.get(self.id).then(function (sourceDoc) {
+      // Since we can't migrate an old version doc to a new one
+      // (no session id), we just go with the lowest seq in this case
+      /* istanbul ignore if */
+      if (targetDoc.version !== sourceDoc.version) {
+        return LOWEST_SEQ;
+      }
+
+      var version;
+      if (targetDoc.version) {
+        version = targetDoc.version.toString();
+      } else {
+        version = "undefined";
+      }
+
+      if (version in comparisons) {
+        return comparisons[version](targetDoc, sourceDoc);
+      }
+      /* istanbul ignore next */
+      return LOWEST_SEQ;
+    }, function (err) {
+      if (err.status === 404 && targetDoc.last_seq) {
+        return self.src.put({
+          _id: self.id,
+          last_seq: LOWEST_SEQ
+        }).then(function () {
+          return LOWEST_SEQ;
+        }, function (err) {
+          if (isForbiddenError(err)) {
+            self.opts.writeSourceCheckpoint = false;
+            return targetDoc.last_seq;
+          }
+          /* istanbul ignore next */
+          return LOWEST_SEQ;
+        });
+      }
+      throw err;
+    });
+  })["catch"](function (err) {
+    if (err.status !== 404) {
+      throw err;
+    }
+    return LOWEST_SEQ;
+  });
+};
+// This checkpoint comparison is ported from CouchDBs source
+// they come from here:
+// https://github.com/apache/couchdb-couch-replicator/blob/master/src/couch_replicator.erl#L863-L906
+
+function compareReplicationLogs(srcDoc, tgtDoc) {
+  if (srcDoc.session_id === tgtDoc.session_id) {
+    return {
+      last_seq: srcDoc.last_seq,
+      history: srcDoc.history
+    };
+  }
+
+  return compareReplicationHistory(srcDoc.history, tgtDoc.history);
+}
+
+function compareReplicationHistory(sourceHistory, targetHistory) {
+  // the erlang loop via function arguments is not so easy to repeat in JS
+  // therefore, doing this as recursion
+  var S = sourceHistory[0];
+  var sourceRest = sourceHistory.slice(1);
+  var T = targetHistory[0];
+  var targetRest = targetHistory.slice(1);
+
+  if (!S || targetHistory.length === 0) {
+    return {
+      last_seq: LOWEST_SEQ,
+      history: []
+    };
+  }
+
+  var sourceId = S.session_id;
+  /* istanbul ignore if */
+  if (hasSessionId(sourceId, targetHistory)) {
+    return {
+      last_seq: S.last_seq,
+      history: sourceHistory
+    };
+  }
+
+  var targetId = T.session_id;
+  if (hasSessionId(targetId, sourceRest)) {
+    return {
+      last_seq: T.last_seq,
+      history: targetRest
+    };
+  }
+
+  return compareReplicationHistory(sourceRest, targetRest);
+}
+
+function hasSessionId(sessionId, history) {
+  var props = history[0];
+  var rest = history.slice(1);
+
+  if (!sessionId || history.length === 0) {
+    return false;
+  }
+
+  if (sessionId === props.session_id) {
+    return true;
+  }
+
+  return hasSessionId(sessionId, rest);
+}
+
+function isForbiddenError(err) {
+  return typeof err.status === 'number' && Math.floor(err.status / 100) === 4;
+}
+
+var STARTING_BACK_OFF = 0;
+
+function backOff(opts, returnValue, error, callback) {
+  if (opts.retry === false) {
+    returnValue.emit('error', error);
+    returnValue.removeAllListeners();
+    return;
+  }
+  /* istanbul ignore if */
+  if (typeof opts.back_off_function !== 'function') {
+    opts.back_off_function = defaultBackOff;
+  }
+  returnValue.emit('requestError', error);
+  if (returnValue.state === 'active' || returnValue.state === 'pending') {
+    returnValue.emit('paused', error);
+    returnValue.state = 'stopped';
+    var backOffSet = function backoffTimeSet() {
+      opts.current_back_off = STARTING_BACK_OFF;
+    };
+    var removeBackOffSetter = function removeBackOffTimeSet() {
+      returnValue.removeListener('active', backOffSet);
+    };
+    returnValue.once('paused', removeBackOffSetter);
+    returnValue.once('active', backOffSet);
+  }
+
+  opts.current_back_off = opts.current_back_off || STARTING_BACK_OFF;
+  opts.current_back_off = opts.back_off_function(opts.current_back_off);
+  setTimeout(callback, opts.current_back_off);
+}
+
+function sortObjectPropertiesByKey(queryParams) {
+  return Object.keys(queryParams).sort(collate).reduce(function (result, key) {
+    result[key] = queryParams[key];
+    return result;
+  }, {});
+}
+
+// Generate a unique id particular to this replication.
+// Not guaranteed to align perfectly with CouchDB's rep ids.
+function generateReplicationId(src, target, opts) {
+  var docIds = opts.doc_ids ? opts.doc_ids.sort(collate) : '';
+  var filterFun = opts.filter ? opts.filter.toString() : '';
+  var queryParams = '';
+  var filterViewName =  '';
+  var selector = '';
+
+  // possibility for checkpoints to be lost here as behaviour of
+  // JSON.stringify is not stable (see #6226)
+  /* istanbul ignore if */
+  if (opts.selector) {
+    selector = JSON.stringify(opts.selector);
+  }
+
+  if (opts.filter && opts.query_params) {
+    queryParams = JSON.stringify(sortObjectPropertiesByKey(opts.query_params));
+  }
+
+  if (opts.filter && opts.filter === '_view') {
+    filterViewName = opts.view.toString();
+  }
+
+  return Promise.all([src.id(), target.id()]).then(function (res) {
+    var queryData = res[0] + res[1] + filterFun + filterViewName +
+      queryParams + docIds + selector;
+    return new Promise(function (resolve) {
+      binaryMd5(queryData, resolve);
+    });
+  }).then(function (md5sum) {
+    // can't use straight-up md5 alphabet, because
+    // the char '/' is interpreted as being for attachments,
+    // and + is also not url-safe
+    md5sum = md5sum.replace(/\//g, '.').replace(/\+/g, '_');
+    return '_local/' + md5sum;
+  });
+}
+
+function replicate(src, target, opts, returnValue, result) {
+  var batches = [];               // list of batches to be processed
+  var currentBatch;               // the batch currently being processed
+  var pendingBatch = {
+    seq: 0,
+    changes: [],
+    docs: []
+  }; // next batch, not yet ready to be processed
+  var writingCheckpoint = false;  // true while checkpoint is being written
+  var changesCompleted = false;   // true when all changes received
+  var replicationCompleted = false; // true when replication has completed
+  var last_seq = 0;
+  var continuous = opts.continuous || opts.live || false;
+  var batch_size = opts.batch_size || 100;
+  var batches_limit = opts.batches_limit || 10;
+  var changesPending = false;     // true while src.changes is running
+  var doc_ids = opts.doc_ids;
+  var selector = opts.selector;
+  var repId;
+  var checkpointer;
+  var changedDocs = [];
+  // Like couchdb, every replication gets a unique session id
+  var session = uuid();
+
+  result = result || {
+    ok: true,
+    start_time: new Date().toISOString(),
+    docs_read: 0,
+    docs_written: 0,
+    doc_write_failures: 0,
+    errors: []
+  };
+
+  var changesOpts = {};
+  returnValue.ready(src, target);
+
+  function initCheckpointer() {
+    if (checkpointer) {
+      return Promise.resolve();
+    }
+    return generateReplicationId(src, target, opts).then(function (res) {
+      repId = res;
+
+      var checkpointOpts = {};
+      if (opts.checkpoint === false) {
+        checkpointOpts = { writeSourceCheckpoint: false, writeTargetCheckpoint: false };
+      } else if (opts.checkpoint === 'source') {
+        checkpointOpts = { writeSourceCheckpoint: true, writeTargetCheckpoint: false };
+      } else if (opts.checkpoint === 'target') {
+        checkpointOpts = { writeSourceCheckpoint: false, writeTargetCheckpoint: true };
+      } else {
+        checkpointOpts = { writeSourceCheckpoint: true, writeTargetCheckpoint: true };
+      }
+
+      checkpointer = new Checkpointer(src, target, repId, returnValue, checkpointOpts);
+    });
+  }
+
+  function writeDocs() {
+    changedDocs = [];
+
+    if (currentBatch.docs.length === 0) {
+      return;
+    }
+    var docs = currentBatch.docs;
+    var bulkOpts = {timeout: opts.timeout};
+    return target.bulkDocs({docs: docs, new_edits: false}, bulkOpts).then(function (res) {
+      /* istanbul ignore if */
+      if (returnValue.cancelled) {
+        completeReplication();
+        throw new Error('cancelled');
+      }
+
+      // `res` doesn't include full documents (which live in `docs`), so we create a map of 
+      // (id -> error), and check for errors while iterating over `docs`
+      var errorsById = Object.create(null);
+      res.forEach(function (res) {
+        if (res.error) {
+          errorsById[res.id] = res;
+        }
+      });
+
+      var errorsNo = Object.keys(errorsById).length;
+      result.doc_write_failures += errorsNo;
+      result.docs_written += docs.length - errorsNo;
+
+      docs.forEach(function (doc) {
+        var error = errorsById[doc._id];
+        if (error) {
+          result.errors.push(error);
+          // Normalize error name. i.e. 'Unauthorized' -> 'unauthorized' (eg Sync Gateway)
+          var errorName = (error.name || '').toLowerCase();
+          if (errorName === 'unauthorized' || errorName === 'forbidden') {
+            returnValue.emit('denied', clone(error));
+          } else {
+            throw error;
+          }
+        } else {
+          changedDocs.push(doc);
+        }
+      });
+
+    }, function (err) {
+      result.doc_write_failures += docs.length;
+      throw err;
+    });
+  }
+
+  function finishBatch() {
+    if (currentBatch.error) {
+      throw new Error('There was a problem getting docs.');
+    }
+    result.last_seq = last_seq = currentBatch.seq;
+    var outResult = clone(result);
+    if (changedDocs.length) {
+      outResult.docs = changedDocs;
+      // Attach 'pending' property if server supports it (CouchDB 2.0+)
+      /* istanbul ignore if */
+      if (typeof currentBatch.pending === 'number') {
+        outResult.pending = currentBatch.pending;
+        delete currentBatch.pending;
+      }
+      returnValue.emit('change', outResult);
+    }
+    writingCheckpoint = true;
+    return checkpointer.writeCheckpoint(currentBatch.seq,
+        session).then(function () {
+      writingCheckpoint = false;
+      /* istanbul ignore if */
+      if (returnValue.cancelled) {
+        completeReplication();
+        throw new Error('cancelled');
+      }
+      currentBatch = undefined;
+      getChanges();
+    })["catch"](function (err) {
+      onCheckpointError(err);
+      throw err;
+    });
+  }
+
+  function getDiffs() {
+    var diff = {};
+    currentBatch.changes.forEach(function (change) {
+      // Couchbase Sync Gateway emits these, but we can ignore them
+      /* istanbul ignore if */
+      if (change.id === "_user/") {
+        return;
+      }
+      diff[change.id] = change.changes.map(function (x) {
+        return x.rev;
+      });
+    });
+    return target.revsDiff(diff).then(function (diffs) {
+      /* istanbul ignore if */
+      if (returnValue.cancelled) {
+        completeReplication();
+        throw new Error('cancelled');
+      }
+      // currentBatch.diffs elements are deleted as the documents are written
+      currentBatch.diffs = diffs;
+    });
+  }
+
+  function getBatchDocs() {
+    return getDocs(src, target, currentBatch.diffs, returnValue).then(function (got) {
+      currentBatch.error = !got.ok;
+      got.docs.forEach(function (doc) {
+        delete currentBatch.diffs[doc._id];
+        result.docs_read++;
+        currentBatch.docs.push(doc);
+      });
+    });
+  }
+
+  function startNextBatch() {
+    if (returnValue.cancelled || currentBatch) {
+      return;
+    }
+    if (batches.length === 0) {
+      processPendingBatch(true);
+      return;
+    }
+    currentBatch = batches.shift();
+    getDiffs()
+      .then(getBatchDocs)
+      .then(writeDocs)
+      .then(finishBatch)
+      .then(startNextBatch)[
+      "catch"](function (err) {
+        abortReplication('batch processing terminated with error', err);
+      });
+  }
+
+
+  function processPendingBatch(immediate$$1) {
+    if (pendingBatch.changes.length === 0) {
+      if (batches.length === 0 && !currentBatch) {
+        if ((continuous && changesOpts.live) || changesCompleted) {
+          returnValue.state = 'pending';
+          returnValue.emit('paused');
+        }
+        if (changesCompleted) {
+          completeReplication();
+        }
+      }
+      return;
+    }
+    if (
+      immediate$$1 ||
+      changesCompleted ||
+      pendingBatch.changes.length >= batch_size
+    ) {
+      batches.push(pendingBatch);
+      pendingBatch = {
+        seq: 0,
+        changes: [],
+        docs: []
+      };
+      if (returnValue.state === 'pending' || returnValue.state === 'stopped') {
+        returnValue.state = 'active';
+        returnValue.emit('active');
+      }
+      startNextBatch();
+    }
+  }
+
+
+  function abortReplication(reason, err) {
+    if (replicationCompleted) {
+      return;
+    }
+    if (!err.message) {
+      err.message = reason;
+    }
+    result.ok = false;
+    result.status = 'aborting';
+    batches = [];
+    pendingBatch = {
+      seq: 0,
+      changes: [],
+      docs: []
+    };
+    completeReplication(err);
+  }
+
+
+  function completeReplication(fatalError) {
+    if (replicationCompleted) {
+      return;
+    }
+    /* istanbul ignore if */
+    if (returnValue.cancelled) {
+      result.status = 'cancelled';
+      if (writingCheckpoint) {
+        return;
+      }
+    }
+    result.status = result.status || 'complete';
+    result.end_time = new Date().toISOString();
+    result.last_seq = last_seq;
+    replicationCompleted = true;
+
+    if (fatalError) {
+      // need to extend the error because Firefox considers ".result" read-only
+      fatalError = createError(fatalError);
+      fatalError.result = result;
+
+      // Normalize error name. i.e. 'Unauthorized' -> 'unauthorized' (eg Sync Gateway)
+      var errorName = (fatalError.name || '').toLowerCase();
+      if (errorName === 'unauthorized' || errorName === 'forbidden') {
+        returnValue.emit('error', fatalError);
+        returnValue.removeAllListeners();
+      } else {
+        backOff(opts, returnValue, fatalError, function () {
+          replicate(src, target, opts, returnValue);
+        });
+      }
+    } else {
+      returnValue.emit('complete', result);
+      returnValue.removeAllListeners();
+    }
+  }
+
+
+  function onChange(change, pending, lastSeq) {
+    /* istanbul ignore if */
+    if (returnValue.cancelled) {
+      return completeReplication();
+    }
+    // Attach 'pending' property if server supports it (CouchDB 2.0+)
+    /* istanbul ignore if */
+    if (typeof pending === 'number') {
+      pendingBatch.pending = pending;
+    }
+
+    var filter = filterChange(opts)(change);
+    if (!filter) {
+      return;
+    }
+    pendingBatch.seq = change.seq || lastSeq;
+    pendingBatch.changes.push(change);
+    immediate(function () {
+      processPendingBatch(batches.length === 0 && changesOpts.live);
+    });
+  }
+
+
+  function onChangesComplete(changes) {
+    changesPending = false;
+    /* istanbul ignore if */
+    if (returnValue.cancelled) {
+      return completeReplication();
+    }
+
+    // if no results were returned then we're done,
+    // else fetch more
+    if (changes.results.length > 0) {
+      changesOpts.since = changes.results[changes.results.length - 1].seq;
+      getChanges();
+      processPendingBatch(true);
+    } else {
+
+      var complete = function () {
+        if (continuous) {
+          changesOpts.live = true;
+          getChanges();
+        } else {
+          changesCompleted = true;
+        }
+        processPendingBatch(true);
+      };
+
+      // update the checkpoint so we start from the right seq next time
+      if (!currentBatch && changes.results.length === 0) {
+        writingCheckpoint = true;
+        checkpointer.writeCheckpoint(changes.last_seq,
+            session).then(function () {
+          writingCheckpoint = false;
+          result.last_seq = last_seq = changes.last_seq;
+          complete();
+        })[
+        "catch"](onCheckpointError);
+      } else {
+        complete();
+      }
+    }
+  }
+
+
+  function onChangesError(err) {
+    changesPending = false;
+    /* istanbul ignore if */
+    if (returnValue.cancelled) {
+      return completeReplication();
+    }
+    abortReplication('changes rejected', err);
+  }
+
+
+  function getChanges() {
+    if (!(
+      !changesPending &&
+      !changesCompleted &&
+      batches.length < batches_limit
+      )) {
+      return;
+    }
+    changesPending = true;
+    function abortChanges() {
+      changes.cancel();
+    }
+    function removeListener() {
+      returnValue.removeListener('cancel', abortChanges);
+    }
+
+    if (returnValue._changes) { // remove old changes() and listeners
+      returnValue.removeListener('cancel', returnValue._abortChanges);
+      returnValue._changes.cancel();
+    }
+    returnValue.once('cancel', abortChanges);
+
+    var changes = src.changes(changesOpts)
+      .on('change', onChange);
+    changes.then(removeListener, removeListener);
+    changes.then(onChangesComplete)[
+      "catch"](onChangesError);
+
+    if (opts.retry) {
+      // save for later so we can cancel if necessary
+      returnValue._changes = changes;
+      returnValue._abortChanges = abortChanges;
+    }
+  }
+
+
+  function startChanges() {
+    initCheckpointer().then(function () {
+      /* istanbul ignore if */
+      if (returnValue.cancelled) {
+        completeReplication();
+        return;
+      }
+      return checkpointer.getCheckpoint().then(function (checkpoint) {
+        last_seq = checkpoint;
+        changesOpts = {
+          since: last_seq,
+          limit: batch_size,
+          batch_size: batch_size,
+          style: 'all_docs',
+          doc_ids: doc_ids,
+          selector: selector,
+          return_docs: true // required so we know when we're done
+        };
+        if (opts.filter) {
+          if (typeof opts.filter !== 'string') {
+            // required for the client-side filter in onChange
+            changesOpts.include_docs = true;
+          } else { // ddoc filter
+            changesOpts.filter = opts.filter;
+          }
+        }
+        if ('heartbeat' in opts) {
+          changesOpts.heartbeat = opts.heartbeat;
+        }
+        if ('timeout' in opts) {
+          changesOpts.timeout = opts.timeout;
+        }
+        if (opts.query_params) {
+          changesOpts.query_params = opts.query_params;
+        }
+        if (opts.view) {
+          changesOpts.view = opts.view;
+        }
+        getChanges();
+      });
+    })["catch"](function (err) {
+      abortReplication('getCheckpoint rejected with ', err);
+    });
+  }
+
+  /* istanbul ignore next */
+  function onCheckpointError(err) {
+    writingCheckpoint = false;
+    abortReplication('writeCheckpoint completed with error', err);
+  }
+
+  /* istanbul ignore if */
+  if (returnValue.cancelled) { // cancelled immediately
+    completeReplication();
+    return;
+  }
+
+  if (!returnValue._addedListeners) {
+    returnValue.once('cancel', completeReplication);
+
+    if (typeof opts.complete === 'function') {
+      returnValue.once('error', opts.complete);
+      returnValue.once('complete', function (result) {
+        opts.complete(null, result);
+      });
+    }
+    returnValue._addedListeners = true;
+  }
+
+  if (typeof opts.since === 'undefined') {
+    startChanges();
+  } else {
+    initCheckpointer().then(function () {
+      writingCheckpoint = true;
+      return checkpointer.writeCheckpoint(opts.since, session);
+    }).then(function () {
+      writingCheckpoint = false;
+      /* istanbul ignore if */
+      if (returnValue.cancelled) {
+        completeReplication();
+        return;
+      }
+      last_seq = opts.since;
+      startChanges();
+    })["catch"](onCheckpointError);
+  }
+}
+
+// We create a basic promise so the caller can cancel the replication possibly
+// before we have actually started listening to changes etc
+inherits(Replication, events.EventEmitter);
+function Replication() {
+  events.EventEmitter.call(this);
+  this.cancelled = false;
+  this.state = 'pending';
+  var self = this;
+  var promise = new Promise(function (fulfill, reject) {
+    self.once('complete', fulfill);
+    self.once('error', reject);
+  });
+  self.then = function (resolve, reject) {
+    return promise.then(resolve, reject);
+  };
+  self["catch"] = function (reject) {
+    return promise["catch"](reject);
+  };
+  // As we allow error handling via "error" event as well,
+  // put a stub in here so that rejecting never throws UnhandledError.
+  self["catch"](function () {});
+}
+
+Replication.prototype.cancel = function () {
+  this.cancelled = true;
+  this.state = 'cancelled';
+  this.emit('cancel');
+};
+
+Replication.prototype.ready = function (src, target) {
+  var self = this;
+  if (self._readyCalled) {
+    return;
+  }
+  self._readyCalled = true;
+
+  function onDestroy() {
+    self.cancel();
+  }
+  src.once('destroyed', onDestroy);
+  target.once('destroyed', onDestroy);
+  function cleanup() {
+    src.removeListener('destroyed', onDestroy);
+    target.removeListener('destroyed', onDestroy);
+  }
+  self.once('complete', cleanup);
+};
+
+function toPouch(db, opts) {
+  var PouchConstructor = opts.PouchConstructor;
+  if (typeof db === 'string') {
+    return new PouchConstructor(db, opts);
+  } else {
+    return db;
+  }
+}
+
+function replicateWrapper(src, target, opts, callback) {
+
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+  if (typeof opts === 'undefined') {
+    opts = {};
+  }
+
+  if (opts.doc_ids && !Array.isArray(opts.doc_ids)) {
+    throw createError(BAD_REQUEST,
+                       "`doc_ids` filter parameter is not a list.");
+  }
+
+  opts.complete = callback;
+  opts = clone(opts);
+  opts.continuous = opts.continuous || opts.live;
+  opts.retry = ('retry' in opts) ? opts.retry : false;
+  /*jshint validthis:true */
+  opts.PouchConstructor = opts.PouchConstructor || this;
+  var replicateRet = new Replication(opts);
+  var srcPouch = toPouch(src, opts);
+  var targetPouch = toPouch(target, opts);
+  replicate(srcPouch, targetPouch, opts, replicateRet);
+  return replicateRet;
+}
+
+inherits(Sync, events.EventEmitter);
+function sync(src, target, opts, callback) {
+  if (typeof opts === 'function') {
+    callback = opts;
+    opts = {};
+  }
+  if (typeof opts === 'undefined') {
+    opts = {};
+  }
+  opts = clone(opts);
+  /*jshint validthis:true */
+  opts.PouchConstructor = opts.PouchConstructor || this;
+  src = toPouch(src, opts);
+  target = toPouch(target, opts);
+  return new Sync(src, target, opts, callback);
+}
+
+function Sync(src, target, opts, callback) {
+  var self = this;
+  this.canceled = false;
+
+  var optsPush = opts.push ? $inject_Object_assign({}, opts, opts.push) : opts;
+  var optsPull = opts.pull ? $inject_Object_assign({}, opts, opts.pull) : opts;
+
+  this.push = replicateWrapper(src, target, optsPush);
+  this.pull = replicateWrapper(target, src, optsPull);
+
+  this.pushPaused = true;
+  this.pullPaused = true;
+
+  function pullChange(change) {
+    self.emit('change', {
+      direction: 'pull',
+      change: change
+    });
+  }
+  function pushChange(change) {
+    self.emit('change', {
+      direction: 'push',
+      change: change
+    });
+  }
+  function pushDenied(doc) {
+    self.emit('denied', {
+      direction: 'push',
+      doc: doc
+    });
+  }
+  function pullDenied(doc) {
+    self.emit('denied', {
+      direction: 'pull',
+      doc: doc
+    });
+  }
+  function pushPaused() {
+    self.pushPaused = true;
+    /* istanbul ignore if */
+    if (self.pullPaused) {
+      self.emit('paused');
+    }
+  }
+  function pullPaused() {
+    self.pullPaused = true;
+    /* istanbul ignore if */
+    if (self.pushPaused) {
+      self.emit('paused');
+    }
+  }
+  function pushActive() {
+    self.pushPaused = false;
+    /* istanbul ignore if */
+    if (self.pullPaused) {
+      self.emit('active', {
+        direction: 'push'
+      });
+    }
+  }
+  function pullActive() {
+    self.pullPaused = false;
+    /* istanbul ignore if */
+    if (self.pushPaused) {
+      self.emit('active', {
+        direction: 'pull'
+      });
+    }
+  }
+
+  var removed = {};
+
+  function removeAll(type) { // type is 'push' or 'pull'
+    return function (event, func) {
+      var isChange = event === 'change' &&
+        (func === pullChange || func === pushChange);
+      var isDenied = event === 'denied' &&
+        (func === pullDenied || func === pushDenied);
+      var isPaused = event === 'paused' &&
+        (func === pullPaused || func === pushPaused);
+      var isActive = event === 'active' &&
+        (func === pullActive || func === pushActive);
+
+      if (isChange || isDenied || isPaused || isActive) {
+        if (!(event in removed)) {
+          removed[event] = {};
+        }
+        removed[event][type] = true;
+        if (Object.keys(removed[event]).length === 2) {
+          // both push and pull have asked to be removed
+          self.removeAllListeners(event);
+        }
+      }
+    };
+  }
+
+  if (opts.live) {
+    this.push.on('complete', self.pull.cancel.bind(self.pull));
+    this.pull.on('complete', self.push.cancel.bind(self.push));
+  }
+
+  function addOneListener(ee, event, listener) {
+    if (ee.listeners(event).indexOf(listener) == -1) {
+      ee.on(event, listener);
+    }
+  }
+
+  this.on('newListener', function (event) {
+    if (event === 'change') {
+      addOneListener(self.pull, 'change', pullChange);
+      addOneListener(self.push, 'change', pushChange);
+    } else if (event === 'denied') {
+      addOneListener(self.pull, 'denied', pullDenied);
+      addOneListener(self.push, 'denied', pushDenied);
+    } else if (event === 'active') {
+      addOneListener(self.pull, 'active', pullActive);
+      addOneListener(self.push, 'active', pushActive);
+    } else if (event === 'paused') {
+      addOneListener(self.pull, 'paused', pullPaused);
+      addOneListener(self.push, 'paused', pushPaused);
+    }
+  });
+
+  this.on('removeListener', function (event) {
+    if (event === 'change') {
+      self.pull.removeListener('change', pullChange);
+      self.push.removeListener('change', pushChange);
+    } else if (event === 'denied') {
+      self.pull.removeListener('denied', pullDenied);
+      self.push.removeListener('denied', pushDenied);
+    } else if (event === 'active') {
+      self.pull.removeListener('active', pullActive);
+      self.push.removeListener('active', pushActive);
+    } else if (event === 'paused') {
+      self.pull.removeListener('paused', pullPaused);
+      self.push.removeListener('paused', pushPaused);
+    }
+  });
+
+  this.pull.on('removeListener', removeAll('pull'));
+  this.push.on('removeListener', removeAll('push'));
+
+  var promise = Promise.all([
+    this.push,
+    this.pull
+  ]).then(function (resp) {
+    var out = {
+      push: resp[0],
+      pull: resp[1]
+    };
+    self.emit('complete', out);
+    if (callback) {
+      callback(null, out);
+    }
+    self.removeAllListeners();
+    return out;
+  }, function (err) {
+    self.cancel();
+    if (callback) {
+      // if there's a callback, then the callback can receive
+      // the error event
+      callback(err);
+    } else {
+      // if there's no callback, then we're safe to emit an error
+      // event, which would otherwise throw an unhandled error
+      // due to 'error' being a special event in EventEmitters
+      self.emit('error', err);
+    }
+    self.removeAllListeners();
+    if (callback) {
+      // no sense throwing if we're already emitting an 'error' event
+      throw err;
+    }
+  });
+
+  this.then = function (success, err) {
+    return promise.then(success, err);
+  };
+
+  this["catch"] = function (err) {
+    return promise["catch"](err);
+  };
+}
+
+Sync.prototype.cancel = function () {
+  if (!this.canceled) {
+    this.canceled = true;
+    this.push.cancel();
+    this.pull.cancel();
+  }
+};
+
+function replication(PouchDB) {
+  PouchDB.replicate = replicateWrapper;
+  PouchDB.sync = sync;
+
+  Object.defineProperty(PouchDB.prototype, 'replicate', {
+    get: function () {
+      var self = this;
+      if (typeof this.replicateMethods === 'undefined') {
+        this.replicateMethods = {
+          from: function (other, opts, callback) {
+            return self.constructor.replicate(other, self, opts, callback);
+          },
+          to: function (other, opts, callback) {
+            return self.constructor.replicate(self, other, opts, callback);
+          }
+        };
+      }
+      return this.replicateMethods;
+    }
+  });
+
+  PouchDB.prototype.sync = function (dbName, opts, callback) {
+    return this.constructor.sync(this, dbName, opts, callback);
+  };
+}
+
+PouchDB.plugin(IDBPouch)
+  .plugin(HttpPouch$1)
+  .plugin(mapreduce)
+  .plugin(replication);
+
+// Pull from src because pouchdb-node/pouchdb-browser themselves
+
+module.exports = PouchDB;
+
+}).call(this,_dereq_(5),typeof global !== "undefined" ? global : typeof self !== "undefined" ? self : typeof window !== "undefined" ? window : {})
+},{"1":1,"12":12,"2":2,"3":3,"4":4,"5":5,"6":6,"7":7}]},{},[13])(13)
+});