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backbone.js (77794B)

---

 //     Backbone.js 1.4.0
 
 //     (c) 2010-2019 Jeremy Ashkenas and DocumentCloud
 //     Backbone may be freely distributed under the MIT license.
 //     For all details and documentation:
 //     http://backbonejs.org
 
 (function(factory) {
 
   // Establish the root object, `window` (`self`) in the browser, or `global` on the server.
   // We use `self` instead of `window` for `WebWorker` support.
   var root = typeof self == 'object' && self.self === self && self ||
             typeof global == 'object' && global.global === global && global;
 
   // Set up Backbone appropriately for the environment. Start with AMD.
   if (typeof define === 'function' && define.amd) {
     define(['underscore', 'jquery', 'exports'], function(_, $, exports) {
       // Export global even in AMD case in case this script is loaded with
       // others that may still expect a global Backbone.
       root.Backbone = factory(root, exports, _, $);
     });
 
   // Next for Node.js or CommonJS. jQuery may not be needed as a module.
   } else if (typeof exports !== 'undefined') {
     var _ = require('underscore'), $;
     try { $ = require('jquery'); } catch (e) {}
     factory(root, exports, _, $);
 
   // Finally, as a browser global.
   } else {
     root.Backbone = factory(root, {}, root._, root.jQuery || root.Zepto || root.ender || root.$);
   }
 
 })(function(root, Backbone, _, $) {
 
   // Initial Setup
   // -------------
 
   // Save the previous value of the `Backbone` variable, so that it can be
   // restored later on, if `noConflict` is used.
   var previousBackbone = root.Backbone;
 
   // Create a local reference to a common array method we'll want to use later.
   var slice = Array.prototype.slice;
 
   // Current version of the library. Keep in sync with `package.json`.
   Backbone.VERSION = '1.4.0';
 
   // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns
   // the `$` variable.
   Backbone.$ = $;
 
   // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
   // to its previous owner. Returns a reference to this Backbone object.
   Backbone.noConflict = function() {
     root.Backbone = previousBackbone;
     return this;
   };
 
   // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option
   // will fake `"PATCH"`, `"PUT"` and `"DELETE"` requests via the `_method` parameter and
   // set a `X-Http-Method-Override` header.
   Backbone.emulateHTTP = false;
 
   // Turn on `emulateJSON` to support legacy servers that can't deal with direct
   // `application/json` requests ... this will encode the body as
   // `application/x-www-form-urlencoded` instead and will send the model in a
   // form param named `model`.
   Backbone.emulateJSON = false;
 
   // Backbone.Events
   // ---------------
 
   // A module that can be mixed in to *any object* in order to provide it with
   // a custom event channel. You may bind a callback to an event with `on` or
   // remove with `off`; `trigger`-ing an event fires all callbacks in
   // succession.
   //
   //     var object = {};
   //     _.extend(object, Backbone.Events);
   //     object.on('expand', function(){ alert('expanded'); });
   //     object.trigger('expand');
   //
   var Events = Backbone.Events = {};
 
   // Regular expression used to split event strings.
   var eventSplitter = /\s+/;
 
   // A private global variable to share between listeners and listenees.
   var _listening;
 
   // Iterates over the standard `event, callback` (as well as the fancy multiple
   // space-separated events `"change blur", callback` and jQuery-style event
   // maps `{event: callback}`).
   var eventsApi = function(iteratee, events, name, callback, opts) {
     var i = 0, names;
     if (name && typeof name === 'object') {
       // Handle event maps.
       if (callback !== void 0 && 'context' in opts && opts.context === void 0) opts.context = callback;
       for (names = _.keys(name); i < names.length ; i++) {
         events = eventsApi(iteratee, events, names[i], name[names[i]], opts);
       }
     } else if (name && eventSplitter.test(name)) {
       // Handle space-separated event names by delegating them individually.
       for (names = name.split(eventSplitter); i < names.length; i++) {
         events = iteratee(events, names[i], callback, opts);
       }
     } else {
       // Finally, standard events.
       events = iteratee(events, name, callback, opts);
     }
     return events;
   };
 
   // Bind an event to a `callback` function. Passing `"all"` will bind
   // the callback to all events fired.
   Events.on = function(name, callback, context) {
     this._events = eventsApi(onApi, this._events || {}, name, callback, {
       context: context,
       ctx: this,
       listening: _listening
     });
 
     if (_listening) {
       var listeners = this._listeners || (this._listeners = {});
       listeners[_listening.id] = _listening;
       // Allow the listening to use a counter, instead of tracking
       // callbacks for library interop
       _listening.interop = false;
     }
 
     return this;
   };
 
   // Inversion-of-control versions of `on`. Tell *this* object to listen to
   // an event in another object... keeping track of what it's listening to
   // for easier unbinding later.
   Events.listenTo = function(obj, name, callback) {
     if (!obj) return this;
     var id = obj._listenId || (obj._listenId = _.uniqueId('l'));
     var listeningTo = this._listeningTo || (this._listeningTo = {});
     var listening = _listening = listeningTo[id];
 
     // This object is not listening to any other events on `obj` yet.
     // Setup the necessary references to track the listening callbacks.
     if (!listening) {
       this._listenId || (this._listenId = _.uniqueId('l'));
       listening = _listening = listeningTo[id] = new Listening(this, obj);
     }
 
     // Bind callbacks on obj.
     var error = tryCatchOn(obj, name, callback, this);
     _listening = void 0;
 
     if (error) throw error;
     // If the target obj is not Backbone.Events, track events manually.
     if (listening.interop) listening.on(name, callback);
 
     return this;
   };
 
   // The reducing API that adds a callback to the `events` object.
   var onApi = function(events, name, callback, options) {
     if (callback) {
       var handlers = events[name] || (events[name] = []);
       var context = options.context, ctx = options.ctx, listening = options.listening;
       if (listening) listening.count++;
 
       handlers.push({callback: callback, context: context, ctx: context || ctx, listening: listening});
     }
     return events;
   };
 
   // An try-catch guarded #on function, to prevent poisoning the global
   // `_listening` variable.
   var tryCatchOn = function(obj, name, callback, context) {
     try {
       obj.on(name, callback, context);
     } catch (e) {
       return e;
     }
   };
 
   // Remove one or many callbacks. If `context` is null, removes all
   // callbacks with that function. If `callback` is null, removes all
   // callbacks for the event. If `name` is null, removes all bound
   // callbacks for all events.
   Events.off = function(name, callback, context) {
     if (!this._events) return this;
     this._events = eventsApi(offApi, this._events, name, callback, {
       context: context,
       listeners: this._listeners
     });
 
     return this;
   };
 
   // Tell this object to stop listening to either specific events ... or
   // to every object it's currently listening to.
   Events.stopListening = function(obj, name, callback) {
     var listeningTo = this._listeningTo;
     if (!listeningTo) return this;
 
     var ids = obj ? [obj._listenId] : _.keys(listeningTo);
     for (var i = 0; i < ids.length; i++) {
       var listening = listeningTo[ids[i]];
 
       // If listening doesn't exist, this object is not currently
       // listening to obj. Break out early.
       if (!listening) break;
 
       listening.obj.off(name, callback, this);
       if (listening.interop) listening.off(name, callback);
     }
     if (_.isEmpty(listeningTo)) this._listeningTo = void 0;
 
     return this;
   };
 
   // The reducing API that removes a callback from the `events` object.
   var offApi = function(events, name, callback, options) {
     if (!events) return;
 
     var context = options.context, listeners = options.listeners;
     var i = 0, names;
 
     // Delete all event listeners and "drop" events.
     if (!name && !context && !callback) {
       for (names = _.keys(listeners); i < names.length; i++) {
         listeners[names[i]].cleanup();
       }
       return;
     }
 
     names = name ? [name] : _.keys(events);
     for (; i < names.length; i++) {
       name = names[i];
       var handlers = events[name];
 
       // Bail out if there are no events stored.
       if (!handlers) break;
 
       // Find any remaining events.
       var remaining = [];
       for (var j = 0; j < handlers.length; j++) {
         var handler = handlers[j];
         if (
           callback && callback !== handler.callback &&
             callback !== handler.callback._callback ||
               context && context !== handler.context
         ) {
           remaining.push(handler);
         } else {
           var listening = handler.listening;
           if (listening) listening.off(name, callback);
         }
       }
 
       // Replace events if there are any remaining.  Otherwise, clean up.
       if (remaining.length) {
         events[name] = remaining;
       } else {
         delete events[name];
       }
     }
 
     return events;
   };
 
   // Bind an event to only be triggered a single time. After the first time
   // the callback is invoked, its listener will be removed. If multiple events
   // are passed in using the space-separated syntax, the handler will fire
   // once for each event, not once for a combination of all events.
   Events.once = function(name, callback, context) {
     // Map the event into a `{event: once}` object.
     var events = eventsApi(onceMap, {}, name, callback, this.off.bind(this));
     if (typeof name === 'string' && context == null) callback = void 0;
     return this.on(events, callback, context);
   };
 
   // Inversion-of-control versions of `once`.
   Events.listenToOnce = function(obj, name, callback) {
     // Map the event into a `{event: once}` object.
     var events = eventsApi(onceMap, {}, name, callback, this.stopListening.bind(this, obj));
     return this.listenTo(obj, events);
   };
 
   // Reduces the event callbacks into a map of `{event: onceWrapper}`.
   // `offer` unbinds the `onceWrapper` after it has been called.
   var onceMap = function(map, name, callback, offer) {
     if (callback) {
       var once = map[name] = _.once(function() {
         offer(name, once);
         callback.apply(this, arguments);
       });
       once._callback = callback;
     }
     return map;
   };
 
   // Trigger one or many events, firing all bound callbacks. Callbacks are
   // passed the same arguments as `trigger` is, apart from the event name
   // (unless you're listening on `"all"`, which will cause your callback to
   // receive the true name of the event as the first argument).
   Events.trigger = function(name) {
     if (!this._events) return this;
 
     var length = Math.max(0, arguments.length - 1);
     var args = Array(length);
     for (var i = 0; i < length; i++) args[i] = arguments[i + 1];
 
     eventsApi(triggerApi, this._events, name, void 0, args);
     return this;
   };
 
   // Handles triggering the appropriate event callbacks.
   var triggerApi = function(objEvents, name, callback, args) {
     if (objEvents) {
       var events = objEvents[name];
       var allEvents = objEvents.all;
       if (events && allEvents) allEvents = allEvents.slice();
       if (events) triggerEvents(events, args);
       if (allEvents) triggerEvents(allEvents, [name].concat(args));
     }
     return objEvents;
   };
 
   // A difficult-to-believe, but optimized internal dispatch function for
   // triggering events. Tries to keep the usual cases speedy (most internal
   // Backbone events have 3 arguments).
   var triggerEvents = function(events, args) {
     var ev, i = -1, l = events.length, a1 = args[0], a2 = args[1], a3 = args[2];
     switch (args.length) {
       case 0: while (++i < l) (ev = events[i]).callback.call(ev.ctx); return;
       case 1: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1); return;
       case 2: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2); return;
       case 3: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2, a3); return;
       default: while (++i < l) (ev = events[i]).callback.apply(ev.ctx, args); return;
     }
   };
 
   // A listening class that tracks and cleans up memory bindings
   // when all callbacks have been offed.
   var Listening = function(listener, obj) {
     this.id = listener._listenId;
     this.listener = listener;
     this.obj = obj;
     this.interop = true;
     this.count = 0;
     this._events = void 0;
   };
 
   Listening.prototype.on = Events.on;
 
   // Offs a callback (or several).
   // Uses an optimized counter if the listenee uses Backbone.Events.
   // Otherwise, falls back to manual tracking to support events
   // library interop.
   Listening.prototype.off = function(name, callback) {
     var cleanup;
     if (this.interop) {
       this._events = eventsApi(offApi, this._events, name, callback, {
         context: void 0,
         listeners: void 0
       });
       cleanup = !this._events;
     } else {
       this.count--;
       cleanup = this.count === 0;
     }
     if (cleanup) this.cleanup();
   };
 
   // Cleans up memory bindings between the listener and the listenee.
   Listening.prototype.cleanup = function() {
     delete this.listener._listeningTo[this.obj._listenId];
     if (!this.interop) delete this.obj._listeners[this.id];
   };
 
   // Aliases for backwards compatibility.
   Events.bind   = Events.on;
   Events.unbind = Events.off;
 
   // Allow the `Backbone` object to serve as a global event bus, for folks who
   // want global "pubsub" in a convenient place.
   _.extend(Backbone, Events);
 
   // Backbone.Model
   // --------------
 
   // Backbone **Models** are the basic data object in the framework --
   // frequently representing a row in a table in a database on your server.
   // A discrete chunk of data and a bunch of useful, related methods for
   // performing computations and transformations on that data.
 
   // Create a new model with the specified attributes. A client id (`cid`)
   // is automatically generated and assigned for you.
   var Model = Backbone.Model = function(attributes, options) {
     var attrs = attributes || {};
     options || (options = {});
     this.preinitialize.apply(this, arguments);
     this.cid = _.uniqueId(this.cidPrefix);
     this.attributes = {};
     if (options.collection) this.collection = options.collection;
     if (options.parse) attrs = this.parse(attrs, options) || {};
     var defaults = _.result(this, 'defaults');
     attrs = _.defaults(_.extend({}, defaults, attrs), defaults);
     this.set(attrs, options);
     this.changed = {};
     this.initialize.apply(this, arguments);
   };
 
   // Attach all inheritable methods to the Model prototype.
   _.extend(Model.prototype, Events, {
 
     // A hash of attributes whose current and previous value differ.
     changed: null,
 
     // The value returned during the last failed validation.
     validationError: null,
 
     // The default name for the JSON `id` attribute is `"id"`. MongoDB and
     // CouchDB users may want to set this to `"_id"`.
     idAttribute: 'id',
 
     // The prefix is used to create the client id which is used to identify models locally.
     // You may want to override this if you're experiencing name clashes with model ids.
     cidPrefix: 'c',
 
     // preinitialize is an empty function by default. You can override it with a function
     // or object.  preinitialize will run before any instantiation logic is run in the Model.
     preinitialize: function(){},
 
     // Initialize is an empty function by default. Override it with your own
     // initialization logic.
     initialize: function(){},
 
     // Return a copy of the model's `attributes` object.
     toJSON: function(options) {
       return _.clone(this.attributes);
     },
 
     // Proxy `Backbone.sync` by default -- but override this if you need
     // custom syncing semantics for *this* particular model.
     sync: function() {
       return Backbone.sync.apply(this, arguments);
     },
 
     // Get the value of an attribute.
     get: function(attr) {
       return this.attributes[attr];
     },
 
     // Get the HTML-escaped value of an attribute.
     escape: function(attr) {
       return _.escape(this.get(attr));
     },
 
     // Returns `true` if the attribute contains a value that is not null
     // or undefined.
     has: function(attr) {
       return this.get(attr) != null;
     },
 
     // Special-cased proxy to underscore's `_.matches` method.
     matches: function(attrs) {
       return !!_.iteratee(attrs, this)(this.attributes);
     },
 
     // Set a hash of model attributes on the object, firing `"change"`. This is
     // the core primitive operation of a model, updating the data and notifying
     // anyone who needs to know about the change in state. The heart of the beast.
     set: function(key, val, options) {
       if (key == null) return this;
 
       // Handle both `"key", value` and `{key: value}` -style arguments.
       var attrs;
       if (typeof key === 'object') {
         attrs = key;
         options = val;
       } else {
         (attrs = {})[key] = val;
       }
 
       options || (options = {});
 
       // Run validation.
       if (!this._validate(attrs, options)) return false;
 
       // Extract attributes and options.
       var unset      = options.unset;
       var silent     = options.silent;
       var changes    = [];
       var changing   = this._changing;
       this._changing = true;
 
       if (!changing) {
         this._previousAttributes = _.clone(this.attributes);
         this.changed = {};
       }
 
       var current = this.attributes;
       var changed = this.changed;
       var prev    = this._previousAttributes;
 
       // For each `set` attribute, update or delete the current value.
       for (var attr in attrs) {
         val = attrs[attr];
         if (!_.isEqual(current[attr], val)) changes.push(attr);
         if (!_.isEqual(prev[attr], val)) {
           changed[attr] = val;
         } else {
           delete changed[attr];
         }
         unset ? delete current[attr] : current[attr] = val;
       }
 
       // Update the `id`.
       if (this.idAttribute in attrs) this.id = this.get(this.idAttribute);
 
       // Trigger all relevant attribute changes.
       if (!silent) {
         if (changes.length) this._pending = options;
         for (var i = 0; i < changes.length; i++) {
           this.trigger('change:' + changes[i], this, current[changes[i]], options);
         }
       }
 
       // You might be wondering why there's a `while` loop here. Changes can
       // be recursively nested within `"change"` events.
       if (changing) return this;
       if (!silent) {
         while (this._pending) {
           options = this._pending;
           this._pending = false;
           this.trigger('change', this, options);
         }
       }
       this._pending = false;
       this._changing = false;
       return this;
     },
 
     // Remove an attribute from the model, firing `"change"`. `unset` is a noop
     // if the attribute doesn't exist.
     unset: function(attr, options) {
       return this.set(attr, void 0, _.extend({}, options, {unset: true}));
     },
 
     // Clear all attributes on the model, firing `"change"`.
     clear: function(options) {
       var attrs = {};
       for (var key in this.attributes) attrs[key] = void 0;
       return this.set(attrs, _.extend({}, options, {unset: true}));
     },
 
     // Determine if the model has changed since the last `"change"` event.
     // If you specify an attribute name, determine if that attribute has changed.
     hasChanged: function(attr) {
       if (attr == null) return !_.isEmpty(this.changed);
       return _.has(this.changed, attr);
     },
 
     // Return an object containing all the attributes that have changed, or
     // false if there are no changed attributes. Useful for determining what
     // parts of a view need to be updated and/or what attributes need to be
     // persisted to the server. Unset attributes will be set to undefined.
     // You can also pass an attributes object to diff against the model,
     // determining if there *would be* a change.
     changedAttributes: function(diff) {
       if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
       var old = this._changing ? this._previousAttributes : this.attributes;
       var changed = {};
       var hasChanged;
       for (var attr in diff) {
         var val = diff[attr];
         if (_.isEqual(old[attr], val)) continue;
         changed[attr] = val;
         hasChanged = true;
       }
       return hasChanged ? changed : false;
     },
 
     // Get the previous value of an attribute, recorded at the time the last
     // `"change"` event was fired.
     previous: function(attr) {
       if (attr == null || !this._previousAttributes) return null;
       return this._previousAttributes[attr];
     },
 
     // Get all of the attributes of the model at the time of the previous
     // `"change"` event.
     previousAttributes: function() {
       return _.clone(this._previousAttributes);
     },
 
     // Fetch the model from the server, merging the response with the model's
     // local attributes. Any changed attributes will trigger a "change" event.
     fetch: function(options) {
       options = _.extend({parse: true}, options);
       var model = this;
       var success = options.success;
       options.success = function(resp) {
         var serverAttrs = options.parse ? model.parse(resp, options) : resp;
         if (!model.set(serverAttrs, options)) return false;
         if (success) success.call(options.context, model, resp, options);
         model.trigger('sync', model, resp, options);
       };
       wrapError(this, options);
       return this.sync('read', this, options);
     },
 
     // Set a hash of model attributes, and sync the model to the server.
     // If the server returns an attributes hash that differs, the model's
     // state will be `set` again.
     save: function(key, val, options) {
       // Handle both `"key", value` and `{key: value}` -style arguments.
       var attrs;
       if (key == null || typeof key === 'object') {
         attrs = key;
         options = val;
       } else {
         (attrs = {})[key] = val;
       }
 
       options = _.extend({validate: true, parse: true}, options);
       var wait = options.wait;
 
       // If we're not waiting and attributes exist, save acts as
       // `set(attr).save(null, opts)` with validation. Otherwise, check if
       // the model will be valid when the attributes, if any, are set.
       if (attrs && !wait) {
         if (!this.set(attrs, options)) return false;
       } else if (!this._validate(attrs, options)) {
         return false;
       }
 
       // After a successful server-side save, the client is (optionally)
       // updated with the server-side state.
       var model = this;
       var success = options.success;
       var attributes = this.attributes;
       options.success = function(resp) {
         // Ensure attributes are restored during synchronous saves.
         model.attributes = attributes;
         var serverAttrs = options.parse ? model.parse(resp, options) : resp;
         if (wait) serverAttrs = _.extend({}, attrs, serverAttrs);
         if (serverAttrs && !model.set(serverAttrs, options)) return false;
         if (success) success.call(options.context, model, resp, options);
         model.trigger('sync', model, resp, options);
       };
       wrapError(this, options);
 
       // Set temporary attributes if `{wait: true}` to properly find new ids.
       if (attrs && wait) this.attributes = _.extend({}, attributes, attrs);
 
       var method = this.isNew() ? 'create' : options.patch ? 'patch' : 'update';
       if (method === 'patch' && !options.attrs) options.attrs = attrs;
       var xhr = this.sync(method, this, options);
 
       // Restore attributes.
       this.attributes = attributes;
 
       return xhr;
     },
 
     // Destroy this model on the server if it was already persisted.
     // Optimistically removes the model from its collection, if it has one.
     // If `wait: true` is passed, waits for the server to respond before removal.
     destroy: function(options) {
       options = options ? _.clone(options) : {};
       var model = this;
       var success = options.success;
       var wait = options.wait;
 
       var destroy = function() {
         model.stopListening();
         model.trigger('destroy', model, model.collection, options);
       };
 
       options.success = function(resp) {
         if (wait) destroy();
         if (success) success.call(options.context, model, resp, options);
         if (!model.isNew()) model.trigger('sync', model, resp, options);
       };
 
       var xhr = false;
       if (this.isNew()) {
         _.defer(options.success);
       } else {
         wrapError(this, options);
         xhr = this.sync('delete', this, options);
       }
       if (!wait) destroy();
       return xhr;
     },
 
     // Default URL for the model's representation on the server -- if you're
     // using Backbone's restful methods, override this to change the endpoint
     // that will be called.
     url: function() {
       var base =
         _.result(this, 'urlRoot') ||
         _.result(this.collection, 'url') ||
         urlError();
       if (this.isNew()) return base;
       var id = this.get(this.idAttribute);
       return base.replace(/[^\/]$/, '$&/') + encodeURIComponent(id);
     },
 
     // **parse** converts a response into the hash of attributes to be `set` on
     // the model. The default implementation is just to pass the response along.
     parse: function(resp, options) {
       return resp;
     },
 
     // Create a new model with identical attributes to this one.
     clone: function() {
       return new this.constructor(this.attributes);
     },
 
     // A model is new if it has never been saved to the server, and lacks an id.
     isNew: function() {
       return !this.has(this.idAttribute);
     },
 
     // Check if the model is currently in a valid state.
     isValid: function(options) {
       return this._validate({}, _.extend({}, options, {validate: true}));
     },
 
     // Run validation against the next complete set of model attributes,
     // returning `true` if all is well. Otherwise, fire an `"invalid"` event.
     _validate: function(attrs, options) {
       if (!options.validate || !this.validate) return true;
       attrs = _.extend({}, this.attributes, attrs);
       var error = this.validationError = this.validate(attrs, options) || null;
       if (!error) return true;
       this.trigger('invalid', this, error, _.extend(options, {validationError: error}));
       return false;
     }
 
   });
 
   // Backbone.Collection
   // -------------------
 
   // If models tend to represent a single row of data, a Backbone Collection is
   // more analogous to a table full of data ... or a small slice or page of that
   // table, or a collection of rows that belong together for a particular reason
   // -- all of the messages in this particular folder, all of the documents
   // belonging to this particular author, and so on. Collections maintain
   // indexes of their models, both in order, and for lookup by `id`.
 
   // Create a new **Collection**, perhaps to contain a specific type of `model`.
   // If a `comparator` is specified, the Collection will maintain
   // its models in sort order, as they're added and removed.
   var Collection = Backbone.Collection = function(models, options) {
     options || (options = {});
     this.preinitialize.apply(this, arguments);
     if (options.model) this.model = options.model;
     if (options.comparator !== void 0) this.comparator = options.comparator;
     this._reset();
     this.initialize.apply(this, arguments);
     if (models) this.reset(models, _.extend({silent: true}, options));
   };
 
   // Default options for `Collection#set`.
   var setOptions = {add: true, remove: true, merge: true};
   var addOptions = {add: true, remove: false};
 
   // Splices `insert` into `array` at index `at`.
   var splice = function(array, insert, at) {
     at = Math.min(Math.max(at, 0), array.length);
     var tail = Array(array.length - at);
     var length = insert.length;
     var i;
     for (i = 0; i < tail.length; i++) tail[i] = array[i + at];
     for (i = 0; i < length; i++) array[i + at] = insert[i];
     for (i = 0; i < tail.length; i++) array[i + length + at] = tail[i];
   };
 
   // Define the Collection's inheritable methods.
   _.extend(Collection.prototype, Events, {
 
     // The default model for a collection is just a **Backbone.Model**.
     // This should be overridden in most cases.
     model: Model,
 
 
     // preinitialize is an empty function by default. You can override it with a function
     // or object.  preinitialize will run before any instantiation logic is run in the Collection.
     preinitialize: function(){},
 
     // Initialize is an empty function by default. Override it with your own
     // initialization logic.
     initialize: function(){},
 
     // The JSON representation of a Collection is an array of the
     // models' attributes.
     toJSON: function(options) {
       return this.map(function(model) { return model.toJSON(options); });
     },
 
     // Proxy `Backbone.sync` by default.
     sync: function() {
       return Backbone.sync.apply(this, arguments);
     },
 
     // Add a model, or list of models to the set. `models` may be Backbone
     // Models or raw JavaScript objects to be converted to Models, or any
     // combination of the two.
     add: function(models, options) {
       return this.set(models, _.extend({merge: false}, options, addOptions));
     },
 
     // Remove a model, or a list of models from the set.
     remove: function(models, options) {
       options = _.extend({}, options);
       var singular = !_.isArray(models);
       models = singular ? [models] : models.slice();
       var removed = this._removeModels(models, options);
       if (!options.silent && removed.length) {
         options.changes = {added: [], merged: [], removed: removed};
         this.trigger('update', this, options);
       }
       return singular ? removed[0] : removed;
     },
 
     // Update a collection by `set`-ing a new list of models, adding new ones,
     // removing models that are no longer present, and merging models that
     // already exist in the collection, as necessary. Similar to **Model#set**,
     // the core operation for updating the data contained by the collection.
     set: function(models, options) {
       if (models == null) return;
 
       options = _.extend({}, setOptions, options);
       if (options.parse && !this._isModel(models)) {
         models = this.parse(models, options) || [];
       }
 
       var singular = !_.isArray(models);
       models = singular ? [models] : models.slice();
 
       var at = options.at;
       if (at != null) at = +at;
       if (at > this.length) at = this.length;
       if (at < 0) at += this.length + 1;
 
       var set = [];
       var toAdd = [];
       var toMerge = [];
       var toRemove = [];
       var modelMap = {};
 
       var add = options.add;
       var merge = options.merge;
       var remove = options.remove;
 
       var sort = false;
       var sortable = this.comparator && at == null && options.sort !== false;
       var sortAttr = _.isString(this.comparator) ? this.comparator : null;
 
       // Turn bare objects into model references, and prevent invalid models
       // from being added.
       var model, i;
       for (i = 0; i < models.length; i++) {
         model = models[i];
 
         // If a duplicate is found, prevent it from being added and
         // optionally merge it into the existing model.
         var existing = this.get(model);
         if (existing) {
           if (merge && model !== existing) {
             var attrs = this._isModel(model) ? model.attributes : model;
             if (options.parse) attrs = existing.parse(attrs, options);
             existing.set(attrs, options);
             toMerge.push(existing);
             if (sortable && !sort) sort = existing.hasChanged(sortAttr);
           }
           if (!modelMap[existing.cid]) {
             modelMap[existing.cid] = true;
             set.push(existing);
           }
           models[i] = existing;
 
         // If this is a new, valid model, push it to the `toAdd` list.
         } else if (add) {
           model = models[i] = this._prepareModel(model, options);
           if (model) {
             toAdd.push(model);
             this._addReference(model, options);
             modelMap[model.cid] = true;
             set.push(model);
           }
         }
       }
 
       // Remove stale models.
       if (remove) {
         for (i = 0; i < this.length; i++) {
           model = this.models[i];
           if (!modelMap[model.cid]) toRemove.push(model);
         }
         if (toRemove.length) this._removeModels(toRemove, options);
       }
 
       // See if sorting is needed, update `length` and splice in new models.
       var orderChanged = false;
       var replace = !sortable && add && remove;
       if (set.length && replace) {
         orderChanged = this.length !== set.length || _.some(this.models, function(m, index) {
           return m !== set[index];
         });
         this.models.length = 0;
         splice(this.models, set, 0);
         this.length = this.models.length;
       } else if (toAdd.length) {
         if (sortable) sort = true;
         splice(this.models, toAdd, at == null ? this.length : at);
         this.length = this.models.length;
       }
 
       // Silently sort the collection if appropriate.
       if (sort) this.sort({silent: true});
 
       // Unless silenced, it's time to fire all appropriate add/sort/update events.
       if (!options.silent) {
         for (i = 0; i < toAdd.length; i++) {
           if (at != null) options.index = at + i;
           model = toAdd[i];
           model.trigger('add', model, this, options);
         }
         if (sort || orderChanged) this.trigger('sort', this, options);
         if (toAdd.length || toRemove.length || toMerge.length) {
           options.changes = {
             added: toAdd,
             removed: toRemove,
             merged: toMerge
           };
           this.trigger('update', this, options);
         }
       }
 
       // Return the added (or merged) model (or models).
       return singular ? models[0] : models;
     },
 
     // When you have more items than you want to add or remove individually,
     // you can reset the entire set with a new list of models, without firing
     // any granular `add` or `remove` events. Fires `reset` when finished.
     // Useful for bulk operations and optimizations.
     reset: function(models, options) {
       options = options ? _.clone(options) : {};
       for (var i = 0; i < this.models.length; i++) {
         this._removeReference(this.models[i], options);
       }
       options.previousModels = this.models;
       this._reset();
       models = this.add(models, _.extend({silent: true}, options));
       if (!options.silent) this.trigger('reset', this, options);
       return models;
     },
 
     // Add a model to the end of the collection.
     push: function(model, options) {
       return this.add(model, _.extend({at: this.length}, options));
     },
 
     // Remove a model from the end of the collection.
     pop: function(options) {
       var model = this.at(this.length - 1);
       return this.remove(model, options);
     },
 
     // Add a model to the beginning of the collection.
     unshift: function(model, options) {
       return this.add(model, _.extend({at: 0}, options));
     },
 
     // Remove a model from the beginning of the collection.
     shift: function(options) {
       var model = this.at(0);
       return this.remove(model, options);
     },
 
     // Slice out a sub-array of models from the collection.
     slice: function() {
       return slice.apply(this.models, arguments);
     },
 
     // Get a model from the set by id, cid, model object with id or cid
     // properties, or an attributes object that is transformed through modelId.
     get: function(obj) {
       if (obj == null) return void 0;
       return this._byId[obj] ||
         this._byId[this.modelId(this._isModel(obj) ? obj.attributes : obj)] ||
         obj.cid && this._byId[obj.cid];
     },
 
     // Returns `true` if the model is in the collection.
     has: function(obj) {
       return this.get(obj) != null;
     },
 
     // Get the model at the given index.
     at: function(index) {
       if (index < 0) index += this.length;
       return this.models[index];
     },
 
     // Return models with matching attributes. Useful for simple cases of
     // `filter`.
     where: function(attrs, first) {
       return this[first ? 'find' : 'filter'](attrs);
     },
 
     // Return the first model with matching attributes. Useful for simple cases
     // of `find`.
     findWhere: function(attrs) {
       return this.where(attrs, true);
     },
 
     // Force the collection to re-sort itself. You don't need to call this under
     // normal circumstances, as the set will maintain sort order as each item
     // is added.
     sort: function(options) {
       var comparator = this.comparator;
       if (!comparator) throw new Error('Cannot sort a set without a comparator');
       options || (options = {});
 
       var length = comparator.length;
       if (_.isFunction(comparator)) comparator = comparator.bind(this);
 
       // Run sort based on type of `comparator`.
       if (length === 1 || _.isString(comparator)) {
         this.models = this.sortBy(comparator);
       } else {
         this.models.sort(comparator);
       }
       if (!options.silent) this.trigger('sort', this, options);
       return this;
     },
 
     // Pluck an attribute from each model in the collection.
     pluck: function(attr) {
       return this.map(attr + '');
     },
 
     // Fetch the default set of models for this collection, resetting the
     // collection when they arrive. If `reset: true` is passed, the response
     // data will be passed through the `reset` method instead of `set`.
     fetch: function(options) {
       options = _.extend({parse: true}, options);
       var success = options.success;
       var collection = this;
       options.success = function(resp) {
         var method = options.reset ? 'reset' : 'set';
         collection[method](resp, options);
         if (success) success.call(options.context, collection, resp, options);
         collection.trigger('sync', collection, resp, options);
       };
       wrapError(this, options);
       return this.sync('read', this, options);
     },
 
     // Create a new instance of a model in this collection. Add the model to the
     // collection immediately, unless `wait: true` is passed, in which case we
     // wait for the server to agree.
     create: function(model, options) {
       options = options ? _.clone(options) : {};
       var wait = options.wait;
       model = this._prepareModel(model, options);
       if (!model) return false;
       if (!wait) this.add(model, options);
       var collection = this;
       var success = options.success;
       options.success = function(m, resp, callbackOpts) {
         if (wait) collection.add(m, callbackOpts);
         if (success) success.call(callbackOpts.context, m, resp, callbackOpts);
       };
       model.save(null, options);
       return model;
     },
 
     // **parse** converts a response into a list of models to be added to the
     // collection. The default implementation is just to pass it through.
     parse: function(resp, options) {
       return resp;
     },
 
     // Create a new collection with an identical list of models as this one.
     clone: function() {
       return new this.constructor(this.models, {
         model: this.model,
         comparator: this.comparator
       });
     },
 
     // Define how to uniquely identify models in the collection.
     modelId: function(attrs) {
       return attrs[this.model.prototype.idAttribute || 'id'];
     },
 
     // Get an iterator of all models in this collection.
     values: function() {
       return new CollectionIterator(this, ITERATOR_VALUES);
     },
 
     // Get an iterator of all model IDs in this collection.
     keys: function() {
       return new CollectionIterator(this, ITERATOR_KEYS);
     },
 
     // Get an iterator of all [ID, model] tuples in this collection.
     entries: function() {
       return new CollectionIterator(this, ITERATOR_KEYSVALUES);
     },
 
     // Private method to reset all internal state. Called when the collection
     // is first initialized or reset.
     _reset: function() {
       this.length = 0;
       this.models = [];
       this._byId  = {};
     },
 
     // Prepare a hash of attributes (or other model) to be added to this
     // collection.
     _prepareModel: function(attrs, options) {
       if (this._isModel(attrs)) {
         if (!attrs.collection) attrs.collection = this;
         return attrs;
       }
       options = options ? _.clone(options) : {};
       options.collection = this;
       var model = new this.model(attrs, options);
       if (!model.validationError) return model;
       this.trigger('invalid', this, model.validationError, options);
       return false;
     },
 
     // Internal method called by both remove and set.
     _removeModels: function(models, options) {
       var removed = [];
       for (var i = 0; i < models.length; i++) {
         var model = this.get(models[i]);
         if (!model) continue;
 
         var index = this.indexOf(model);
         this.models.splice(index, 1);
         this.length--;
 
         // Remove references before triggering 'remove' event to prevent an
         // infinite loop. #3693
         delete this._byId[model.cid];
         var id = this.modelId(model.attributes);
         if (id != null) delete this._byId[id];
 
         if (!options.silent) {
           options.index = index;
           model.trigger('remove', model, this, options);
         }
 
         removed.push(model);
         this._removeReference(model, options);
       }
       return removed;
     },
 
     // Method for checking whether an object should be considered a model for
     // the purposes of adding to the collection.
     _isModel: function(model) {
       return model instanceof Model;
     },
 
     // Internal method to create a model's ties to a collection.
     _addReference: function(model, options) {
       this._byId[model.cid] = model;
       var id = this.modelId(model.attributes);
       if (id != null) this._byId[id] = model;
       model.on('all', this._onModelEvent, this);
     },
 
     // Internal method to sever a model's ties to a collection.
     _removeReference: function(model, options) {
       delete this._byId[model.cid];
       var id = this.modelId(model.attributes);
       if (id != null) delete this._byId[id];
       if (this === model.collection) delete model.collection;
       model.off('all', this._onModelEvent, this);
     },
 
     // Internal method called every time a model in the set fires an event.
     // Sets need to update their indexes when models change ids. All other
     // events simply proxy through. "add" and "remove" events that originate
     // in other collections are ignored.
     _onModelEvent: function(event, model, collection, options) {
       if (model) {
         if ((event === 'add' || event === 'remove') && collection !== this) return;
         if (event === 'destroy') this.remove(model, options);
         if (event === 'change') {
           var prevId = this.modelId(model.previousAttributes());
           var id = this.modelId(model.attributes);
           if (prevId !== id) {
             if (prevId != null) delete this._byId[prevId];
             if (id != null) this._byId[id] = model;
           }
         }
       }
       this.trigger.apply(this, arguments);
     }
 
   });
 
   // Defining an @@iterator method implements JavaScript's Iterable protocol.
   // In modern ES2015 browsers, this value is found at Symbol.iterator.
   /* global Symbol */
   var $$iterator = typeof Symbol === 'function' && Symbol.iterator;
   if ($$iterator) {
     Collection.prototype[$$iterator] = Collection.prototype.values;
   }
 
   // CollectionIterator
   // ------------------
 
   // A CollectionIterator implements JavaScript's Iterator protocol, allowing the
   // use of `for of` loops in modern browsers and interoperation between
   // Backbone.Collection and other JavaScript functions and third-party libraries
   // which can operate on Iterables.
   var CollectionIterator = function(collection, kind) {
     this._collection = collection;
     this._kind = kind;
     this._index = 0;
   };
 
   // This "enum" defines the three possible kinds of values which can be emitted
   // by a CollectionIterator that correspond to the values(), keys() and entries()
   // methods on Collection, respectively.
   var ITERATOR_VALUES = 1;
   var ITERATOR_KEYS = 2;
   var ITERATOR_KEYSVALUES = 3;
 
   // All Iterators should themselves be Iterable.
   if ($$iterator) {
     CollectionIterator.prototype[$$iterator] = function() {
       return this;
     };
   }
 
   CollectionIterator.prototype.next = function() {
     if (this._collection) {
 
       // Only continue iterating if the iterated collection is long enough.
       if (this._index < this._collection.length) {
         var model = this._collection.at(this._index);
         this._index++;
 
         // Construct a value depending on what kind of values should be iterated.
         var value;
         if (this._kind === ITERATOR_VALUES) {
           value = model;
         } else {
           var id = this._collection.modelId(model.attributes);
           if (this._kind === ITERATOR_KEYS) {
             value = id;
           } else { // ITERATOR_KEYSVALUES
             value = [id, model];
           }
         }
         return {value: value, done: false};
       }
 
       // Once exhausted, remove the reference to the collection so future
       // calls to the next method always return done.
       this._collection = void 0;
     }
 
     return {value: void 0, done: true};
   };
 
   // Backbone.View
   // -------------
 
   // Backbone Views are almost more convention than they are actual code. A View
   // is simply a JavaScript object that represents a logical chunk of UI in the
   // DOM. This might be a single item, an entire list, a sidebar or panel, or
   // even the surrounding frame which wraps your whole app. Defining a chunk of
   // UI as a **View** allows you to define your DOM events declaratively, without
   // having to worry about render order ... and makes it easy for the view to
   // react to specific changes in the state of your models.
 
   // Creating a Backbone.View creates its initial element outside of the DOM,
   // if an existing element is not provided...
   var View = Backbone.View = function(options) {
     this.cid = _.uniqueId('view');
     this.preinitialize.apply(this, arguments);
     _.extend(this, _.pick(options, viewOptions));
     this._ensureElement();
     this.initialize.apply(this, arguments);
   };
 
   // Cached regex to split keys for `delegate`.
   var delegateEventSplitter = /^(\S+)\s*(.*)$/;
 
   // List of view options to be set as properties.
   var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName', 'events'];
 
   // Set up all inheritable **Backbone.View** properties and methods.
   _.extend(View.prototype, Events, {
 
     // The default `tagName` of a View's element is `"div"`.
     tagName: 'div',
 
     // jQuery delegate for element lookup, scoped to DOM elements within the
     // current view. This should be preferred to global lookups where possible.
     $: function(selector) {
       return this.$el.find(selector);
     },
 
     // preinitialize is an empty function by default. You can override it with a function
     // or object.  preinitialize will run before any instantiation logic is run in the View
     preinitialize: function(){},
 
     // Initialize is an empty function by default. Override it with your own
     // initialization logic.
     initialize: function(){},
 
     // **render** is the core function that your view should override, in order
     // to populate its element (`this.el`), with the appropriate HTML. The
     // convention is for **render** to always return `this`.
     render: function() {
       return this;
     },
 
     // Remove this view by taking the element out of the DOM, and removing any
     // applicable Backbone.Events listeners.
     remove: function() {
       this._removeElement();
       this.stopListening();
       return this;
     },
 
     // Remove this view's element from the document and all event listeners
     // attached to it. Exposed for subclasses using an alternative DOM
     // manipulation API.
     _removeElement: function() {
       this.$el.remove();
     },
 
     // Change the view's element (`this.el` property) and re-delegate the
     // view's events on the new element.
     setElement: function(element) {
       this.undelegateEvents();
       this._setElement(element);
       this.delegateEvents();
       return this;
     },
 
     // Creates the `this.el` and `this.$el` references for this view using the
     // given `el`. `el` can be a CSS selector or an HTML string, a jQuery
     // context or an element. Subclasses can override this to utilize an
     // alternative DOM manipulation API and are only required to set the
     // `this.el` property.
     _setElement: function(el) {
       this.$el = el instanceof Backbone.$ ? el : Backbone.$(el);
       this.el = this.$el[0];
     },
 
     // Set callbacks, where `this.events` is a hash of
     //
     // *{"event selector": "callback"}*
     //
     //     {
     //       'mousedown .title':  'edit',
     //       'click .button':     'save',
     //       'click .open':       function(e) { ... }
     //     }
     //
     // pairs. Callbacks will be bound to the view, with `this` set properly.
     // Uses event delegation for efficiency.
     // Omitting the selector binds the event to `this.el`.
     delegateEvents: function(events) {
       events || (events = _.result(this, 'events'));
       if (!events) return this;
       this.undelegateEvents();
       for (var key in events) {
         var method = events[key];
         if (!_.isFunction(method)) method = this[method];
         if (!method) continue;
         var match = key.match(delegateEventSplitter);
         this.delegate(match[1], match[2], method.bind(this));
       }
       return this;
     },
 
     // Add a single event listener to the view's element (or a child element
     // using `selector`). This only works for delegate-able events: not `focus`,
     // `blur`, and not `change`, `submit`, and `reset` in Internet Explorer.
     delegate: function(eventName, selector, listener) {
       this.$el.on(eventName + '.delegateEvents' + this.cid, selector, listener);
       return this;
     },
 
     // Clears all callbacks previously bound to the view by `delegateEvents`.
     // You usually don't need to use this, but may wish to if you have multiple
     // Backbone views attached to the same DOM element.
     undelegateEvents: function() {
       if (this.$el) this.$el.off('.delegateEvents' + this.cid);
       return this;
     },
 
     // A finer-grained `undelegateEvents` for removing a single delegated event.
     // `selector` and `listener` are both optional.
     undelegate: function(eventName, selector, listener) {
       this.$el.off(eventName + '.delegateEvents' + this.cid, selector, listener);
       return this;
     },
 
     // Produces a DOM element to be assigned to your view. Exposed for
     // subclasses using an alternative DOM manipulation API.
     _createElement: function(tagName) {
       return document.createElement(tagName);
     },
 
     // Ensure that the View has a DOM element to render into.
     // If `this.el` is a string, pass it through `$()`, take the first
     // matching element, and re-assign it to `el`. Otherwise, create
     // an element from the `id`, `className` and `tagName` properties.
     _ensureElement: function() {
       if (!this.el) {
         var attrs = _.extend({}, _.result(this, 'attributes'));
         if (this.id) attrs.id = _.result(this, 'id');
         if (this.className) attrs['class'] = _.result(this, 'className');
         this.setElement(this._createElement(_.result(this, 'tagName')));
         this._setAttributes(attrs);
       } else {
         this.setElement(_.result(this, 'el'));
       }
     },
 
     // Set attributes from a hash on this view's element.  Exposed for
     // subclasses using an alternative DOM manipulation API.
     _setAttributes: function(attributes) {
       this.$el.attr(attributes);
     }
 
   });
 
   // Proxy Backbone class methods to Underscore functions, wrapping the model's
   // `attributes` object or collection's `models` array behind the scenes.
   //
   // collection.filter(function(model) { return model.get('age') > 10 });
   // collection.each(this.addView);
   //
   // `Function#apply` can be slow so we use the method's arg count, if we know it.
   var addMethod = function(base, length, method, attribute) {
     switch (length) {
       case 1: return function() {
         return base[method](this[attribute]);
       };
       case 2: return function(value) {
         return base[method](this[attribute], value);
       };
       case 3: return function(iteratee, context) {
         return base[method](this[attribute], cb(iteratee, this), context);
       };
       case 4: return function(iteratee, defaultVal, context) {
         return base[method](this[attribute], cb(iteratee, this), defaultVal, context);
       };
       default: return function() {
         var args = slice.call(arguments);
         args.unshift(this[attribute]);
         return base[method].apply(base, args);
       };
     }
   };
 
   var addUnderscoreMethods = function(Class, base, methods, attribute) {
     _.each(methods, function(length, method) {
       if (base[method]) Class.prototype[method] = addMethod(base, length, method, attribute);
     });
   };
 
   // Support `collection.sortBy('attr')` and `collection.findWhere({id: 1})`.
   var cb = function(iteratee, instance) {
     if (_.isFunction(iteratee)) return iteratee;
     if (_.isObject(iteratee) && !instance._isModel(iteratee)) return modelMatcher(iteratee);
     if (_.isString(iteratee)) return function(model) { return model.get(iteratee); };
     return iteratee;
   };
   var modelMatcher = function(attrs) {
     var matcher = _.matches(attrs);
     return function(model) {
       return matcher(model.attributes);
     };
   };
 
   // Underscore methods that we want to implement on the Collection.
   // 90% of the core usefulness of Backbone Collections is actually implemented
   // right here:
   var collectionMethods = {forEach: 3, each: 3, map: 3, collect: 3, reduce: 0,
     foldl: 0, inject: 0, reduceRight: 0, foldr: 0, find: 3, detect: 3, filter: 3,
     select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 3, includes: 3,
     contains: 3, invoke: 0, max: 3, min: 3, toArray: 1, size: 1, first: 3,
     head: 3, take: 3, initial: 3, rest: 3, tail: 3, drop: 3, last: 3,
     without: 0, difference: 0, indexOf: 3, shuffle: 1, lastIndexOf: 3,
     isEmpty: 1, chain: 1, sample: 3, partition: 3, groupBy: 3, countBy: 3,
     sortBy: 3, indexBy: 3, findIndex: 3, findLastIndex: 3};
 
 
   // Underscore methods that we want to implement on the Model, mapped to the
   // number of arguments they take.
   var modelMethods = {keys: 1, values: 1, pairs: 1, invert: 1, pick: 0,
     omit: 0, chain: 1, isEmpty: 1};
 
   // Mix in each Underscore method as a proxy to `Collection#models`.
 
   _.each([
     [Collection, collectionMethods, 'models'],
     [Model, modelMethods, 'attributes']
   ], function(config) {
     var Base = config[0],
         methods = config[1],
         attribute = config[2];
 
     Base.mixin = function(obj) {
       var mappings = _.reduce(_.functions(obj), function(memo, name) {
         memo[name] = 0;
         return memo;
       }, {});
       addUnderscoreMethods(Base, obj, mappings, attribute);
     };
 
     addUnderscoreMethods(Base, _, methods, attribute);
   });
 
   // Backbone.sync
   // -------------
 
   // Override this function to change the manner in which Backbone persists
   // models to the server. You will be passed the type of request, and the
   // model in question. By default, makes a RESTful Ajax request
   // to the model's `url()`. Some possible customizations could be:
   //
   // * Use `setTimeout` to batch rapid-fire updates into a single request.
   // * Send up the models as XML instead of JSON.
   // * Persist models via WebSockets instead of Ajax.
   //
   // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
   // as `POST`, with a `_method` parameter containing the true HTTP method,
   // as well as all requests with the body as `application/x-www-form-urlencoded`
   // instead of `application/json` with the model in a param named `model`.
   // Useful when interfacing with server-side languages like **PHP** that make
   // it difficult to read the body of `PUT` requests.
   Backbone.sync = function(method, model, options) {
     var type = methodMap[method];
 
     // Default options, unless specified.
     _.defaults(options || (options = {}), {
       emulateHTTP: Backbone.emulateHTTP,
       emulateJSON: Backbone.emulateJSON
     });
 
     // Default JSON-request options.
     var params = {type: type, dataType: 'json'};
 
     // Ensure that we have a URL.
     if (!options.url) {
       params.url = _.result(model, 'url') || urlError();
     }
 
     // Ensure that we have the appropriate request data.
     if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
       params.contentType = 'application/json';
       params.data = JSON.stringify(options.attrs || model.toJSON(options));
     }
 
     // For older servers, emulate JSON by encoding the request into an HTML-form.
     if (options.emulateJSON) {
       params.contentType = 'application/x-www-form-urlencoded';
       params.data = params.data ? {model: params.data} : {};
     }
 
     // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
     // And an `X-HTTP-Method-Override` header.
     if (options.emulateHTTP && (type === 'PUT' || type === 'DELETE' || type === 'PATCH')) {
       params.type = 'POST';
       if (options.emulateJSON) params.data._method = type;
       var beforeSend = options.beforeSend;
       options.beforeSend = function(xhr) {
         xhr.setRequestHeader('X-HTTP-Method-Override', type);
         if (beforeSend) return beforeSend.apply(this, arguments);
       };
     }
 
     // Don't process data on a non-GET request.
     if (params.type !== 'GET' && !options.emulateJSON) {
       params.processData = false;
     }
 
     // Pass along `textStatus` and `errorThrown` from jQuery.
     var error = options.error;
     options.error = function(xhr, textStatus, errorThrown) {
       options.textStatus = textStatus;
       options.errorThrown = errorThrown;
       if (error) error.call(options.context, xhr, textStatus, errorThrown);
     };
 
     // Make the request, allowing the user to override any Ajax options.
     var xhr = options.xhr = Backbone.ajax(_.extend(params, options));
     model.trigger('request', model, xhr, options);
     return xhr;
   };
 
   // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
   var methodMap = {
     create: 'POST',
     update: 'PUT',
     patch: 'PATCH',
     delete: 'DELETE',
     read: 'GET'
   };
 
   // Set the default implementation of `Backbone.ajax` to proxy through to `$`.
   // Override this if you'd like to use a different library.
   Backbone.ajax = function() {
     return Backbone.$.ajax.apply(Backbone.$, arguments);
   };
 
   // Backbone.Router
   // ---------------
 
   // Routers map faux-URLs to actions, and fire events when routes are
   // matched. Creating a new one sets its `routes` hash, if not set statically.
   var Router = Backbone.Router = function(options) {
     options || (options = {});
     this.preinitialize.apply(this, arguments);
     if (options.routes) this.routes = options.routes;
     this._bindRoutes();
     this.initialize.apply(this, arguments);
   };
 
   // Cached regular expressions for matching named param parts and splatted
   // parts of route strings.
   var optionalParam = /\((.*?)\)/g;
   var namedParam    = /(\(\?)?:\w+/g;
   var splatParam    = /\*\w+/g;
   var escapeRegExp  = /[\-{}\[\]+?.,\\\^$|#\s]/g;
 
   // Set up all inheritable **Backbone.Router** properties and methods.
   _.extend(Router.prototype, Events, {
 
     // preinitialize is an empty function by default. You can override it with a function
     // or object.  preinitialize will run before any instantiation logic is run in the Router.
     preinitialize: function(){},
 
     // Initialize is an empty function by default. Override it with your own
     // initialization logic.
     initialize: function(){},
 
     // Manually bind a single named route to a callback. For example:
     //
     //     this.route('search/:query/p:num', 'search', function(query, num) {
     //       ...
     //     });
     //
     route: function(route, name, callback) {
       if (!_.isRegExp(route)) route = this._routeToRegExp(route);
       if (_.isFunction(name)) {
         callback = name;
         name = '';
       }
       if (!callback) callback = this[name];
       var router = this;
       Backbone.history.route(route, function(fragment) {
         var args = router._extractParameters(route, fragment);
         if (router.execute(callback, args, name) !== false) {
           router.trigger.apply(router, ['route:' + name].concat(args));
           router.trigger('route', name, args);
           Backbone.history.trigger('route', router, name, args);
         }
       });
       return this;
     },
 
     // Execute a route handler with the provided parameters.  This is an
     // excellent place to do pre-route setup or post-route cleanup.
     execute: function(callback, args, name) {
       if (callback) callback.apply(this, args);
     },
 
     // Simple proxy to `Backbone.history` to save a fragment into the history.
     navigate: function(fragment, options) {
       Backbone.history.navigate(fragment, options);
       return this;
     },
 
     // Bind all defined routes to `Backbone.history`. We have to reverse the
     // order of the routes here to support behavior where the most general
     // routes can be defined at the bottom of the route map.
     _bindRoutes: function() {
       if (!this.routes) return;
       this.routes = _.result(this, 'routes');
       var route, routes = _.keys(this.routes);
       while ((route = routes.pop()) != null) {
         this.route(route, this.routes[route]);
       }
     },
 
     // Convert a route string into a regular expression, suitable for matching
     // against the current location hash.
     _routeToRegExp: function(route) {
       route = route.replace(escapeRegExp, '\\$&')
         .replace(optionalParam, '(?:$1)?')
         .replace(namedParam, function(match, optional) {
           return optional ? match : '([^/?]+)';
         })
         .replace(splatParam, '([^?]*?)');
       return new RegExp('^' + route + '(?:\\?([\\s\\S]*))?$');
     },
 
     // Given a route, and a URL fragment that it matches, return the array of
     // extracted decoded parameters. Empty or unmatched parameters will be
     // treated as `null` to normalize cross-browser behavior.
     _extractParameters: function(route, fragment) {
       var params = route.exec(fragment).slice(1);
       return _.map(params, function(param, i) {
         // Don't decode the search params.
         if (i === params.length - 1) return param || null;
         return param ? decodeURIComponent(param) : null;
       });
     }
 
   });
 
   // Backbone.History
   // ----------------
 
   // Handles cross-browser history management, based on either
   // [pushState](http://diveintohtml5.info/history.html) and real URLs, or
   // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)
   // and URL fragments. If the browser supports neither (old IE, natch),
   // falls back to polling.
   var History = Backbone.History = function() {
     this.handlers = [];
     this.checkUrl = this.checkUrl.bind(this);
 
     // Ensure that `History` can be used outside of the browser.
     if (typeof window !== 'undefined') {
       this.location = window.location;
       this.history = window.history;
     }
   };
 
   // Cached regex for stripping a leading hash/slash and trailing space.
   var routeStripper = /^[#\/]|\s+$/g;
 
   // Cached regex for stripping leading and trailing slashes.
   var rootStripper = /^\/+|\/+$/g;
 
   // Cached regex for stripping urls of hash.
   var pathStripper = /#.*$/;
 
   // Has the history handling already been started?
   History.started = false;
 
   // Set up all inheritable **Backbone.History** properties and methods.
   _.extend(History.prototype, Events, {
 
     // The default interval to poll for hash changes, if necessary, is
     // twenty times a second.
     interval: 50,
 
     // Are we at the app root?
     atRoot: function() {
       var path = this.location.pathname.replace(/[^\/]$/, '$&/');
       return path === this.root && !this.getSearch();
     },
 
     // Does the pathname match the root?
     matchRoot: function() {
       var path = this.decodeFragment(this.location.pathname);
       var rootPath = path.slice(0, this.root.length - 1) + '/';
       return rootPath === this.root;
     },
 
     // Unicode characters in `location.pathname` are percent encoded so they're
     // decoded for comparison. `%25` should not be decoded since it may be part
     // of an encoded parameter.
     decodeFragment: function(fragment) {
       return decodeURI(fragment.replace(/%25/g, '%2525'));
     },
 
     // In IE6, the hash fragment and search params are incorrect if the
     // fragment contains `?`.
     getSearch: function() {
       var match = this.location.href.replace(/#.*/, '').match(/\?.+/);
       return match ? match[0] : '';
     },
 
     // Gets the true hash value. Cannot use location.hash directly due to bug
     // in Firefox where location.hash will always be decoded.
     getHash: function(window) {
       var match = (window || this).location.href.match(/#(.*)$/);
       return match ? match[1] : '';
     },
 
     // Get the pathname and search params, without the root.
     getPath: function() {
       var path = this.decodeFragment(
         this.location.pathname + this.getSearch()
       ).slice(this.root.length - 1);
       return path.charAt(0) === '/' ? path.slice(1) : path;
     },
 
     // Get the cross-browser normalized URL fragment from the path or hash.
     getFragment: function(fragment) {
       if (fragment == null) {
         if (this._usePushState || !this._wantsHashChange) {
           fragment = this.getPath();
         } else {
           fragment = this.getHash();
         }
       }
       return fragment.replace(routeStripper, '');
     },
 
     // Start the hash change handling, returning `true` if the current URL matches
     // an existing route, and `false` otherwise.
     start: function(options) {
       if (History.started) throw new Error('Backbone.history has already been started');
       History.started = true;
 
       // Figure out the initial configuration. Do we need an iframe?
       // Is pushState desired ... is it available?
       this.options          = _.extend({root: '/'}, this.options, options);
       this.root             = this.options.root;
       this._wantsHashChange = this.options.hashChange !== false;
       this._hasHashChange   = 'onhashchange' in window && (document.documentMode === void 0 || document.documentMode > 7);
       this._useHashChange   = this._wantsHashChange && this._hasHashChange;
       this._wantsPushState  = !!this.options.pushState;
       this._hasPushState    = !!(this.history && this.history.pushState);
       this._usePushState    = this._wantsPushState && this._hasPushState;
       this.fragment         = this.getFragment();
 
       // Normalize root to always include a leading and trailing slash.
       this.root = ('/' + this.root + '/').replace(rootStripper, '/');
 
       // Transition from hashChange to pushState or vice versa if both are
       // requested.
       if (this._wantsHashChange && this._wantsPushState) {
 
         // If we've started off with a route from a `pushState`-enabled
         // browser, but we're currently in a browser that doesn't support it...
         if (!this._hasPushState && !this.atRoot()) {
           var rootPath = this.root.slice(0, -1) || '/';
           this.location.replace(rootPath + '#' + this.getPath());
           // Return immediately as browser will do redirect to new url
           return true;
 
         // Or if we've started out with a hash-based route, but we're currently
         // in a browser where it could be `pushState`-based instead...
         } else if (this._hasPushState && this.atRoot()) {
           this.navigate(this.getHash(), {replace: true});
         }
 
       }
 
       // Proxy an iframe to handle location events if the browser doesn't
       // support the `hashchange` event, HTML5 history, or the user wants
       // `hashChange` but not `pushState`.
       if (!this._hasHashChange && this._wantsHashChange && !this._usePushState) {
         this.iframe = document.createElement('iframe');
         this.iframe.src = 'javascript:0';
         this.iframe.style.display = 'none';
         this.iframe.tabIndex = -1;
         var body = document.body;
         // Using `appendChild` will throw on IE < 9 if the document is not ready.
         var iWindow = body.insertBefore(this.iframe, body.firstChild).contentWindow;
         iWindow.document.open();
         iWindow.document.close();
         iWindow.location.hash = '#' + this.fragment;
       }
 
       // Add a cross-platform `addEventListener` shim for older browsers.
       var addEventListener = window.addEventListener || function(eventName, listener) {
         return attachEvent('on' + eventName, listener);
       };
 
       // Depending on whether we're using pushState or hashes, and whether
       // 'onhashchange' is supported, determine how we check the URL state.
       if (this._usePushState) {
         addEventListener('popstate', this.checkUrl, false);
       } else if (this._useHashChange && !this.iframe) {
         addEventListener('hashchange', this.checkUrl, false);
       } else if (this._wantsHashChange) {
         this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
       }
 
       if (!this.options.silent) return this.loadUrl();
     },
 
     // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
     // but possibly useful for unit testing Routers.
     stop: function() {
       // Add a cross-platform `removeEventListener` shim for older browsers.
       var removeEventListener = window.removeEventListener || function(eventName, listener) {
         return detachEvent('on' + eventName, listener);
       };
 
       // Remove window listeners.
       if (this._usePushState) {
         removeEventListener('popstate', this.checkUrl, false);
       } else if (this._useHashChange && !this.iframe) {
         removeEventListener('hashchange', this.checkUrl, false);
       }
 
       // Clean up the iframe if necessary.
       if (this.iframe) {
         document.body.removeChild(this.iframe);
         this.iframe = null;
       }
 
       // Some environments will throw when clearing an undefined interval.
       if (this._checkUrlInterval) clearInterval(this._checkUrlInterval);
       History.started = false;
     },
 
     // Add a route to be tested when the fragment changes. Routes added later
     // may override previous routes.
     route: function(route, callback) {
       this.handlers.unshift({route: route, callback: callback});
     },
 
     // Checks the current URL to see if it has changed, and if it has,
     // calls `loadUrl`, normalizing across the hidden iframe.
     checkUrl: function(e) {
       var current = this.getFragment();
 
       // If the user pressed the back button, the iframe's hash will have
       // changed and we should use that for comparison.
       if (current === this.fragment && this.iframe) {
         current = this.getHash(this.iframe.contentWindow);
       }
 
       if (current === this.fragment) return false;
       if (this.iframe) this.navigate(current);
       this.loadUrl();
     },
 
     // Attempt to load the current URL fragment. If a route succeeds with a
     // match, returns `true`. If no defined routes matches the fragment,
     // returns `false`.
     loadUrl: function(fragment) {
       // If the root doesn't match, no routes can match either.
       if (!this.matchRoot()) return false;
       fragment = this.fragment = this.getFragment(fragment);
       return _.some(this.handlers, function(handler) {
         if (handler.route.test(fragment)) {
           handler.callback(fragment);
           return true;
         }
       });
     },
 
     // Save a fragment into the hash history, or replace the URL state if the
     // 'replace' option is passed. You are responsible for properly URL-encoding
     // the fragment in advance.
     //
     // The options object can contain `trigger: true` if you wish to have the
     // route callback be fired (not usually desirable), or `replace: true`, if
     // you wish to modify the current URL without adding an entry to the history.
     navigate: function(fragment, options) {
       if (!History.started) return false;
       if (!options || options === true) options = {trigger: !!options};
 
       // Normalize the fragment.
       fragment = this.getFragment(fragment || '');
 
       // Don't include a trailing slash on the root.
       var rootPath = this.root;
       if (fragment === '' || fragment.charAt(0) === '?') {
         rootPath = rootPath.slice(0, -1) || '/';
       }
       var url = rootPath + fragment;
 
       // Strip the fragment of the query and hash for matching.
       fragment = fragment.replace(pathStripper, '');
 
       // Decode for matching.
       var decodedFragment = this.decodeFragment(fragment);
 
       if (this.fragment === decodedFragment) return;
       this.fragment = decodedFragment;
 
       // If pushState is available, we use it to set the fragment as a real URL.
       if (this._usePushState) {
         this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);
 
       // If hash changes haven't been explicitly disabled, update the hash
       // fragment to store history.
       } else if (this._wantsHashChange) {
         this._updateHash(this.location, fragment, options.replace);
         if (this.iframe && fragment !== this.getHash(this.iframe.contentWindow)) {
           var iWindow = this.iframe.contentWindow;
 
           // Opening and closing the iframe tricks IE7 and earlier to push a
           // history entry on hash-tag change.  When replace is true, we don't
           // want this.
           if (!options.replace) {
             iWindow.document.open();
             iWindow.document.close();
           }
 
           this._updateHash(iWindow.location, fragment, options.replace);
         }
 
       // If you've told us that you explicitly don't want fallback hashchange-
       // based history, then `navigate` becomes a page refresh.
       } else {
         return this.location.assign(url);
       }
       if (options.trigger) return this.loadUrl(fragment);
     },
 
     // Update the hash location, either replacing the current entry, or adding
     // a new one to the browser history.
     _updateHash: function(location, fragment, replace) {
       if (replace) {
         var href = location.href.replace(/(javascript:|#).*$/, '');
         location.replace(href + '#' + fragment);
       } else {
         // Some browsers require that `hash` contains a leading #.
         location.hash = '#' + fragment;
       }
     }
 
   });
 
   // Create the default Backbone.history.
   Backbone.history = new History;
 
   // Helpers
   // -------
 
   // Helper function to correctly set up the prototype chain for subclasses.
   // Similar to `goog.inherits`, but uses a hash of prototype properties and
   // class properties to be extended.
   var extend = function(protoProps, staticProps) {
     var parent = this;
     var child;
 
     // The constructor function for the new subclass is either defined by you
     // (the "constructor" property in your `extend` definition), or defaulted
     // by us to simply call the parent constructor.
     if (protoProps && _.has(protoProps, 'constructor')) {
       child = protoProps.constructor;
     } else {
       child = function(){ return parent.apply(this, arguments); };
     }
 
     // Add static properties to the constructor function, if supplied.
     _.extend(child, parent, staticProps);
 
     // Set the prototype chain to inherit from `parent`, without calling
     // `parent`'s constructor function and add the prototype properties.
     child.prototype = _.create(parent.prototype, protoProps);
     child.prototype.constructor = child;
 
     // Set a convenience property in case the parent's prototype is needed
     // later.
     child.__super__ = parent.prototype;
 
     return child;
   };
 
   // Set up inheritance for the model, collection, router, view and history.
   Model.extend = Collection.extend = Router.extend = View.extend = History.extend = extend;
 
   // Throw an error when a URL is needed, and none is supplied.
   var urlError = function() {
     throw new Error('A "url" property or function must be specified');
   };
 
   // Wrap an optional error callback with a fallback error event.
   var wrapError = function(model, options) {
     var error = options.error;
     options.error = function(resp) {
       if (error) error.call(options.context, model, resp, options);
       model.trigger('error', model, resp, options);
     };
   };
 
   return Backbone;
 });