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   1  //     Backbone.js 1.6.0
   2  
   3  //     (c) 2010-2024 Jeremy Ashkenas and DocumentCloud
   4  //     Backbone may be freely distributed under the MIT license.
   5  //     For all details and documentation:
   6  //     http://backbonejs.org
   7  
   8  (function(factory) {
   9  
  10    // Establish the root object, `window` (`self`) in the browser, or `global` on the server.
  11    // We use `self` instead of `window` for `WebWorker` support.
  12    var root = typeof self == 'object' && self.self === self && self ||
  13              typeof global == 'object' && global.global === global && global;
  14  
  15    // Set up Backbone appropriately for the environment. Start with AMD.
  16    if (typeof define === 'function' && define.amd) {
  17      define(['underscore', 'jquery', 'exports'], function(_, $, exports) {
  18        // Export global even in AMD case in case this script is loaded with
  19        // others that may still expect a global Backbone.
  20        root.Backbone = factory(root, exports, _, $);
  21      });
  22  
  23    // Next for Node.js or CommonJS. jQuery may not be needed as a module.
  24    } else if (typeof exports !== 'undefined') {
  25      var _ = require('underscore'), $;
  26      try { $ = require('jquery'); } catch (e) {}
  27      factory(root, exports, _, $);
  28  
  29    // Finally, as a browser global.
  30    } else {
  31      root.Backbone = factory(root, {}, root._, root.jQuery || root.Zepto || root.ender || root.$);
  32    }
  33  
  34  })(function(root, Backbone, _, $) {
  35  
  36    // Initial Setup
  37    // -------------
  38  
  39    // Save the previous value of the `Backbone` variable, so that it can be
  40    // restored later on, if `noConflict` is used.
  41    var previousBackbone = root.Backbone;
  42  
  43    // Create a local reference to a common array method we'll want to use later.
  44    var slice = Array.prototype.slice;
  45  
  46    // Current version of the library. Keep in sync with `package.json`.
  47    Backbone.VERSION = '1.6.0';
  48  
  49    // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns
  50    // the `$` variable.
  51    Backbone.$ = $;
  52  
  53    // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
  54    // to its previous owner. Returns a reference to this Backbone object.
  55    Backbone.noConflict = function() {
  56      root.Backbone = previousBackbone;
  57      return this;
  58    };
  59  
  60    // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option
  61    // will fake `"PATCH"`, `"PUT"` and `"DELETE"` requests via the `_method` parameter and
  62    // set a `X-Http-Method-Override` header.
  63    Backbone.emulateHTTP = false;
  64  
  65    // Turn on `emulateJSON` to support legacy servers that can't deal with direct
  66    // `application/json` requests ... this will encode the body as
  67    // `application/x-www-form-urlencoded` instead and will send the model in a
  68    // form param named `model`.
  69    Backbone.emulateJSON = false;
  70  
  71    // Backbone.Events
  72    // ---------------
  73  
  74    // A module that can be mixed in to *any object* in order to provide it with
  75    // a custom event channel. You may bind a callback to an event with `on` or
  76    // remove with `off`; `trigger`-ing an event fires all callbacks in
  77    // succession.
  78    //
  79    //     var object = {};
  80    //     _.extend(object, Backbone.Events);
  81    //     object.on('expand', function(){ alert('expanded'); });
  82    //     object.trigger('expand');
  83    //
  84    var Events = Backbone.Events = {};
  85  
  86    // Regular expression used to split event strings.
  87    var eventSplitter = /\s+/;
  88  
  89    // A private global variable to share between listeners and listenees.
  90    var _listening;
  91  
  92    // Iterates over the standard `event, callback` (as well as the fancy multiple
  93    // space-separated events `"change blur", callback` and jQuery-style event
  94    // maps `{event: callback}`).
  95    var eventsApi = function(iteratee, events, name, callback, opts) {
  96      var i = 0, names;
  97      if (name && typeof name === 'object') {
  98        // Handle event maps.
  99        if (callback !== void 0 && 'context' in opts && opts.context === void 0) opts.context = callback;
 100        for (names = _.keys(name); i < names.length ; i++) {
 101          events = eventsApi(iteratee, events, names[i], name[names[i]], opts);
 102        }
 103      } else if (name && eventSplitter.test(name)) {
 104        // Handle space-separated event names by delegating them individually.
 105        for (names = name.split(eventSplitter); i < names.length; i++) {
 106          events = iteratee(events, names[i], callback, opts);
 107        }
 108      } else {
 109        // Finally, standard events.
 110        events = iteratee(events, name, callback, opts);
 111      }
 112      return events;
 113    };
 114  
 115    // Bind an event to a `callback` function. Passing `"all"` will bind
 116    // the callback to all events fired.
 117    Events.on = function(name, callback, context) {
 118      this._events = eventsApi(onApi, this._events || {}, name, callback, {
 119        context: context,
 120        ctx: this,
 121        listening: _listening
 122      });
 123  
 124      if (_listening) {
 125        var listeners = this._listeners || (this._listeners = {});
 126        listeners[_listening.id] = _listening;
 127        // Allow the listening to use a counter, instead of tracking
 128        // callbacks for library interop
 129        _listening.interop = false;
 130      }
 131  
 132      return this;
 133    };
 134  
 135    // Inversion-of-control versions of `on`. Tell *this* object to listen to
 136    // an event in another object... keeping track of what it's listening to
 137    // for easier unbinding later.
 138    Events.listenTo = function(obj, name, callback) {
 139      if (!obj) return this;
 140      var id = obj._listenId || (obj._listenId = _.uniqueId('l'));
 141      var listeningTo = this._listeningTo || (this._listeningTo = {});
 142      var listening = _listening = listeningTo[id];
 143  
 144      // This object is not listening to any other events on `obj` yet.
 145      // Setup the necessary references to track the listening callbacks.
 146      if (!listening) {
 147        this._listenId || (this._listenId = _.uniqueId('l'));
 148        listening = _listening = listeningTo[id] = new Listening(this, obj);
 149      }
 150  
 151      // Bind callbacks on obj.
 152      var error = tryCatchOn(obj, name, callback, this);
 153      _listening = void 0;
 154  
 155      if (error) throw error;
 156      // If the target obj is not Backbone.Events, track events manually.
 157      if (listening.interop) listening.on(name, callback);
 158  
 159      return this;
 160    };
 161  
 162    // The reducing API that adds a callback to the `events` object.
 163    var onApi = function(events, name, callback, options) {
 164      if (callback) {
 165        var handlers = events[name] || (events[name] = []);
 166        var context = options.context, ctx = options.ctx, listening = options.listening;
 167        if (listening) listening.count++;
 168  
 169        handlers.push({callback: callback, context: context, ctx: context || ctx, listening: listening});
 170      }
 171      return events;
 172    };
 173  
 174    // An try-catch guarded #on function, to prevent poisoning the global
 175    // `_listening` variable.
 176    var tryCatchOn = function(obj, name, callback, context) {
 177      try {
 178        obj.on(name, callback, context);
 179      } catch (e) {
 180        return e;
 181      }
 182    };
 183  
 184    // Remove one or many callbacks. If `context` is null, removes all
 185    // callbacks with that function. If `callback` is null, removes all
 186    // callbacks for the event. If `name` is null, removes all bound
 187    // callbacks for all events.
 188    Events.off = function(name, callback, context) {
 189      if (!this._events) return this;
 190      this._events = eventsApi(offApi, this._events, name, callback, {
 191        context: context,
 192        listeners: this._listeners
 193      });
 194  
 195      return this;
 196    };
 197  
 198    // Tell this object to stop listening to either specific events ... or
 199    // to every object it's currently listening to.
 200    Events.stopListening = function(obj, name, callback) {
 201      var listeningTo = this._listeningTo;
 202      if (!listeningTo) return this;
 203  
 204      var ids = obj ? [obj._listenId] : _.keys(listeningTo);
 205      for (var i = 0; i < ids.length; i++) {
 206        var listening = listeningTo[ids[i]];
 207  
 208        // If listening doesn't exist, this object is not currently
 209        // listening to obj. Break out early.
 210        if (!listening) break;
 211  
 212        listening.obj.off(name, callback, this);
 213        if (listening.interop) listening.off(name, callback);
 214      }
 215      if (_.isEmpty(listeningTo)) this._listeningTo = void 0;
 216  
 217      return this;
 218    };
 219  
 220    // The reducing API that removes a callback from the `events` object.
 221    var offApi = function(events, name, callback, options) {
 222      if (!events) return;
 223  
 224      var context = options.context, listeners = options.listeners;
 225      var i = 0, names;
 226  
 227      // Delete all event listeners and "drop" events.
 228      if (!name && !context && !callback) {
 229        for (names = _.keys(listeners); i < names.length; i++) {
 230          listeners[names[i]].cleanup();
 231        }
 232        return;
 233      }
 234  
 235      names = name ? [name] : _.keys(events);
 236      for (; i < names.length; i++) {
 237        name = names[i];
 238        var handlers = events[name];
 239  
 240        // Bail out if there are no events stored.
 241        if (!handlers) break;
 242  
 243        // Find any remaining events.
 244        var remaining = [];
 245        for (var j = 0; j < handlers.length; j++) {
 246          var handler = handlers[j];
 247          if (
 248            callback && callback !== handler.callback &&
 249              callback !== handler.callback._callback ||
 250                context && context !== handler.context
 251          ) {
 252            remaining.push(handler);
 253          } else {
 254            var listening = handler.listening;
 255            if (listening) listening.off(name, callback);
 256          }
 257        }
 258  
 259        // Replace events if there are any remaining.  Otherwise, clean up.
 260        if (remaining.length) {
 261          events[name] = remaining;
 262        } else {
 263          delete events[name];
 264        }
 265      }
 266  
 267      return events;
 268    };
 269  
 270    // Bind an event to only be triggered a single time. After the first time
 271    // the callback is invoked, its listener will be removed. If multiple events
 272    // are passed in using the space-separated syntax, the handler will fire
 273    // once for each event, not once for a combination of all events.
 274    Events.once = function(name, callback, context) {
 275      // Map the event into a `{event: once}` object.
 276      var events = eventsApi(onceMap, {}, name, callback, this.off.bind(this));
 277      if (typeof name === 'string' && context == null) callback = void 0;
 278      return this.on(events, callback, context);
 279    };
 280  
 281    // Inversion-of-control versions of `once`.
 282    Events.listenToOnce = function(obj, name, callback) {
 283      // Map the event into a `{event: once}` object.
 284      var events = eventsApi(onceMap, {}, name, callback, this.stopListening.bind(this, obj));
 285      return this.listenTo(obj, events);
 286    };
 287  
 288    // Reduces the event callbacks into a map of `{event: onceWrapper}`.
 289    // `offer` unbinds the `onceWrapper` after it has been called.
 290    var onceMap = function(map, name, callback, offer) {
 291      if (callback) {
 292        var once = map[name] = _.once(function() {
 293          offer(name, once);
 294          callback.apply(this, arguments);
 295        });
 296        once._callback = callback;
 297      }
 298      return map;
 299    };
 300  
 301    // Trigger one or many events, firing all bound callbacks. Callbacks are
 302    // passed the same arguments as `trigger` is, apart from the event name
 303    // (unless you're listening on `"all"`, which will cause your callback to
 304    // receive the true name of the event as the first argument).
 305    Events.trigger = function(name) {
 306      if (!this._events) return this;
 307  
 308      var length = Math.max(0, arguments.length - 1);
 309      var args = Array(length);
 310      for (var i = 0; i < length; i++) args[i] = arguments[i + 1];
 311  
 312      eventsApi(triggerApi, this._events, name, void 0, args);
 313      return this;
 314    };
 315  
 316    // Handles triggering the appropriate event callbacks.
 317    var triggerApi = function(objEvents, name, callback, args) {
 318      if (objEvents) {
 319        var events = objEvents[name];
 320        var allEvents = objEvents.all;
 321        if (events && allEvents) allEvents = allEvents.slice();
 322        if (events) triggerEvents(events, args);
 323        if (allEvents) triggerEvents(allEvents, [name].concat(args));
 324      }
 325      return objEvents;
 326    };
 327  
 328    // A difficult-to-believe, but optimized internal dispatch function for
 329    // triggering events. Tries to keep the usual cases speedy (most internal
 330    // Backbone events have 3 arguments).
 331    var triggerEvents = function(events, args) {
 332      var ev, i = -1, l = events.length, a1 = args[0], a2 = args[1], a3 = args[2];
 333      switch (args.length) {
 334        case 0: while (++i < l) (ev = events[i]).callback.call(ev.ctx); return;
 335        case 1: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1); return;
 336        case 2: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2); return;
 337        case 3: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2, a3); return;
 338        default: while (++i < l) (ev = events[i]).callback.apply(ev.ctx, args); return;
 339      }
 340    };
 341  
 342    // A listening class that tracks and cleans up memory bindings
 343    // when all callbacks have been offed.
 344    var Listening = function(listener, obj) {
 345      this.id = listener._listenId;
 346      this.listener = listener;
 347      this.obj = obj;
 348      this.interop = true;
 349      this.count = 0;
 350      this._events = void 0;
 351    };
 352  
 353    Listening.prototype.on = Events.on;
 354  
 355    // Offs a callback (or several).
 356    // Uses an optimized counter if the listenee uses Backbone.Events.
 357    // Otherwise, falls back to manual tracking to support events
 358    // library interop.
 359    Listening.prototype.off = function(name, callback) {
 360      var cleanup;
 361      if (this.interop) {
 362        this._events = eventsApi(offApi, this._events, name, callback, {
 363          context: void 0,
 364          listeners: void 0
 365        });
 366        cleanup = !this._events;
 367      } else {
 368        this.count--;
 369        cleanup = this.count === 0;
 370      }
 371      if (cleanup) this.cleanup();
 372    };
 373  
 374    // Cleans up memory bindings between the listener and the listenee.
 375    Listening.prototype.cleanup = function() {
 376      delete this.listener._listeningTo[this.obj._listenId];
 377      if (!this.interop) delete this.obj._listeners[this.id];
 378    };
 379  
 380    // Aliases for backwards compatibility.
 381    Events.bind   = Events.on;
 382    Events.unbind = Events.off;
 383  
 384    // Allow the `Backbone` object to serve as a global event bus, for folks who
 385    // want global "pubsub" in a convenient place.
 386    _.extend(Backbone, Events);
 387  
 388    // Backbone.Model
 389    // --------------
 390  
 391    // Backbone **Models** are the basic data object in the framework --
 392    // frequently representing a row in a table in a database on your server.
 393    // A discrete chunk of data and a bunch of useful, related methods for
 394    // performing computations and transformations on that data.
 395  
 396    // Create a new model with the specified attributes. A client id (`cid`)
 397    // is automatically generated and assigned for you.
 398    var Model = Backbone.Model = function(attributes, options) {
 399      var attrs = attributes || {};
 400      options || (options = {});
 401      this.preinitialize.apply(this, arguments);
 402      this.cid = _.uniqueId(this.cidPrefix);
 403      this.attributes = {};
 404      if (options.collection) this.collection = options.collection;
 405      if (options.parse) attrs = this.parse(attrs, options) || {};
 406      var defaults = _.result(this, 'defaults');
 407  
 408      // Just _.defaults would work fine, but the additional _.extends
 409      // is in there for historical reasons. See #3843.
 410      attrs = _.defaults(_.extend({}, defaults, attrs), defaults);
 411  
 412      this.set(attrs, options);
 413      this.changed = {};
 414      this.initialize.apply(this, arguments);
 415    };
 416  
 417    // Attach all inheritable methods to the Model prototype.
 418    _.extend(Model.prototype, Events, {
 419  
 420      // A hash of attributes whose current and previous value differ.
 421      changed: null,
 422  
 423      // The value returned during the last failed validation.
 424      validationError: null,
 425  
 426      // The default name for the JSON `id` attribute is `"id"`. MongoDB and
 427      // CouchDB users may want to set this to `"_id"`.
 428      idAttribute: 'id',
 429  
 430      // The prefix is used to create the client id which is used to identify models locally.
 431      // You may want to override this if you're experiencing name clashes with model ids.
 432      cidPrefix: 'c',
 433  
 434      // preinitialize is an empty function by default. You can override it with a function
 435      // or object.  preinitialize will run before any instantiation logic is run in the Model.
 436      preinitialize: function(){},
 437  
 438      // Initialize is an empty function by default. Override it with your own
 439      // initialization logic.
 440      initialize: function(){},
 441  
 442      // Return a copy of the model's `attributes` object.
 443      toJSON: function(options) {
 444        return _.clone(this.attributes);
 445      },
 446  
 447      // Proxy `Backbone.sync` by default -- but override this if you need
 448      // custom syncing semantics for *this* particular model.
 449      sync: function() {
 450        return Backbone.sync.apply(this, arguments);
 451      },
 452  
 453      // Get the value of an attribute.
 454      get: function(attr) {
 455        return this.attributes[attr];
 456      },
 457  
 458      // Get the HTML-escaped value of an attribute.
 459      escape: function(attr) {
 460        return _.escape(this.get(attr));
 461      },
 462  
 463      // Returns `true` if the attribute contains a value that is not null
 464      // or undefined.
 465      has: function(attr) {
 466        return this.get(attr) != null;
 467      },
 468  
 469      // Special-cased proxy to underscore's `_.matches` method.
 470      matches: function(attrs) {
 471        return !!_.iteratee(attrs, this)(this.attributes);
 472      },
 473  
 474      // Set a hash of model attributes on the object, firing `"change"`. This is
 475      // the core primitive operation of a model, updating the data and notifying
 476      // anyone who needs to know about the change in state. The heart of the beast.
 477      set: function(key, val, options) {
 478        if (key == null) return this;
 479  
 480        // Handle both `"key", value` and `{key: value}` -style arguments.
 481        var attrs;
 482        if (typeof key === 'object') {
 483          attrs = key;
 484          options = val;
 485        } else {
 486          (attrs = {})[key] = val;
 487        }
 488  
 489        options || (options = {});
 490  
 491        // Run validation.
 492        if (!this._validate(attrs, options)) return false;
 493  
 494        // Extract attributes and options.
 495        var unset      = options.unset;
 496        var silent     = options.silent;
 497        var changes    = [];
 498        var changing   = this._changing;
 499        this._changing = true;
 500  
 501        if (!changing) {
 502          this._previousAttributes = _.clone(this.attributes);
 503          this.changed = {};
 504        }
 505  
 506        var current = this.attributes;
 507        var changed = this.changed;
 508        var prev    = this._previousAttributes;
 509  
 510        // For each `set` attribute, update or delete the current value.
 511        for (var attr in attrs) {
 512          val = attrs[attr];
 513          if (!_.isEqual(current[attr], val)) changes.push(attr);
 514          if (!_.isEqual(prev[attr], val)) {
 515            changed[attr] = val;
 516          } else {
 517            delete changed[attr];
 518          }
 519          unset ? delete current[attr] : current[attr] = val;
 520        }
 521  
 522        // Update the `id`.
 523        if (this.idAttribute in attrs) {
 524          var prevId = this.id;
 525          this.id = this.get(this.idAttribute);
 526          this.trigger('changeId', this, prevId, options);
 527        }
 528  
 529        // Trigger all relevant attribute changes.
 530        if (!silent) {
 531          if (changes.length) this._pending = options;
 532          for (var i = 0; i < changes.length; i++) {
 533            this.trigger('change:' + changes[i], this, current[changes[i]], options);
 534          }
 535        }
 536  
 537        // You might be wondering why there's a `while` loop here. Changes can
 538        // be recursively nested within `"change"` events.
 539        if (changing) return this;
 540        if (!silent) {
 541          while (this._pending) {
 542            options = this._pending;
 543            this._pending = false;
 544            this.trigger('change', this, options);
 545          }
 546        }
 547        this._pending = false;
 548        this._changing = false;
 549        return this;
 550      },
 551  
 552      // Remove an attribute from the model, firing `"change"`. `unset` is a noop
 553      // if the attribute doesn't exist.
 554      unset: function(attr, options) {
 555        return this.set(attr, void 0, _.extend({}, options, {unset: true}));
 556      },
 557  
 558      // Clear all attributes on the model, firing `"change"`.
 559      clear: function(options) {
 560        var attrs = {};
 561        for (var key in this.attributes) attrs[key] = void 0;
 562        return this.set(attrs, _.extend({}, options, {unset: true}));
 563      },
 564  
 565      // Determine if the model has changed since the last `"change"` event.
 566      // If you specify an attribute name, determine if that attribute has changed.
 567      hasChanged: function(attr) {
 568        if (attr == null) return !_.isEmpty(this.changed);
 569        return _.has(this.changed, attr);
 570      },
 571  
 572      // Return an object containing all the attributes that have changed, or
 573      // false if there are no changed attributes. Useful for determining what
 574      // parts of a view need to be updated and/or what attributes need to be
 575      // persisted to the server. Unset attributes will be set to undefined.
 576      // You can also pass an attributes object to diff against the model,
 577      // determining if there *would be* a change.
 578      changedAttributes: function(diff) {
 579        if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
 580        var old = this._changing ? this._previousAttributes : this.attributes;
 581        var changed = {};
 582        var hasChanged;
 583        for (var attr in diff) {
 584          var val = diff[attr];
 585          if (_.isEqual(old[attr], val)) continue;
 586          changed[attr] = val;
 587          hasChanged = true;
 588        }
 589        return hasChanged ? changed : false;
 590      },
 591  
 592      // Get the previous value of an attribute, recorded at the time the last
 593      // `"change"` event was fired.
 594      previous: function(attr) {
 595        if (attr == null || !this._previousAttributes) return null;
 596        return this._previousAttributes[attr];
 597      },
 598  
 599      // Get all of the attributes of the model at the time of the previous
 600      // `"change"` event.
 601      previousAttributes: function() {
 602        return _.clone(this._previousAttributes);
 603      },
 604  
 605      // Fetch the model from the server, merging the response with the model's
 606      // local attributes. Any changed attributes will trigger a "change" event.
 607      fetch: function(options) {
 608        options = _.extend({parse: true}, options);
 609        var model = this;
 610        var success = options.success;
 611        options.success = function(resp) {
 612          var serverAttrs = options.parse ? model.parse(resp, options) : resp;
 613          if (!model.set(serverAttrs, options)) return false;
 614          if (success) success.call(options.context, model, resp, options);
 615          model.trigger('sync', model, resp, options);
 616        };
 617        wrapError(this, options);
 618        return this.sync('read', this, options);
 619      },
 620  
 621      // Set a hash of model attributes, and sync the model to the server.
 622      // If the server returns an attributes hash that differs, the model's
 623      // state will be `set` again.
 624      save: function(key, val, options) {
 625        // Handle both `"key", value` and `{key: value}` -style arguments.
 626        var attrs;
 627        if (key == null || typeof key === 'object') {
 628          attrs = key;
 629          options = val;
 630        } else {
 631          (attrs = {})[key] = val;
 632        }
 633  
 634        options = _.extend({validate: true, parse: true}, options);
 635        var wait = options.wait;
 636  
 637        // If we're not waiting and attributes exist, save acts as
 638        // `set(attr).save(null, opts)` with validation. Otherwise, check if
 639        // the model will be valid when the attributes, if any, are set.
 640        if (attrs && !wait) {
 641          if (!this.set(attrs, options)) return false;
 642        } else if (!this._validate(attrs, options)) {
 643          return false;
 644        }
 645  
 646        // After a successful server-side save, the client is (optionally)
 647        // updated with the server-side state.
 648        var model = this;
 649        var success = options.success;
 650        var attributes = this.attributes;
 651        options.success = function(resp) {
 652          // Ensure attributes are restored during synchronous saves.
 653          model.attributes = attributes;
 654          var serverAttrs = options.parse ? model.parse(resp, options) : resp;
 655          if (wait) serverAttrs = _.extend({}, attrs, serverAttrs);
 656          if (serverAttrs && !model.set(serverAttrs, options)) return false;
 657          if (success) success.call(options.context, model, resp, options);
 658          model.trigger('sync', model, resp, options);
 659        };
 660        wrapError(this, options);
 661  
 662        // Set temporary attributes if `{wait: true}` to properly find new ids.
 663        if (attrs && wait) this.attributes = _.extend({}, attributes, attrs);
 664  
 665        var method = this.isNew() ? 'create' : options.patch ? 'patch' : 'update';
 666        if (method === 'patch' && !options.attrs) options.attrs = attrs;
 667        var xhr = this.sync(method, this, options);
 668  
 669        // Restore attributes.
 670        this.attributes = attributes;
 671  
 672        return xhr;
 673      },
 674  
 675      // Destroy this model on the server if it was already persisted.
 676      // Optimistically removes the model from its collection, if it has one.
 677      // If `wait: true` is passed, waits for the server to respond before removal.
 678      destroy: function(options) {
 679        options = options ? _.clone(options) : {};
 680        var model = this;
 681        var success = options.success;
 682        var wait = options.wait;
 683  
 684        var destroy = function() {
 685          model.stopListening();
 686          model.trigger('destroy', model, model.collection, options);
 687        };
 688  
 689        options.success = function(resp) {
 690          if (wait) destroy();
 691          if (success) success.call(options.context, model, resp, options);
 692          if (!model.isNew()) model.trigger('sync', model, resp, options);
 693        };
 694  
 695        var xhr = false;
 696        if (this.isNew()) {
 697          _.defer(options.success);
 698        } else {
 699          wrapError(this, options);
 700          xhr = this.sync('delete', this, options);
 701        }
 702        if (!wait) destroy();
 703        return xhr;
 704      },
 705  
 706      // Default URL for the model's representation on the server -- if you're
 707      // using Backbone's restful methods, override this to change the endpoint
 708      // that will be called.
 709      url: function() {
 710        var base =
 711          _.result(this, 'urlRoot') ||
 712          _.result(this.collection, 'url') ||
 713          urlError();
 714        if (this.isNew()) return base;
 715        var id = this.get(this.idAttribute);
 716        return base.replace(/[^\/]$/, '$&/') + encodeURIComponent(id);
 717      },
 718  
 719      // **parse** converts a response into the hash of attributes to be `set` on
 720      // the model. The default implementation is just to pass the response along.
 721      parse: function(resp, options) {
 722        return resp;
 723      },
 724  
 725      // Create a new model with identical attributes to this one.
 726      clone: function() {
 727        return new this.constructor(this.attributes);
 728      },
 729  
 730      // A model is new if it has never been saved to the server, and lacks an id.
 731      isNew: function() {
 732        return !this.has(this.idAttribute);
 733      },
 734  
 735      // Check if the model is currently in a valid state.
 736      isValid: function(options) {
 737        return this._validate({}, _.extend({}, options, {validate: true}));
 738      },
 739  
 740      // Run validation against the next complete set of model attributes,
 741      // returning `true` if all is well. Otherwise, fire an `"invalid"` event.
 742      _validate: function(attrs, options) {
 743        if (!options.validate || !this.validate) return true;
 744        attrs = _.extend({}, this.attributes, attrs);
 745        var error = this.validationError = this.validate(attrs, options) || null;
 746        if (!error) return true;
 747        this.trigger('invalid', this, error, _.extend(options, {validationError: error}));
 748        return false;
 749      }
 750  
 751    });
 752  
 753    // Backbone.Collection
 754    // -------------------
 755  
 756    // If models tend to represent a single row of data, a Backbone Collection is
 757    // more analogous to a table full of data ... or a small slice or page of that
 758    // table, or a collection of rows that belong together for a particular reason
 759    // -- all of the messages in this particular folder, all of the documents
 760    // belonging to this particular author, and so on. Collections maintain
 761    // indexes of their models, both in order, and for lookup by `id`.
 762  
 763    // Create a new **Collection**, perhaps to contain a specific type of `model`.
 764    // If a `comparator` is specified, the Collection will maintain
 765    // its models in sort order, as they're added and removed.
 766    var Collection = Backbone.Collection = function(models, options) {
 767      options || (options = {});
 768      this.preinitialize.apply(this, arguments);
 769      if (options.model) this.model = options.model;
 770      if (options.comparator !== void 0) this.comparator = options.comparator;
 771      this._reset();
 772      this.initialize.apply(this, arguments);
 773      if (models) this.reset(models, _.extend({silent: true}, options));
 774    };
 775  
 776    // Default options for `Collection#set`.
 777    var setOptions = {add: true, remove: true, merge: true};
 778    var addOptions = {add: true, remove: false};
 779  
 780    // Splices `insert` into `array` at index `at`.
 781    var splice = function(array, insert, at) {
 782      at = Math.min(Math.max(at, 0), array.length);
 783      var tail = Array(array.length - at);
 784      var length = insert.length;
 785      var i;
 786      for (i = 0; i < tail.length; i++) tail[i] = array[i + at];
 787      for (i = 0; i < length; i++) array[i + at] = insert[i];
 788      for (i = 0; i < tail.length; i++) array[i + length + at] = tail[i];
 789    };
 790  
 791    // Define the Collection's inheritable methods.
 792    _.extend(Collection.prototype, Events, {
 793  
 794      // The default model for a collection is just a **Backbone.Model**.
 795      // This should be overridden in most cases.
 796      model: Model,
 797  
 798  
 799      // preinitialize is an empty function by default. You can override it with a function
 800      // or object.  preinitialize will run before any instantiation logic is run in the Collection.
 801      preinitialize: function(){},
 802  
 803      // Initialize is an empty function by default. Override it with your own
 804      // initialization logic.
 805      initialize: function(){},
 806  
 807      // The JSON representation of a Collection is an array of the
 808      // models' attributes.
 809      toJSON: function(options) {
 810        return this.map(function(model) { return model.toJSON(options); });
 811      },
 812  
 813      // Proxy `Backbone.sync` by default.
 814      sync: function() {
 815        return Backbone.sync.apply(this, arguments);
 816      },
 817  
 818      // Add a model, or list of models to the set. `models` may be Backbone
 819      // Models or raw JavaScript objects to be converted to Models, or any
 820      // combination of the two.
 821      add: function(models, options) {
 822        return this.set(models, _.extend({merge: false}, options, addOptions));
 823      },
 824  
 825      // Remove a model, or a list of models from the set.
 826      remove: function(models, options) {
 827        options = _.extend({}, options);
 828        var singular = !_.isArray(models);
 829        models = singular ? [models] : models.slice();
 830        var removed = this._removeModels(models, options);
 831        if (!options.silent && removed.length) {
 832          options.changes = {added: [], merged: [], removed: removed};
 833          this.trigger('update', this, options);
 834        }
 835        return singular ? removed[0] : removed;
 836      },
 837  
 838      // Update a collection by `set`-ing a new list of models, adding new ones,
 839      // removing models that are no longer present, and merging models that
 840      // already exist in the collection, as necessary. Similar to **Model#set**,
 841      // the core operation for updating the data contained by the collection.
 842      set: function(models, options) {
 843        if (models == null) return;
 844  
 845        options = _.extend({}, setOptions, options);
 846        if (options.parse && !this._isModel(models)) {
 847          models = this.parse(models, options) || [];
 848        }
 849  
 850        var singular = !_.isArray(models);
 851        models = singular ? [models] : models.slice();
 852  
 853        var at = options.at;
 854        if (at != null) at = +at;
 855        if (at > this.length) at = this.length;
 856        if (at < 0) at += this.length + 1;
 857  
 858        var set = [];
 859        var toAdd = [];
 860        var toMerge = [];
 861        var toRemove = [];
 862        var modelMap = {};
 863  
 864        var add = options.add;
 865        var merge = options.merge;
 866        var remove = options.remove;
 867  
 868        var sort = false;
 869        var sortable = this.comparator && at == null && options.sort !== false;
 870        var sortAttr = _.isString(this.comparator) ? this.comparator : null;
 871  
 872        // Turn bare objects into model references, and prevent invalid models
 873        // from being added.
 874        var model, i;
 875        for (i = 0; i < models.length; i++) {
 876          model = models[i];
 877  
 878          // If a duplicate is found, prevent it from being added and
 879          // optionally merge it into the existing model.
 880          var existing = this.get(model);
 881          if (existing) {
 882            if (merge && model !== existing) {
 883              var attrs = this._isModel(model) ? model.attributes : model;
 884              if (options.parse) attrs = existing.parse(attrs, options);
 885              existing.set(attrs, options);
 886              toMerge.push(existing);
 887              if (sortable && !sort) sort = existing.hasChanged(sortAttr);
 888            }
 889            if (!modelMap[existing.cid]) {
 890              modelMap[existing.cid] = true;
 891              set.push(existing);
 892            }
 893            models[i] = existing;
 894  
 895          // If this is a new, valid model, push it to the `toAdd` list.
 896          } else if (add) {
 897            model = models[i] = this._prepareModel(model, options);
 898            if (model) {
 899              toAdd.push(model);
 900              this._addReference(model, options);
 901              modelMap[model.cid] = true;
 902              set.push(model);
 903            }
 904          }
 905        }
 906  
 907        // Remove stale models.
 908        if (remove) {
 909          for (i = 0; i < this.length; i++) {
 910            model = this.models[i];
 911            if (!modelMap[model.cid]) toRemove.push(model);
 912          }
 913          if (toRemove.length) this._removeModels(toRemove, options);
 914        }
 915  
 916        // See if sorting is needed, update `length` and splice in new models.
 917        var orderChanged = false;
 918        var replace = !sortable && add && remove;
 919        if (set.length && replace) {
 920          orderChanged = this.length !== set.length || _.some(this.models, function(m, index) {
 921            return m !== set[index];
 922          });
 923          this.models.length = 0;
 924          splice(this.models, set, 0);
 925          this.length = this.models.length;
 926        } else if (toAdd.length) {
 927          if (sortable) sort = true;
 928          splice(this.models, toAdd, at == null ? this.length : at);
 929          this.length = this.models.length;
 930        }
 931  
 932        // Silently sort the collection if appropriate.
 933        if (sort) this.sort({silent: true});
 934  
 935        // Unless silenced, it's time to fire all appropriate add/sort/update events.
 936        if (!options.silent) {
 937          for (i = 0; i < toAdd.length; i++) {
 938            if (at != null) options.index = at + i;
 939            model = toAdd[i];
 940            model.trigger('add', model, this, options);
 941          }
 942          if (sort || orderChanged) this.trigger('sort', this, options);
 943          if (toAdd.length || toRemove.length || toMerge.length) {
 944            options.changes = {
 945              added: toAdd,
 946              removed: toRemove,
 947              merged: toMerge
 948            };
 949            this.trigger('update', this, options);
 950          }
 951        }
 952  
 953        // Return the added (or merged) model (or models).
 954        return singular ? models[0] : models;
 955      },
 956  
 957      // When you have more items than you want to add or remove individually,
 958      // you can reset the entire set with a new list of models, without firing
 959      // any granular `add` or `remove` events. Fires `reset` when finished.
 960      // Useful for bulk operations and optimizations.
 961      reset: function(models, options) {
 962        options = options ? _.clone(options) : {};
 963        for (var i = 0; i < this.models.length; i++) {
 964          this._removeReference(this.models[i], options);
 965        }
 966        options.previousModels = this.models;
 967        this._reset();
 968        models = this.add(models, _.extend({silent: true}, options));
 969        if (!options.silent) this.trigger('reset', this, options);
 970        return models;
 971      },
 972  
 973      // Add a model to the end of the collection.
 974      push: function(model, options) {
 975        return this.add(model, _.extend({at: this.length}, options));
 976      },
 977  
 978      // Remove a model from the end of the collection.
 979      pop: function(options) {
 980        var model = this.at(this.length - 1);
 981        return this.remove(model, options);
 982      },
 983  
 984      // Add a model to the beginning of the collection.
 985      unshift: function(model, options) {
 986        return this.add(model, _.extend({at: 0}, options));
 987      },
 988  
 989      // Remove a model from the beginning of the collection.
 990      shift: function(options) {
 991        var model = this.at(0);
 992        return this.remove(model, options);
 993      },
 994  
 995      // Slice out a sub-array of models from the collection.
 996      slice: function() {
 997        return slice.apply(this.models, arguments);
 998      },
 999  
1000      // Get a model from the set by id, cid, model object with id or cid
1001      // properties, or an attributes object that is transformed through modelId.
1002      get: function(obj) {
1003        if (obj == null) return void 0;
1004        return this._byId[obj] ||
1005          this._byId[this.modelId(this._isModel(obj) ? obj.attributes : obj, obj.idAttribute)] ||
1006          obj.cid && this._byId[obj.cid];
1007      },
1008  
1009      // Returns `true` if the model is in the collection.
1010      has: function(obj) {
1011        return this.get(obj) != null;
1012      },
1013  
1014      // Get the model at the given index.
1015      at: function(index) {
1016        if (index < 0) index += this.length;
1017        return this.models[index];
1018      },
1019  
1020      // Return models with matching attributes. Useful for simple cases of
1021      // `filter`.
1022      where: function(attrs, first) {
1023        return this[first ? 'find' : 'filter'](attrs);
1024      },
1025  
1026      // Return the first model with matching attributes. Useful for simple cases
1027      // of `find`.
1028      findWhere: function(attrs) {
1029        return this.where(attrs, true);
1030      },
1031  
1032      // Force the collection to re-sort itself. You don't need to call this under
1033      // normal circumstances, as the set will maintain sort order as each item
1034      // is added.
1035      sort: function(options) {
1036        var comparator = this.comparator;
1037        if (!comparator) throw new Error('Cannot sort a set without a comparator');
1038        options || (options = {});
1039  
1040        var length = comparator.length;
1041        if (_.isFunction(comparator)) comparator = comparator.bind(this);
1042  
1043        // Run sort based on type of `comparator`.
1044        if (length === 1 || _.isString(comparator)) {
1045          this.models = this.sortBy(comparator);
1046        } else {
1047          this.models.sort(comparator);
1048        }
1049        if (!options.silent) this.trigger('sort', this, options);
1050        return this;
1051      },
1052  
1053      // Pluck an attribute from each model in the collection.
1054      pluck: function(attr) {
1055        return this.map(attr + '');
1056      },
1057  
1058      // Fetch the default set of models for this collection, resetting the
1059      // collection when they arrive. If `reset: true` is passed, the response
1060      // data will be passed through the `reset` method instead of `set`.
1061      fetch: function(options) {
1062        options = _.extend({parse: true}, options);
1063        var success = options.success;
1064        var collection = this;
1065        options.success = function(resp) {
1066          var method = options.reset ? 'reset' : 'set';
1067          collection[method](resp, options);
1068          if (success) success.call(options.context, collection, resp, options);
1069          collection.trigger('sync', collection, resp, options);
1070        };
1071        wrapError(this, options);
1072        return this.sync('read', this, options);
1073      },
1074  
1075      // Create a new instance of a model in this collection. Add the model to the
1076      // collection immediately, unless `wait: true` is passed, in which case we
1077      // wait for the server to agree.
1078      create: function(model, options) {
1079        options = options ? _.clone(options) : {};
1080        var wait = options.wait;
1081        model = this._prepareModel(model, options);
1082        if (!model) return false;
1083        if (!wait) this.add(model, options);
1084        var collection = this;
1085        var success = options.success;
1086        options.success = function(m, resp, callbackOpts) {
1087          if (wait) {
1088            m.off('error', collection._forwardPristineError, collection);
1089            collection.add(m, callbackOpts);
1090          }
1091          if (success) success.call(callbackOpts.context, m, resp, callbackOpts);
1092        };
1093        // In case of wait:true, our collection is not listening to any
1094        // of the model's events yet, so it will not forward the error
1095        // event. In this special case, we need to listen for it
1096        // separately and handle the event just once.
1097        // (The reason we don't need to do this for the sync event is
1098        // in the success handler above: we add the model first, which
1099        // causes the collection to listen, and then invoke the callback
1100        // that triggers the event.)
1101        if (wait) {
1102          model.once('error', this._forwardPristineError, this);
1103        }
1104        model.save(null, options);
1105        return model;
1106      },
1107  
1108      // **parse** converts a response into a list of models to be added to the
1109      // collection. The default implementation is just to pass it through.
1110      parse: function(resp, options) {
1111        return resp;
1112      },
1113  
1114      // Create a new collection with an identical list of models as this one.
1115      clone: function() {
1116        return new this.constructor(this.models, {
1117          model: this.model,
1118          comparator: this.comparator
1119        });
1120      },
1121  
1122      // Define how to uniquely identify models in the collection.
1123      modelId: function(attrs, idAttribute) {
1124        return attrs[idAttribute || this.model.prototype.idAttribute || 'id'];
1125      },
1126  
1127      // Get an iterator of all models in this collection.
1128      values: function() {
1129        return new CollectionIterator(this, ITERATOR_VALUES);
1130      },
1131  
1132      // Get an iterator of all model IDs in this collection.
1133      keys: function() {
1134        return new CollectionIterator(this, ITERATOR_KEYS);
1135      },
1136  
1137      // Get an iterator of all [ID, model] tuples in this collection.
1138      entries: function() {
1139        return new CollectionIterator(this, ITERATOR_KEYSVALUES);
1140      },
1141  
1142      // Private method to reset all internal state. Called when the collection
1143      // is first initialized or reset.
1144      _reset: function() {
1145        this.length = 0;
1146        this.models = [];
1147        this._byId  = {};
1148      },
1149  
1150      // Prepare a hash of attributes (or other model) to be added to this
1151      // collection.
1152      _prepareModel: function(attrs, options) {
1153        if (this._isModel(attrs)) {
1154          if (!attrs.collection) attrs.collection = this;
1155          return attrs;
1156        }
1157        options = options ? _.clone(options) : {};
1158        options.collection = this;
1159  
1160        var model;
1161        if (this.model.prototype) {
1162          model = new this.model(attrs, options);
1163        } else {
1164          // ES class methods didn't have prototype
1165          model = this.model(attrs, options);
1166        }
1167  
1168        if (!model.validationError) return model;
1169        this.trigger('invalid', this, model.validationError, options);
1170        return false;
1171      },
1172  
1173      // Internal method called by both remove and set.
1174      _removeModels: function(models, options) {
1175        var removed = [];
1176        for (var i = 0; i < models.length; i++) {
1177          var model = this.get(models[i]);
1178          if (!model) continue;
1179  
1180          var index = this.indexOf(model);
1181          this.models.splice(index, 1);
1182          this.length--;
1183  
1184          // Remove references before triggering 'remove' event to prevent an
1185          // infinite loop. #3693
1186          delete this._byId[model.cid];
1187          var id = this.modelId(model.attributes, model.idAttribute);
1188          if (id != null) delete this._byId[id];
1189  
1190          if (!options.silent) {
1191            options.index = index;
1192            model.trigger('remove', model, this, options);
1193          }
1194  
1195          removed.push(model);
1196          this._removeReference(model, options);
1197        }
1198        if (models.length > 0 && !options.silent) delete options.index;
1199        return removed;
1200      },
1201  
1202      // Method for checking whether an object should be considered a model for
1203      // the purposes of adding to the collection.
1204      _isModel: function(model) {
1205        return model instanceof Model;
1206      },
1207  
1208      // Internal method to create a model's ties to a collection.
1209      _addReference: function(model, options) {
1210        this._byId[model.cid] = model;
1211        var id = this.modelId(model.attributes, model.idAttribute);
1212        if (id != null) this._byId[id] = model;
1213        model.on('all', this._onModelEvent, this);
1214      },
1215  
1216      // Internal method to sever a model's ties to a collection.
1217      _removeReference: function(model, options) {
1218        delete this._byId[model.cid];
1219        var id = this.modelId(model.attributes, model.idAttribute);
1220        if (id != null) delete this._byId[id];
1221        if (this === model.collection) delete model.collection;
1222        model.off('all', this._onModelEvent, this);
1223      },
1224  
1225      // Internal method called every time a model in the set fires an event.
1226      // Sets need to update their indexes when models change ids. All other
1227      // events simply proxy through. "add" and "remove" events that originate
1228      // in other collections are ignored.
1229      _onModelEvent: function(event, model, collection, options) {
1230        if (model) {
1231          if ((event === 'add' || event === 'remove') && collection !== this) return;
1232          if (event === 'destroy') this.remove(model, options);
1233          if (event === 'changeId') {
1234            var prevId = this.modelId(model.previousAttributes(), model.idAttribute);
1235            var id = this.modelId(model.attributes, model.idAttribute);
1236            if (prevId != null) delete this._byId[prevId];
1237            if (id != null) this._byId[id] = model;
1238          }
1239        }
1240        this.trigger.apply(this, arguments);
1241      },
1242  
1243      // Internal callback method used in `create`. It serves as a
1244      // stand-in for the `_onModelEvent` method, which is not yet bound
1245      // during the `wait` period of the `create` call. We still want to
1246      // forward any `'error'` event at the end of the `wait` period,
1247      // hence a customized callback.
1248      _forwardPristineError: function(model, collection, options) {
1249        // Prevent double forward if the model was already in the
1250        // collection before the call to `create`.
1251        if (this.has(model)) return;
1252        this._onModelEvent('error', model, collection, options);
1253      }
1254    });
1255  
1256    // Defining an @@iterator method implements JavaScript's Iterable protocol.
1257    // In modern ES2015 browsers, this value is found at Symbol.iterator.
1258    /* global Symbol */
1259    var $$iterator = typeof Symbol === 'function' && Symbol.iterator;
1260    if ($$iterator) {
1261      Collection.prototype[$$iterator] = Collection.prototype.values;
1262    }
1263  
1264    // CollectionIterator
1265    // ------------------
1266  
1267    // A CollectionIterator implements JavaScript's Iterator protocol, allowing the
1268    // use of `for of` loops in modern browsers and interoperation between
1269    // Backbone.Collection and other JavaScript functions and third-party libraries
1270    // which can operate on Iterables.
1271    var CollectionIterator = function(collection, kind) {
1272      this._collection = collection;
1273      this._kind = kind;
1274      this._index = 0;
1275    };
1276  
1277    // This "enum" defines the three possible kinds of values which can be emitted
1278    // by a CollectionIterator that correspond to the values(), keys() and entries()
1279    // methods on Collection, respectively.
1280    var ITERATOR_VALUES = 1;
1281    var ITERATOR_KEYS = 2;
1282    var ITERATOR_KEYSVALUES = 3;
1283  
1284    // All Iterators should themselves be Iterable.
1285    if ($$iterator) {
1286      CollectionIterator.prototype[$$iterator] = function() {
1287        return this;
1288      };
1289    }
1290  
1291    CollectionIterator.prototype.next = function() {
1292      if (this._collection) {
1293  
1294        // Only continue iterating if the iterated collection is long enough.
1295        if (this._index < this._collection.length) {
1296          var model = this._collection.at(this._index);
1297          this._index++;
1298  
1299          // Construct a value depending on what kind of values should be iterated.
1300          var value;
1301          if (this._kind === ITERATOR_VALUES) {
1302            value = model;
1303          } else {
1304            var id = this._collection.modelId(model.attributes, model.idAttribute);
1305            if (this._kind === ITERATOR_KEYS) {
1306              value = id;
1307            } else { // ITERATOR_KEYSVALUES
1308              value = [id, model];
1309            }
1310          }
1311          return {value: value, done: false};
1312        }
1313  
1314        // Once exhausted, remove the reference to the collection so future
1315        // calls to the next method always return done.
1316        this._collection = void 0;
1317      }
1318  
1319      return {value: void 0, done: true};
1320    };
1321  
1322    // Backbone.View
1323    // -------------
1324  
1325    // Backbone Views are almost more convention than they are actual code. A View
1326    // is simply a JavaScript object that represents a logical chunk of UI in the
1327    // DOM. This might be a single item, an entire list, a sidebar or panel, or
1328    // even the surrounding frame which wraps your whole app. Defining a chunk of
1329    // UI as a **View** allows you to define your DOM events declaratively, without
1330    // having to worry about render order ... and makes it easy for the view to
1331    // react to specific changes in the state of your models.
1332  
1333    // Creating a Backbone.View creates its initial element outside of the DOM,
1334    // if an existing element is not provided...
1335    var View = Backbone.View = function(options) {
1336      this.cid = _.uniqueId('view');
1337      this.preinitialize.apply(this, arguments);
1338      _.extend(this, _.pick(options, viewOptions));
1339      this._ensureElement();
1340      this.initialize.apply(this, arguments);
1341    };
1342  
1343    // Cached regex to split keys for `delegate`.
1344    var delegateEventSplitter = /^(\S+)\s*(.*)$/;
1345  
1346    // List of view options to be set as properties.
1347    var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName', 'events'];
1348  
1349    // Set up all inheritable **Backbone.View** properties and methods.
1350    _.extend(View.prototype, Events, {
1351  
1352      // The default `tagName` of a View's element is `"div"`.
1353      tagName: 'div',
1354  
1355      // jQuery delegate for element lookup, scoped to DOM elements within the
1356      // current view. This should be preferred to global lookups where possible.
1357      $: function(selector) {
1358        return this.$el.find(selector);
1359      },
1360  
1361      // preinitialize is an empty function by default. You can override it with a function
1362      // or object.  preinitialize will run before any instantiation logic is run in the View
1363      preinitialize: function(){},
1364  
1365      // Initialize is an empty function by default. Override it with your own
1366      // initialization logic.
1367      initialize: function(){},
1368  
1369      // **render** is the core function that your view should override, in order
1370      // to populate its element (`this.el`), with the appropriate HTML. The
1371      // convention is for **render** to always return `this`.
1372      render: function() {
1373        return this;
1374      },
1375  
1376      // Remove this view by taking the element out of the DOM, and removing any
1377      // applicable Backbone.Events listeners.
1378      remove: function() {
1379        this._removeElement();
1380        this.stopListening();
1381        return this;
1382      },
1383  
1384      // Remove this view's element from the document and all event listeners
1385      // attached to it. Exposed for subclasses using an alternative DOM
1386      // manipulation API.
1387      _removeElement: function() {
1388        this.$el.remove();
1389      },
1390  
1391      // Change the view's element (`this.el` property) and re-delegate the
1392      // view's events on the new element.
1393      setElement: function(element) {
1394        this.undelegateEvents();
1395        this._setElement(element);
1396        this.delegateEvents();
1397        return this;
1398      },
1399  
1400      // Creates the `this.el` and `this.$el` references for this view using the
1401      // given `el`. `el` can be a CSS selector or an HTML string, a jQuery
1402      // context or an element. Subclasses can override this to utilize an
1403      // alternative DOM manipulation API and are only required to set the
1404      // `this.el` property.
1405      _setElement: function(el) {
1406        this.$el = el instanceof Backbone.$ ? el : Backbone.$(el);
1407        this.el = this.$el[0];
1408      },
1409  
1410      // Set callbacks, where `this.events` is a hash of
1411      //
1412      // *{"event selector": "callback"}*
1413      //
1414      //     {
1415      //       'mousedown .title':  'edit',
1416      //       'click .button':     'save',
1417      //       'click .open':       function(e) { ... }
1418      //     }
1419      //
1420      // pairs. Callbacks will be bound to the view, with `this` set properly.
1421      // Uses event delegation for efficiency.
1422      // Omitting the selector binds the event to `this.el`.
1423      delegateEvents: function(events) {
1424        events || (events = _.result(this, 'events'));
1425        if (!events) return this;
1426        this.undelegateEvents();
1427        for (var key in events) {
1428          var method = events[key];
1429          if (!_.isFunction(method)) method = this[method];
1430          if (!method) continue;
1431          var match = key.match(delegateEventSplitter);
1432          this.delegate(match[1], match[2], method.bind(this));
1433        }
1434        return this;
1435      },
1436  
1437      // Add a single event listener to the view's element (or a child element
1438      // using `selector`). This only works for delegate-able events: not `focus`,
1439      // `blur`, and not `change`, `submit`, and `reset` in Internet Explorer.
1440      delegate: function(eventName, selector, listener) {
1441        this.$el.on(eventName + '.delegateEvents' + this.cid, selector, listener);
1442        return this;
1443      },
1444  
1445      // Clears all callbacks previously bound to the view by `delegateEvents`.
1446      // You usually don't need to use this, but may wish to if you have multiple
1447      // Backbone views attached to the same DOM element.
1448      undelegateEvents: function() {
1449        if (this.$el) this.$el.off('.delegateEvents' + this.cid);
1450        return this;
1451      },
1452  
1453      // A finer-grained `undelegateEvents` for removing a single delegated event.
1454      // `selector` and `listener` are both optional.
1455      undelegate: function(eventName, selector, listener) {
1456        this.$el.off(eventName + '.delegateEvents' + this.cid, selector, listener);
1457        return this;
1458      },
1459  
1460      // Produces a DOM element to be assigned to your view. Exposed for
1461      // subclasses using an alternative DOM manipulation API.
1462      _createElement: function(tagName) {
1463        return document.createElement(tagName);
1464      },
1465  
1466      // Ensure that the View has a DOM element to render into.
1467      // If `this.el` is a string, pass it through `$()`, take the first
1468      // matching element, and re-assign it to `el`. Otherwise, create
1469      // an element from the `id`, `className` and `tagName` properties.
1470      _ensureElement: function() {
1471        if (!this.el) {
1472          var attrs = _.extend({}, _.result(this, 'attributes'));
1473          if (this.id) attrs.id = _.result(this, 'id');
1474          if (this.className) attrs['class'] = _.result(this, 'className');
1475          this.setElement(this._createElement(_.result(this, 'tagName')));
1476          this._setAttributes(attrs);
1477        } else {
1478          this.setElement(_.result(this, 'el'));
1479        }
1480      },
1481  
1482      // Set attributes from a hash on this view's element.  Exposed for
1483      // subclasses using an alternative DOM manipulation API.
1484      _setAttributes: function(attributes) {
1485        this.$el.attr(attributes);
1486      }
1487  
1488    });
1489  
1490    // Proxy Backbone class methods to Underscore functions, wrapping the model's
1491    // `attributes` object or collection's `models` array behind the scenes.
1492    //
1493    // collection.filter(function(model) { return model.get('age') > 10 });
1494    // collection.each(this.addView);
1495    //
1496    // `Function#apply` can be slow so we use the method's arg count, if we know it.
1497    var addMethod = function(base, length, method, attribute) {
1498      switch (length) {
1499        case 1: return function() {
1500          return base[method](this[attribute]);
1501        };
1502        case 2: return function(value) {
1503          return base[method](this[attribute], value);
1504        };
1505        case 3: return function(iteratee, context) {
1506          return base[method](this[attribute], cb(iteratee, this), context);
1507        };
1508        case 4: return function(iteratee, defaultVal, context) {
1509          return base[method](this[attribute], cb(iteratee, this), defaultVal, context);
1510        };
1511        default: return function() {
1512          var args = slice.call(arguments);
1513          args.unshift(this[attribute]);
1514          return base[method].apply(base, args);
1515        };
1516      }
1517    };
1518  
1519    var addUnderscoreMethods = function(Class, base, methods, attribute) {
1520      _.each(methods, function(length, method) {
1521        if (base[method]) Class.prototype[method] = addMethod(base, length, method, attribute);
1522      });
1523    };
1524  
1525    // Support `collection.sortBy('attr')` and `collection.findWhere({id: 1})`.
1526    var cb = function(iteratee, instance) {
1527      if (_.isFunction(iteratee)) return iteratee;
1528      if (_.isObject(iteratee) && !instance._isModel(iteratee)) return modelMatcher(iteratee);
1529      if (_.isString(iteratee)) return function(model) { return model.get(iteratee); };
1530      return iteratee;
1531    };
1532    var modelMatcher = function(attrs) {
1533      var matcher = _.matches(attrs);
1534      return function(model) {
1535        return matcher(model.attributes);
1536      };
1537    };
1538  
1539    // Underscore methods that we want to implement on the Collection.
1540    // 90% of the core usefulness of Backbone Collections is actually implemented
1541    // right here:
1542    var collectionMethods = {forEach: 3, each: 3, map: 3, collect: 3, reduce: 0,
1543      foldl: 0, inject: 0, reduceRight: 0, foldr: 0, find: 3, detect: 3, filter: 3,
1544      select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 3, includes: 3,
1545      contains: 3, invoke: 0, max: 3, min: 3, toArray: 1, size: 1, first: 3,
1546      head: 3, take: 3, initial: 3, rest: 3, tail: 3, drop: 3, last: 3,
1547      without: 0, difference: 0, indexOf: 3, shuffle: 1, lastIndexOf: 3,
1548      isEmpty: 1, chain: 1, sample: 3, partition: 3, groupBy: 3, countBy: 3,
1549      sortBy: 3, indexBy: 3, findIndex: 3, findLastIndex: 3};
1550  
1551  
1552    // Underscore methods that we want to implement on the Model, mapped to the
1553    // number of arguments they take.
1554    var modelMethods = {keys: 1, values: 1, pairs: 1, invert: 1, pick: 0,
1555      omit: 0, chain: 1, isEmpty: 1};
1556  
1557    // Mix in each Underscore method as a proxy to `Collection#models`.
1558  
1559    _.each([
1560      [Collection, collectionMethods, 'models'],
1561      [Model, modelMethods, 'attributes']
1562    ], function(config) {
1563      var Base = config[0],
1564          methods = config[1],
1565          attribute = config[2];
1566  
1567      Base.mixin = function(obj) {
1568        var mappings = _.reduce(_.functions(obj), function(memo, name) {
1569          memo[name] = 0;
1570          return memo;
1571        }, {});
1572        addUnderscoreMethods(Base, obj, mappings, attribute);
1573      };
1574  
1575      addUnderscoreMethods(Base, _, methods, attribute);
1576    });
1577  
1578    // Backbone.sync
1579    // -------------
1580  
1581    // Override this function to change the manner in which Backbone persists
1582    // models to the server. You will be passed the type of request, and the
1583    // model in question. By default, makes a RESTful Ajax request
1584    // to the model's `url()`. Some possible customizations could be:
1585    //
1586    // * Use `setTimeout` to batch rapid-fire updates into a single request.
1587    // * Send up the models as XML instead of JSON.
1588    // * Persist models via WebSockets instead of Ajax.
1589    //
1590    // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
1591    // as `POST`, with a `_method` parameter containing the true HTTP method,
1592    // as well as all requests with the body as `application/x-www-form-urlencoded`
1593    // instead of `application/json` with the model in a param named `model`.
1594    // Useful when interfacing with server-side languages like **PHP** that make
1595    // it difficult to read the body of `PUT` requests.
1596    Backbone.sync = function(method, model, options) {
1597      var type = methodMap[method];
1598  
1599      // Default options, unless specified.
1600      _.defaults(options || (options = {}), {
1601        emulateHTTP: Backbone.emulateHTTP,
1602        emulateJSON: Backbone.emulateJSON
1603      });
1604  
1605      // Default JSON-request options.
1606      var params = {type: type, dataType: 'json'};
1607  
1608      // Ensure that we have a URL.
1609      if (!options.url) {
1610        params.url = _.result(model, 'url') || urlError();
1611      }
1612  
1613      // Ensure that we have the appropriate request data.
1614      if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
1615        params.contentType = 'application/json';
1616        params.data = JSON.stringify(options.attrs || model.toJSON(options));
1617      }
1618  
1619      // For older servers, emulate JSON by encoding the request into an HTML-form.
1620      if (options.emulateJSON) {
1621        params.contentType = 'application/x-www-form-urlencoded';
1622        params.data = params.data ? {model: params.data} : {};
1623      }
1624  
1625      // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
1626      // And an `X-HTTP-Method-Override` header.
1627      if (options.emulateHTTP && (type === 'PUT' || type === 'DELETE' || type === 'PATCH')) {
1628        params.type = 'POST';
1629        if (options.emulateJSON) params.data._method = type;
1630        var beforeSend = options.beforeSend;
1631        options.beforeSend = function(xhr) {
1632          xhr.setRequestHeader('X-HTTP-Method-Override', type);
1633          if (beforeSend) return beforeSend.apply(this, arguments);
1634        };
1635      }
1636  
1637      // Don't process data on a non-GET request.
1638      if (params.type !== 'GET' && !options.emulateJSON) {
1639        params.processData = false;
1640      }
1641  
1642      // Pass along `textStatus` and `errorThrown` from jQuery.
1643      var error = options.error;
1644      options.error = function(xhr, textStatus, errorThrown) {
1645        options.textStatus = textStatus;
1646        options.errorThrown = errorThrown;
1647        if (error) error.call(options.context, xhr, textStatus, errorThrown);
1648      };
1649  
1650      // Make the request, allowing the user to override any Ajax options.
1651      var xhr = options.xhr = Backbone.ajax(_.extend(params, options));
1652      model.trigger('request', model, xhr, options);
1653      return xhr;
1654    };
1655  
1656    // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
1657    var methodMap = {
1658      'create': 'POST',
1659      'update': 'PUT',
1660      'patch': 'PATCH',
1661      'delete': 'DELETE',
1662      'read': 'GET'
1663    };
1664  
1665    // Set the default implementation of `Backbone.ajax` to proxy through to `$`.
1666    // Override this if you'd like to use a different library.
1667    Backbone.ajax = function() {
1668      return Backbone.$.ajax.apply(Backbone.$, arguments);
1669    };
1670  
1671    // Backbone.Router
1672    // ---------------
1673  
1674    // Routers map faux-URLs to actions, and fire events when routes are
1675    // matched. Creating a new one sets its `routes` hash, if not set statically.
1676    var Router = Backbone.Router = function(options) {
1677      options || (options = {});
1678      this.preinitialize.apply(this, arguments);
1679      if (options.routes) this.routes = options.routes;
1680      this._bindRoutes();
1681      this.initialize.apply(this, arguments);
1682    };
1683  
1684    // Cached regular expressions for matching named param parts and splatted
1685    // parts of route strings.
1686    var optionalParam = /\((.*?)\)/g;
1687    var namedParam    = /(\(\?)?:\w+/g;
1688    var splatParam    = /\*\w+/g;
1689    var escapeRegExp  = /[\-{}\[\]+?.,\\\^$|#\s]/g;
1690  
1691    // Set up all inheritable **Backbone.Router** properties and methods.
1692    _.extend(Router.prototype, Events, {
1693  
1694      // preinitialize is an empty function by default. You can override it with a function
1695      // or object.  preinitialize will run before any instantiation logic is run in the Router.
1696      preinitialize: function(){},
1697  
1698      // Initialize is an empty function by default. Override it with your own
1699      // initialization logic.
1700      initialize: function(){},
1701  
1702      // Manually bind a single named route to a callback. For example:
1703      //
1704      //     this.route('search/:query/p:num', 'search', function(query, num) {
1705      //       ...
1706      //     });
1707      //
1708      route: function(route, name, callback) {
1709        if (!_.isRegExp(route)) route = this._routeToRegExp(route);
1710        if (_.isFunction(name)) {
1711          callback = name;
1712          name = '';
1713        }
1714        if (!callback) callback = this[name];
1715        var router = this;
1716        Backbone.history.route(route, function(fragment) {
1717          var args = router._extractParameters(route, fragment);
1718          if (router.execute(callback, args, name) !== false) {
1719            router.trigger.apply(router, ['route:' + name].concat(args));
1720            router.trigger('route', name, args);
1721            Backbone.history.trigger('route', router, name, args);
1722          }
1723        });
1724        return this;
1725      },
1726  
1727      // Execute a route handler with the provided parameters.  This is an
1728      // excellent place to do pre-route setup or post-route cleanup.
1729      execute: function(callback, args, name) {
1730        if (callback) callback.apply(this, args);
1731      },
1732  
1733      // Simple proxy to `Backbone.history` to save a fragment into the history.
1734      navigate: function(fragment, options) {
1735        Backbone.history.navigate(fragment, options);
1736        return this;
1737      },
1738  
1739      // Bind all defined routes to `Backbone.history`. We have to reverse the
1740      // order of the routes here to support behavior where the most general
1741      // routes can be defined at the bottom of the route map.
1742      _bindRoutes: function() {
1743        if (!this.routes) return;
1744        this.routes = _.result(this, 'routes');
1745        var route, routes = _.keys(this.routes);
1746        while ((route = routes.pop()) != null) {
1747          this.route(route, this.routes[route]);
1748        }
1749      },
1750  
1751      // Convert a route string into a regular expression, suitable for matching
1752      // against the current location hash.
1753      _routeToRegExp: function(route) {
1754        route = route.replace(escapeRegExp, '\\$&')
1755        .replace(optionalParam, '(?:$1)?')
1756        .replace(namedParam, function(match, optional) {
1757          return optional ? match : '([^/?]+)';
1758        })
1759        .replace(splatParam, '([^?]*?)');
1760        return new RegExp('^' + route + '(?:\\?([\\s\\S]*))?$');
1761      },
1762  
1763      // Given a route, and a URL fragment that it matches, return the array of
1764      // extracted decoded parameters. Empty or unmatched parameters will be
1765      // treated as `null` to normalize cross-browser behavior.
1766      _extractParameters: function(route, fragment) {
1767        var params = route.exec(fragment).slice(1);
1768        return _.map(params, function(param, i) {
1769          // Don't decode the search params.
1770          if (i === params.length - 1) return param || null;
1771          return param ? decodeURIComponent(param) : null;
1772        });
1773      }
1774  
1775    });
1776  
1777    // Backbone.History
1778    // ----------------
1779  
1780    // Handles cross-browser history management, based on either
1781    // [pushState](http://diveintohtml5.info/history.html) and real URLs, or
1782    // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)
1783    // and URL fragments. If the browser supports neither (old IE, natch),
1784    // falls back to polling.
1785    var History = Backbone.History = function() {
1786      this.handlers = [];
1787      this.checkUrl = this.checkUrl.bind(this);
1788  
1789      // Ensure that `History` can be used outside of the browser.
1790      if (typeof window !== 'undefined') {
1791        this.location = window.location;
1792        this.history = window.history;
1793      }
1794    };
1795  
1796    // Cached regex for stripping a leading hash/slash and trailing space.
1797    var routeStripper = /^[#\/]|\s+$/g;
1798  
1799    // Cached regex for stripping leading and trailing slashes.
1800    var rootStripper = /^\/+|\/+$/g;
1801  
1802    // Cached regex for stripping urls of hash.
1803    var pathStripper = /#.*$/;
1804  
1805    // Has the history handling already been started?
1806    History.started = false;
1807  
1808    // Set up all inheritable **Backbone.History** properties and methods.
1809    _.extend(History.prototype, Events, {
1810  
1811      // The default interval to poll for hash changes, if necessary, is
1812      // twenty times a second.
1813      interval: 50,
1814  
1815      // Are we at the app root?
1816      atRoot: function() {
1817        var path = this.location.pathname.replace(/[^\/]$/, '$&/');
1818        return path === this.root && !this.getSearch();
1819      },
1820  
1821      // Does the pathname match the root?
1822      matchRoot: function() {
1823        var path = this.decodeFragment(this.location.pathname);
1824        var rootPath = path.slice(0, this.root.length - 1) + '/';
1825        return rootPath === this.root;
1826      },
1827  
1828      // Unicode characters in `location.pathname` are percent encoded so they're
1829      // decoded for comparison. `%25` should not be decoded since it may be part
1830      // of an encoded parameter.
1831      decodeFragment: function(fragment) {
1832        return decodeURI(fragment.replace(/%25/g, '%2525'));
1833      },
1834  
1835      // In IE6, the hash fragment and search params are incorrect if the
1836      // fragment contains `?`.
1837      getSearch: function() {
1838        var match = this.location.href.replace(/#.*/, '').match(/\?.+/);
1839        return match ? match[0] : '';
1840      },
1841  
1842      // Gets the true hash value. Cannot use location.hash directly due to bug
1843      // in Firefox where location.hash will always be decoded.
1844      getHash: function(window) {
1845        var match = (window || this).location.href.match(/#(.*)$/);
1846        return match ? match[1] : '';
1847      },
1848  
1849      // Get the pathname and search params, without the root.
1850      getPath: function() {
1851        var path = this.decodeFragment(
1852          this.location.pathname + this.getSearch()
1853        ).slice(this.root.length - 1);
1854        return path.charAt(0) === '/' ? path.slice(1) : path;
1855      },
1856  
1857      // Get the cross-browser normalized URL fragment from the path or hash.
1858      getFragment: function(fragment) {
1859        if (fragment == null) {
1860          if (this._usePushState || !this._wantsHashChange) {
1861            fragment = this.getPath();
1862          } else {
1863            fragment = this.getHash();
1864          }
1865        }
1866        return fragment.replace(routeStripper, '');
1867      },
1868  
1869      // Start the hash change handling, returning `true` if the current URL matches
1870      // an existing route, and `false` otherwise.
1871      start: function(options) {
1872        if (History.started) throw new Error('Backbone.history has already been started');
1873        History.started = true;
1874  
1875        // Figure out the initial configuration. Do we need an iframe?
1876        // Is pushState desired ... is it available?
1877        this.options          = _.extend({root: '/'}, this.options, options);
1878        this.root             = this.options.root;
1879        this._trailingSlash   = this.options.trailingSlash;
1880        this._wantsHashChange = this.options.hashChange !== false;
1881        this._hasHashChange   = 'onhashchange' in window && (document.documentMode === void 0 || document.documentMode > 7);
1882        this._useHashChange   = this._wantsHashChange && this._hasHashChange;
1883        this._wantsPushState  = !!this.options.pushState;
1884        this._hasPushState    = !!(this.history && this.history.pushState);
1885        this._usePushState    = this._wantsPushState && this._hasPushState;
1886        this.fragment         = this.getFragment();
1887  
1888        // Normalize root to always include a leading and trailing slash.
1889        this.root = ('/' + this.root + '/').replace(rootStripper, '/');
1890  
1891        // Transition from hashChange to pushState or vice versa if both are
1892        // requested.
1893        if (this._wantsHashChange && this._wantsPushState) {
1894  
1895          // If we've started off with a route from a `pushState`-enabled
1896          // browser, but we're currently in a browser that doesn't support it...
1897          if (!this._hasPushState && !this.atRoot()) {
1898            var rootPath = this.root.slice(0, -1) || '/';
1899            this.location.replace(rootPath + '#' + this.getPath());
1900            // Return immediately as browser will do redirect to new url
1901            return true;
1902  
1903          // Or if we've started out with a hash-based route, but we're currently
1904          // in a browser where it could be `pushState`-based instead...
1905          } else if (this._hasPushState && this.atRoot()) {
1906            this.navigate(this.getHash(), {replace: true});
1907          }
1908  
1909        }
1910  
1911        // Proxy an iframe to handle location events if the browser doesn't
1912        // support the `hashchange` event, HTML5 history, or the user wants
1913        // `hashChange` but not `pushState`.
1914        if (!this._hasHashChange && this._wantsHashChange && !this._usePushState) {
1915          this.iframe = document.createElement('iframe');
1916          this.iframe.src = 'javascript:0';
1917          this.iframe.style.display = 'none';
1918          this.iframe.tabIndex = -1;
1919          var body = document.body;
1920          // Using `appendChild` will throw on IE < 9 if the document is not ready.
1921          var iWindow = body.insertBefore(this.iframe, body.firstChild).contentWindow;
1922          iWindow.document.open();
1923          iWindow.document.close();
1924          iWindow.location.hash = '#' + this.fragment;
1925        }
1926  
1927        // Add a cross-platform `addEventListener` shim for older browsers.
1928        var addEventListener = window.addEventListener || function(eventName, listener) {
1929          return attachEvent('on' + eventName, listener);
1930        };
1931  
1932        // Depending on whether we're using pushState or hashes, and whether
1933        // 'onhashchange' is supported, determine how we check the URL state.
1934        if (this._usePushState) {
1935          addEventListener('popstate', this.checkUrl, false);
1936        } else if (this._useHashChange && !this.iframe) {
1937          addEventListener('hashchange', this.checkUrl, false);
1938        } else if (this._wantsHashChange) {
1939          this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
1940        }
1941  
1942        if (!this.options.silent) return this.loadUrl();
1943      },
1944  
1945      // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
1946      // but possibly useful for unit testing Routers.
1947      stop: function() {
1948        // Add a cross-platform `removeEventListener` shim for older browsers.
1949        var removeEventListener = window.removeEventListener || function(eventName, listener) {
1950          return detachEvent('on' + eventName, listener);
1951        };
1952  
1953        // Remove window listeners.
1954        if (this._usePushState) {
1955          removeEventListener('popstate', this.checkUrl, false);
1956        } else if (this._useHashChange && !this.iframe) {
1957          removeEventListener('hashchange', this.checkUrl, false);
1958        }
1959  
1960        // Clean up the iframe if necessary.
1961        if (this.iframe) {
1962          document.body.removeChild(this.iframe);
1963          this.iframe = null;
1964        }
1965  
1966        // Some environments will throw when clearing an undefined interval.
1967        if (this._checkUrlInterval) clearInterval(this._checkUrlInterval);
1968        History.started = false;
1969      },
1970  
1971      // Add a route to be tested when the fragment changes. Routes added later
1972      // may override previous routes.
1973      route: function(route, callback) {
1974        this.handlers.unshift({route: route, callback: callback});
1975      },
1976  
1977      // Checks the current URL to see if it has changed, and if it has,
1978      // calls `loadUrl`, normalizing across the hidden iframe.
1979      checkUrl: function(e) {
1980        var current = this.getFragment();
1981  
1982        // If the user pressed the back button, the iframe's hash will have
1983        // changed and we should use that for comparison.
1984        if (current === this.fragment && this.iframe) {
1985          current = this.getHash(this.iframe.contentWindow);
1986        }
1987  
1988        if (current === this.fragment) {
1989          if (!this.matchRoot()) return this.notfound();
1990          return false;
1991        }
1992        if (this.iframe) this.navigate(current);
1993        this.loadUrl();
1994      },
1995  
1996      // Attempt to load the current URL fragment. If a route succeeds with a
1997      // match, returns `true`. If no defined routes matches the fragment,
1998      // returns `false`.
1999      loadUrl: function(fragment) {
2000        // If the root doesn't match, no routes can match either.
2001        if (!this.matchRoot()) return this.notfound();
2002        fragment = this.fragment = this.getFragment(fragment);
2003        return _.some(this.handlers, function(handler) {
2004          if (handler.route.test(fragment)) {
2005            handler.callback(fragment);
2006            return true;
2007          }
2008        }) || this.notfound();
2009      },
2010  
2011      // When no route could be matched, this method is called internally to
2012      // trigger the `'notfound'` event. It returns `false` so that it can be used
2013      // in tail position.
2014      notfound: function() {
2015        this.trigger('notfound');
2016        return false;
2017      },
2018  
2019      // Save a fragment into the hash history, or replace the URL state if the
2020      // 'replace' option is passed. You are responsible for properly URL-encoding
2021      // the fragment in advance.
2022      //
2023      // The options object can contain `trigger: true` if you wish to have the
2024      // route callback be fired (not usually desirable), or `replace: true`, if
2025      // you wish to modify the current URL without adding an entry to the history.
2026      navigate: function(fragment, options) {
2027        if (!History.started) return false;
2028        if (!options || options === true) options = {trigger: !!options};
2029  
2030        // Normalize the fragment.
2031        fragment = this.getFragment(fragment || '');
2032  
2033        // Strip trailing slash on the root unless _trailingSlash is true
2034        var rootPath = this.root;
2035        if (!this._trailingSlash && (fragment === '' || fragment.charAt(0) === '?')) {
2036          rootPath = rootPath.slice(0, -1) || '/';
2037        }
2038        var url = rootPath + fragment;
2039  
2040        // Strip the fragment of the query and hash for matching.
2041        fragment = fragment.replace(pathStripper, '');
2042  
2043        // Decode for matching.
2044        var decodedFragment = this.decodeFragment(fragment);
2045  
2046        if (this.fragment === decodedFragment) return;
2047        this.fragment = decodedFragment;
2048  
2049        // If pushState is available, we use it to set the fragment as a real URL.
2050        if (this._usePushState) {
2051          this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);
2052  
2053        // If hash changes haven't been explicitly disabled, update the hash
2054        // fragment to store history.
2055        } else if (this._wantsHashChange) {
2056          this._updateHash(this.location, fragment, options.replace);
2057          if (this.iframe && fragment !== this.getHash(this.iframe.contentWindow)) {
2058            var iWindow = this.iframe.contentWindow;
2059  
2060            // Opening and closing the iframe tricks IE7 and earlier to push a
2061            // history entry on hash-tag change.  When replace is true, we don't
2062            // want this.
2063            if (!options.replace) {
2064              iWindow.document.open();
2065              iWindow.document.close();
2066            }
2067  
2068            this._updateHash(iWindow.location, fragment, options.replace);
2069          }
2070  
2071        // If you've told us that you explicitly don't want fallback hashchange-
2072        // based history, then `navigate` becomes a page refresh.
2073        } else {
2074          return this.location.assign(url);
2075        }
2076        if (options.trigger) return this.loadUrl(fragment);
2077      },
2078  
2079      // Update the hash location, either replacing the current entry, or adding
2080      // a new one to the browser history.
2081      _updateHash: function(location, fragment, replace) {
2082        if (replace) {
2083          var href = location.href.replace(/(javascript:|#).*$/, '');
2084          location.replace(href + '#' + fragment);
2085        } else {
2086          // Some browsers require that `hash` contains a leading #.
2087          location.hash = '#' + fragment;
2088        }
2089      }
2090  
2091    });
2092  
2093    // Create the default Backbone.history.
2094    Backbone.history = new History;
2095  
2096    // Helpers
2097    // -------
2098  
2099    // Helper function to correctly set up the prototype chain for subclasses.
2100    // Similar to `goog.inherits`, but uses a hash of prototype properties and
2101    // class properties to be extended.
2102    var extend = function(protoProps, staticProps) {
2103      var parent = this;
2104      var child;
2105  
2106      // The constructor function for the new subclass is either defined by you
2107      // (the "constructor" property in your `extend` definition), or defaulted
2108      // by us to simply call the parent constructor.
2109      if (protoProps && _.has(protoProps, 'constructor')) {
2110        child = protoProps.constructor;
2111      } else {
2112        child = function(){ return parent.apply(this, arguments); };
2113      }
2114  
2115      // Add static properties to the constructor function, if supplied.
2116      _.extend(child, parent, staticProps);
2117  
2118      // Set the prototype chain to inherit from `parent`, without calling
2119      // `parent`'s constructor function and add the prototype properties.
2120      child.prototype = _.create(parent.prototype, protoProps);
2121      child.prototype.constructor = child;
2122  
2123      // Set a convenience property in case the parent's prototype is needed
2124      // later.
2125      child.__super__ = parent.prototype;
2126  
2127      return child;
2128    };
2129  
2130    // Set up inheritance for the model, collection, router, view and history.
2131    Model.extend = Collection.extend = Router.extend = View.extend = History.extend = extend;
2132  
2133    // Throw an error when a URL is needed, and none is supplied.
2134    var urlError = function() {
2135      throw new Error('A "url" property or function must be specified');
2136    };
2137  
2138    // Wrap an optional error callback with a fallback error event.
2139    var wrapError = function(model, options) {
2140      var error = options.error;
2141      options.error = function(resp) {
2142        if (error) error.call(options.context, model, resp, options);
2143        model.trigger('error', model, resp, options);
2144      };
2145    };
2146  
2147    // Provide useful information when things go wrong. This method is not meant
2148    // to be used directly; it merely provides the necessary introspection for the
2149    // external `debugInfo` function.
2150    Backbone._debug = function() {
2151      return {root: root, _: _};
2152    };
2153  
2154    return Backbone;
2155  });