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   1  //     Backbone.js 1.4.0
   2  
   3  //     (c) 2010-2019 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, _, $) {
  35  
  36    // Initial Setup
  37    // -------------
  38  
  39    // Save the previous value of the `Backbone` variable, so that it can be
  40    // restored later on, if `noConflict` is used.
  41    var previousBackbone = root.Backbone;
  42  
  43    // Create a local reference to a common array method we'll want to use later.
  44    var slice = Array.prototype.slice;
  45  
  46    // Current version of the library. Keep in sync with `package.json`.
  47    Backbone.VERSION = '1.4.0';
  48  
  49    // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns
  50    // the `$` 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      attrs = _.defaults(_.extend({}, defaults, attrs), defaults);
 408      this.set(attrs, options);
 409      this.changed = {};
 410      this.initialize.apply(this, arguments);
 411    };
 412  
 413    // Attach all inheritable methods to the Model prototype.
 414    _.extend(Model.prototype, Events, {
 415  
 416      // A hash of attributes whose current and previous value differ.
 417      changed: null,
 418  
 419      // The value returned during the last failed validation.
 420      validationError: null,
 421  
 422      // The default name for the JSON `id` attribute is `"id"`. MongoDB and
 423      // CouchDB users may want to set this to `"_id"`.
 424      idAttribute: 'id',
 425  
 426      // The prefix is used to create the client id which is used to identify models locally.
 427      // You may want to override this if you're experiencing name clashes with model ids.
 428      cidPrefix: 'c',
 429  
 430      // preinitialize is an empty function by default. You can override it with a function
 431      // or object.  preinitialize will run before any instantiation logic is run in the Model.
 432      preinitialize: function(){},
 433  
 434      // Initialize is an empty function by default. Override it with your own
 435      // initialization logic.
 436      initialize: function(){},
 437  
 438      // Return a copy of the model's `attributes` object.
 439      toJSON: function(options) {
 440        return _.clone(this.attributes);
 441      },
 442  
 443      // Proxy `Backbone.sync` by default -- but override this if you need
 444      // custom syncing semantics for *this* particular model.
 445      sync: function() {
 446        return Backbone.sync.apply(this, arguments);
 447      },
 448  
 449      // Get the value of an attribute.
 450      get: function(attr) {
 451        return this.attributes[attr];
 452      },
 453  
 454      // Get the HTML-escaped value of an attribute.
 455      escape: function(attr) {
 456        return _.escape(this.get(attr));
 457      },
 458  
 459      // Returns `true` if the attribute contains a value that is not null
 460      // or undefined.
 461      has: function(attr) {
 462        return this.get(attr) != null;
 463      },
 464  
 465      // Special-cased proxy to underscore's `_.matches` method.
 466      matches: function(attrs) {
 467        return !!_.iteratee(attrs, this)(this.attributes);
 468      },
 469  
 470      // Set a hash of model attributes on the object, firing `"change"`. This is
 471      // the core primitive operation of a model, updating the data and notifying
 472      // anyone who needs to know about the change in state. The heart of the beast.
 473      set: function(key, val, options) {
 474        if (key == null) return this;
 475  
 476        // Handle both `"key", value` and `{key: value}` -style arguments.
 477        var attrs;
 478        if (typeof key === 'object') {
 479          attrs = key;
 480          options = val;
 481        } else {
 482          (attrs = {})[key] = val;
 483        }
 484  
 485        options || (options = {});
 486  
 487        // Run validation.
 488        if (!this._validate(attrs, options)) return false;
 489  
 490        // Extract attributes and options.
 491        var unset      = options.unset;
 492        var silent     = options.silent;
 493        var changes    = [];
 494        var changing   = this._changing;
 495        this._changing = true;
 496  
 497        if (!changing) {
 498          this._previousAttributes = _.clone(this.attributes);
 499          this.changed = {};
 500        }
 501  
 502        var current = this.attributes;
 503        var changed = this.changed;
 504        var prev    = this._previousAttributes;
 505  
 506        // For each `set` attribute, update or delete the current value.
 507        for (var attr in attrs) {
 508          val = attrs[attr];
 509          if (!_.isEqual(current[attr], val)) changes.push(attr);
 510          if (!_.isEqual(prev[attr], val)) {
 511            changed[attr] = val;
 512          } else {
 513            delete changed[attr];
 514          }
 515          unset ? delete current[attr] : current[attr] = val;
 516        }
 517  
 518        // Update the `id`.
 519        if (this.idAttribute in attrs) this.id = this.get(this.idAttribute);
 520  
 521        // Trigger all relevant attribute changes.
 522        if (!silent) {
 523          if (changes.length) this._pending = options;
 524          for (var i = 0; i < changes.length; i++) {
 525            this.trigger('change:' + changes[i], this, current[changes[i]], options);
 526          }
 527        }
 528  
 529        // You might be wondering why there's a `while` loop here. Changes can
 530        // be recursively nested within `"change"` events.
 531        if (changing) return this;
 532        if (!silent) {
 533          while (this._pending) {
 534            options = this._pending;
 535            this._pending = false;
 536            this.trigger('change', this, options);
 537          }
 538        }
 539        this._pending = false;
 540        this._changing = false;
 541        return this;
 542      },
 543  
 544      // Remove an attribute from the model, firing `"change"`. `unset` is a noop
 545      // if the attribute doesn't exist.
 546      unset: function(attr, options) {
 547        return this.set(attr, void 0, _.extend({}, options, {unset: true}));
 548      },
 549  
 550      // Clear all attributes on the model, firing `"change"`.
 551      clear: function(options) {
 552        var attrs = {};
 553        for (var key in this.attributes) attrs[key] = void 0;
 554        return this.set(attrs, _.extend({}, options, {unset: true}));
 555      },
 556  
 557      // Determine if the model has changed since the last `"change"` event.
 558      // If you specify an attribute name, determine if that attribute has changed.
 559      hasChanged: function(attr) {
 560        if (attr == null) return !_.isEmpty(this.changed);
 561        return _.has(this.changed, attr);
 562      },
 563  
 564      // Return an object containing all the attributes that have changed, or
 565      // false if there are no changed attributes. Useful for determining what
 566      // parts of a view need to be updated and/or what attributes need to be
 567      // persisted to the server. Unset attributes will be set to undefined.
 568      // You can also pass an attributes object to diff against the model,
 569      // determining if there *would be* a change.
 570      changedAttributes: function(diff) {
 571        if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
 572        var old = this._changing ? this._previousAttributes : this.attributes;
 573        var changed = {};
 574        var hasChanged;
 575        for (var attr in diff) {
 576          var val = diff[attr];
 577          if (_.isEqual(old[attr], val)) continue;
 578          changed[attr] = val;
 579          hasChanged = true;
 580        }
 581        return hasChanged ? changed : false;
 582      },
 583  
 584      // Get the previous value of an attribute, recorded at the time the last
 585      // `"change"` event was fired.
 586      previous: function(attr) {
 587        if (attr == null || !this._previousAttributes) return null;
 588        return this._previousAttributes[attr];
 589      },
 590  
 591      // Get all of the attributes of the model at the time of the previous
 592      // `"change"` event.
 593      previousAttributes: function() {
 594        return _.clone(this._previousAttributes);
 595      },
 596  
 597      // Fetch the model from the server, merging the response with the model's
 598      // local attributes. Any changed attributes will trigger a "change" event.
 599      fetch: function(options) {
 600        options = _.extend({parse: true}, options);
 601        var model = this;
 602        var success = options.success;
 603        options.success = function(resp) {
 604          var serverAttrs = options.parse ? model.parse(resp, options) : resp;
 605          if (!model.set(serverAttrs, options)) return false;
 606          if (success) success.call(options.context, model, resp, options);
 607          model.trigger('sync', model, resp, options);
 608        };
 609        wrapError(this, options);
 610        return this.sync('read', this, options);
 611      },
 612  
 613      // Set a hash of model attributes, and sync the model to the server.
 614      // If the server returns an attributes hash that differs, the model's
 615      // state will be `set` again.
 616      save: function(key, val, options) {
 617        // Handle both `"key", value` and `{key: value}` -style arguments.
 618        var attrs;
 619        if (key == null || typeof key === 'object') {
 620          attrs = key;
 621          options = val;
 622        } else {
 623          (attrs = {})[key] = val;
 624        }
 625  
 626        options = _.extend({validate: true, parse: true}, options);
 627        var wait = options.wait;
 628  
 629        // If we're not waiting and attributes exist, save acts as
 630        // `set(attr).save(null, opts)` with validation. Otherwise, check if
 631        // the model will be valid when the attributes, if any, are set.
 632        if (attrs && !wait) {
 633          if (!this.set(attrs, options)) return false;
 634        } else if (!this._validate(attrs, options)) {
 635          return false;
 636        }
 637  
 638        // After a successful server-side save, the client is (optionally)
 639        // updated with the server-side state.
 640        var model = this;
 641        var success = options.success;
 642        var attributes = this.attributes;
 643        options.success = function(resp) {
 644          // Ensure attributes are restored during synchronous saves.
 645          model.attributes = attributes;
 646          var serverAttrs = options.parse ? model.parse(resp, options) : resp;
 647          if (wait) serverAttrs = _.extend({}, attrs, serverAttrs);
 648          if (serverAttrs && !model.set(serverAttrs, options)) return false;
 649          if (success) success.call(options.context, model, resp, options);
 650          model.trigger('sync', model, resp, options);
 651        };
 652        wrapError(this, options);
 653  
 654        // Set temporary attributes if `{wait: true}` to properly find new ids.
 655        if (attrs && wait) this.attributes = _.extend({}, attributes, attrs);
 656  
 657        var method = this.isNew() ? 'create' : options.patch ? 'patch' : 'update';
 658        if (method === 'patch' && !options.attrs) options.attrs = attrs;
 659        var xhr = this.sync(method, this, options);
 660  
 661        // Restore attributes.
 662        this.attributes = attributes;
 663  
 664        return xhr;
 665      },
 666  
 667      // Destroy this model on the server if it was already persisted.
 668      // Optimistically removes the model from its collection, if it has one.
 669      // If `wait: true` is passed, waits for the server to respond before removal.
 670      destroy: function(options) {
 671        options = options ? _.clone(options) : {};
 672        var model = this;
 673        var success = options.success;
 674        var wait = options.wait;
 675  
 676        var destroy = function() {
 677          model.stopListening();
 678          model.trigger('destroy', model, model.collection, options);
 679        };
 680  
 681        options.success = function(resp) {
 682          if (wait) destroy();
 683          if (success) success.call(options.context, model, resp, options);
 684          if (!model.isNew()) model.trigger('sync', model, resp, options);
 685        };
 686  
 687        var xhr = false;
 688        if (this.isNew()) {
 689          _.defer(options.success);
 690        } else {
 691          wrapError(this, options);
 692          xhr = this.sync('delete', this, options);
 693        }
 694        if (!wait) destroy();
 695        return xhr;
 696      },
 697  
 698      // Default URL for the model's representation on the server -- if you're
 699      // using Backbone's restful methods, override this to change the endpoint
 700      // that will be called.
 701      url: function() {
 702        var base =
 703          _.result(this, 'urlRoot') ||
 704          _.result(this.collection, 'url') ||
 705          urlError();
 706        if (this.isNew()) return base;
 707        var id = this.get(this.idAttribute);
 708        return base.replace(/[^\/]$/, '$&/') + encodeURIComponent(id);
 709      },
 710  
 711      // **parse** converts a response into the hash of attributes to be `set` on
 712      // the model. The default implementation is just to pass the response along.
 713      parse: function(resp, options) {
 714        return resp;
 715      },
 716  
 717      // Create a new model with identical attributes to this one.
 718      clone: function() {
 719        return new this.constructor(this.attributes);
 720      },
 721  
 722      // A model is new if it has never been saved to the server, and lacks an id.
 723      isNew: function() {
 724        return !this.has(this.idAttribute);
 725      },
 726  
 727      // Check if the model is currently in a valid state.
 728      isValid: function(options) {
 729        return this._validate({}, _.extend({}, options, {validate: true}));
 730      },
 731  
 732      // Run validation against the next complete set of model attributes,
 733      // returning `true` if all is well. Otherwise, fire an `"invalid"` event.
 734      _validate: function(attrs, options) {
 735        if (!options.validate || !this.validate) return true;
 736        attrs = _.extend({}, this.attributes, attrs);
 737        var error = this.validationError = this.validate(attrs, options) || null;
 738        if (!error) return true;
 739        this.trigger('invalid', this, error, _.extend(options, {validationError: error}));
 740        return false;
 741      }
 742  
 743    });
 744  
 745    // Backbone.Collection
 746    // -------------------
 747  
 748    // If models tend to represent a single row of data, a Backbone Collection is
 749    // more analogous to a table full of data ... or a small slice or page of that
 750    // table, or a collection of rows that belong together for a particular reason
 751    // -- all of the messages in this particular folder, all of the documents
 752    // belonging to this particular author, and so on. Collections maintain
 753    // indexes of their models, both in order, and for lookup by `id`.
 754  
 755    // Create a new **Collection**, perhaps to contain a specific type of `model`.
 756    // If a `comparator` is specified, the Collection will maintain
 757    // its models in sort order, as they're added and removed.
 758    var Collection = Backbone.Collection = function(models, options) {
 759      options || (options = {});
 760      this.preinitialize.apply(this, arguments);
 761      if (options.model) this.model = options.model;
 762      if (options.comparator !== void 0) this.comparator = options.comparator;
 763      this._reset();
 764      this.initialize.apply(this, arguments);
 765      if (models) this.reset(models, _.extend({silent: true}, options));
 766    };
 767  
 768    // Default options for `Collection#set`.
 769    var setOptions = {add: true, remove: true, merge: true};
 770    var addOptions = {add: true, remove: false};
 771  
 772    // Splices `insert` into `array` at index `at`.
 773    var splice = function(array, insert, at) {
 774      at = Math.min(Math.max(at, 0), array.length);
 775      var tail = Array(array.length - at);
 776      var length = insert.length;
 777      var i;
 778      for (i = 0; i < tail.length; i++) tail[i] = array[i + at];
 779      for (i = 0; i < length; i++) array[i + at] = insert[i];
 780      for (i = 0; i < tail.length; i++) array[i + length + at] = tail[i];
 781    };
 782  
 783    // Define the Collection's inheritable methods.
 784    _.extend(Collection.prototype, Events, {
 785  
 786      // The default model for a collection is just a **Backbone.Model**.
 787      // This should be overridden in most cases.
 788      model: Model,
 789  
 790  
 791      // preinitialize is an empty function by default. You can override it with a function
 792      // or object.  preinitialize will run before any instantiation logic is run in the Collection.
 793      preinitialize: function(){},
 794  
 795      // Initialize is an empty function by default. Override it with your own
 796      // initialization logic.
 797      initialize: function(){},
 798  
 799      // The JSON representation of a Collection is an array of the
 800      // models' attributes.
 801      toJSON: function(options) {
 802        return this.map(function(model) { return model.toJSON(options); });
 803      },
 804  
 805      // Proxy `Backbone.sync` by default.
 806      sync: function() {
 807        return Backbone.sync.apply(this, arguments);
 808      },
 809  
 810      // Add a model, or list of models to the set. `models` may be Backbone
 811      // Models or raw JavaScript objects to be converted to Models, or any
 812      // combination of the two.
 813      add: function(models, options) {
 814        return this.set(models, _.extend({merge: false}, options, addOptions));
 815      },
 816  
 817      // Remove a model, or a list of models from the set.
 818      remove: function(models, options) {
 819        options = _.extend({}, options);
 820        var singular = !_.isArray(models);
 821        models = singular ? [models] : models.slice();
 822        var removed = this._removeModels(models, options);
 823        if (!options.silent && removed.length) {
 824          options.changes = {added: [], merged: [], removed: removed};
 825          this.trigger('update', this, options);
 826        }
 827        return singular ? removed[0] : removed;
 828      },
 829  
 830      // Update a collection by `set`-ing a new list of models, adding new ones,
 831      // removing models that are no longer present, and merging models that
 832      // already exist in the collection, as necessary. Similar to **Model#set**,
 833      // the core operation for updating the data contained by the collection.
 834      set: function(models, options) {
 835        if (models == null) return;
 836  
 837        options = _.extend({}, setOptions, options);
 838        if (options.parse && !this._isModel(models)) {
 839          models = this.parse(models, options) || [];
 840        }
 841  
 842        var singular = !_.isArray(models);
 843        models = singular ? [models] : models.slice();
 844  
 845        var at = options.at;
 846        if (at != null) at = +at;
 847        if (at > this.length) at = this.length;
 848        if (at < 0) at += this.length + 1;
 849  
 850        var set = [];
 851        var toAdd = [];
 852        var toMerge = [];
 853        var toRemove = [];
 854        var modelMap = {};
 855  
 856        var add = options.add;
 857        var merge = options.merge;
 858        var remove = options.remove;
 859  
 860        var sort = false;
 861        var sortable = this.comparator && at == null && options.sort !== false;
 862        var sortAttr = _.isString(this.comparator) ? this.comparator : null;
 863  
 864        // Turn bare objects into model references, and prevent invalid models
 865        // from being added.
 866        var model, i;
 867        for (i = 0; i < models.length; i++) {
 868          model = models[i];
 869  
 870          // If a duplicate is found, prevent it from being added and
 871          // optionally merge it into the existing model.
 872          var existing = this.get(model);
 873          if (existing) {
 874            if (merge && model !== existing) {
 875              var attrs = this._isModel(model) ? model.attributes : model;
 876              if (options.parse) attrs = existing.parse(attrs, options);
 877              existing.set(attrs, options);
 878              toMerge.push(existing);
 879              if (sortable && !sort) sort = existing.hasChanged(sortAttr);
 880            }
 881            if (!modelMap[existing.cid]) {
 882              modelMap[existing.cid] = true;
 883              set.push(existing);
 884            }
 885            models[i] = existing;
 886  
 887          // If this is a new, valid model, push it to the `toAdd` list.
 888          } else if (add) {
 889            model = models[i] = this._prepareModel(model, options);
 890            if (model) {
 891              toAdd.push(model);
 892              this._addReference(model, options);
 893              modelMap[model.cid] = true;
 894              set.push(model);
 895            }
 896          }
 897        }
 898  
 899        // Remove stale models.
 900        if (remove) {
 901          for (i = 0; i < this.length; i++) {
 902            model = this.models[i];
 903            if (!modelMap[model.cid]) toRemove.push(model);
 904          }
 905          if (toRemove.length) this._removeModels(toRemove, options);
 906        }
 907  
 908        // See if sorting is needed, update `length` and splice in new models.
 909        var orderChanged = false;
 910        var replace = !sortable && add && remove;
 911        if (set.length && replace) {
 912          orderChanged = this.length !== set.length || _.some(this.models, function(m, index) {
 913            return m !== set[index];
 914          });
 915          this.models.length = 0;
 916          splice(this.models, set, 0);
 917          this.length = this.models.length;
 918        } else if (toAdd.length) {
 919          if (sortable) sort = true;
 920          splice(this.models, toAdd, at == null ? this.length : at);
 921          this.length = this.models.length;
 922        }
 923  
 924        // Silently sort the collection if appropriate.
 925        if (sort) this.sort({silent: true});
 926  
 927        // Unless silenced, it's time to fire all appropriate add/sort/update events.
 928        if (!options.silent) {
 929          for (i = 0; i < toAdd.length; i++) {
 930            if (at != null) options.index = at + i;
 931            model = toAdd[i];
 932            model.trigger('add', model, this, options);
 933          }
 934          if (sort || orderChanged) this.trigger('sort', this, options);
 935          if (toAdd.length || toRemove.length || toMerge.length) {
 936            options.changes = {
 937              added: toAdd,
 938              removed: toRemove,
 939              merged: toMerge
 940            };
 941            this.trigger('update', this, options);
 942          }
 943        }
 944  
 945        // Return the added (or merged) model (or models).
 946        return singular ? models[0] : models;
 947      },
 948  
 949      // When you have more items than you want to add or remove individually,
 950      // you can reset the entire set with a new list of models, without firing
 951      // any granular `add` or `remove` events. Fires `reset` when finished.
 952      // Useful for bulk operations and optimizations.
 953      reset: function(models, options) {
 954        options = options ? _.clone(options) : {};
 955        for (var i = 0; i < this.models.length; i++) {
 956          this._removeReference(this.models[i], options);
 957        }
 958        options.previousModels = this.models;
 959        this._reset();
 960        models = this.add(models, _.extend({silent: true}, options));
 961        if (!options.silent) this.trigger('reset', this, options);
 962        return models;
 963      },
 964  
 965      // Add a model to the end of the collection.
 966      push: function(model, options) {
 967        return this.add(model, _.extend({at: this.length}, options));
 968      },
 969  
 970      // Remove a model from the end of the collection.
 971      pop: function(options) {
 972        var model = this.at(this.length - 1);
 973        return this.remove(model, options);
 974      },
 975  
 976      // Add a model to the beginning of the collection.
 977      unshift: function(model, options) {
 978        return this.add(model, _.extend({at: 0}, options));
 979      },
 980  
 981      // Remove a model from the beginning of the collection.
 982      shift: function(options) {
 983        var model = this.at(0);
 984        return this.remove(model, options);
 985      },
 986  
 987      // Slice out a sub-array of models from the collection.
 988      slice: function() {
 989        return slice.apply(this.models, arguments);
 990      },
 991  
 992      // Get a model from the set by id, cid, model object with id or cid
 993      // properties, or an attributes object that is transformed through modelId.
 994      get: function(obj) {
 995        if (obj == null) return void 0;
 996        return this._byId[obj] ||
 997          this._byId[this.modelId(this._isModel(obj) ? obj.attributes : obj)] ||
 998          obj.cid && this._byId[obj.cid];
 999      },
1000  
1001      // Returns `true` if the model is in the collection.
1002      has: function(obj) {
1003        return this.get(obj) != null;
1004      },
1005  
1006      // Get the model at the given index.
1007      at: function(index) {
1008        if (index < 0) index += this.length;
1009        return this.models[index];
1010      },
1011  
1012      // Return models with matching attributes. Useful for simple cases of
1013      // `filter`.
1014      where: function(attrs, first) {
1015        return this[first ? 'find' : 'filter'](attrs);
1016      },
1017  
1018      // Return the first model with matching attributes. Useful for simple cases
1019      // of `find`.
1020      findWhere: function(attrs) {
1021        return this.where(attrs, true);
1022      },
1023  
1024      // Force the collection to re-sort itself. You don't need to call this under
1025      // normal circumstances, as the set will maintain sort order as each item
1026      // is added.
1027      sort: function(options) {
1028        var comparator = this.comparator;
1029        if (!comparator) throw new Error('Cannot sort a set without a comparator');
1030        options || (options = {});
1031  
1032        var length = comparator.length;
1033        if (_.isFunction(comparator)) comparator = comparator.bind(this);
1034  
1035        // Run sort based on type of `comparator`.
1036        if (length === 1 || _.isString(comparator)) {
1037          this.models = this.sortBy(comparator);
1038        } else {
1039          this.models.sort(comparator);
1040        }
1041        if (!options.silent) this.trigger('sort', this, options);
1042        return this;
1043      },
1044  
1045      // Pluck an attribute from each model in the collection.
1046      pluck: function(attr) {
1047        return this.map(attr + '');
1048      },
1049  
1050      // Fetch the default set of models for this collection, resetting the
1051      // collection when they arrive. If `reset: true` is passed, the response
1052      // data will be passed through the `reset` method instead of `set`.
1053      fetch: function(options) {
1054        options = _.extend({parse: true}, options);
1055        var success = options.success;
1056        var collection = this;
1057        options.success = function(resp) {
1058          var method = options.reset ? 'reset' : 'set';
1059          collection[method](resp, options);
1060          if (success) success.call(options.context, collection, resp, options);
1061          collection.trigger('sync', collection, resp, options);
1062        };
1063        wrapError(this, options);
1064        return this.sync('read', this, options);
1065      },
1066  
1067      // Create a new instance of a model in this collection. Add the model to the
1068      // collection immediately, unless `wait: true` is passed, in which case we
1069      // wait for the server to agree.
1070      create: function(model, options) {
1071        options = options ? _.clone(options) : {};
1072        var wait = options.wait;
1073        model = this._prepareModel(model, options);
1074        if (!model) return false;
1075        if (!wait) this.add(model, options);
1076        var collection = this;
1077        var success = options.success;
1078        options.success = function(m, resp, callbackOpts) {
1079          if (wait) collection.add(m, callbackOpts);
1080          if (success) success.call(callbackOpts.context, m, resp, callbackOpts);
1081        };
1082        model.save(null, options);
1083        return model;
1084      },
1085  
1086      // **parse** converts a response into a list of models to be added to the
1087      // collection. The default implementation is just to pass it through.
1088      parse: function(resp, options) {
1089        return resp;
1090      },
1091  
1092      // Create a new collection with an identical list of models as this one.
1093      clone: function() {
1094        return new this.constructor(this.models, {
1095          model: this.model,
1096          comparator: this.comparator
1097        });
1098      },
1099  
1100      // Define how to uniquely identify models in the collection.
1101      modelId: function(attrs) {
1102        return attrs[this.model.prototype.idAttribute || 'id'];
1103      },
1104  
1105      // Get an iterator of all models in this collection.
1106      values: function() {
1107        return new CollectionIterator(this, ITERATOR_VALUES);
1108      },
1109  
1110      // Get an iterator of all model IDs in this collection.
1111      keys: function() {
1112        return new CollectionIterator(this, ITERATOR_KEYS);
1113      },
1114  
1115      // Get an iterator of all [ID, model] tuples in this collection.
1116      entries: function() {
1117        return new CollectionIterator(this, ITERATOR_KEYSVALUES);
1118      },
1119  
1120      // Private method to reset all internal state. Called when the collection
1121      // is first initialized or reset.
1122      _reset: function() {
1123        this.length = 0;
1124        this.models = [];
1125        this._byId  = {};
1126      },
1127  
1128      // Prepare a hash of attributes (or other model) to be added to this
1129      // collection.
1130      _prepareModel: function(attrs, options) {
1131        if (this._isModel(attrs)) {
1132          if (!attrs.collection) attrs.collection = this;
1133          return attrs;
1134        }
1135        options = options ? _.clone(options) : {};
1136        options.collection = this;
1137        var model = new this.model(attrs, options);
1138        if (!model.validationError) return model;
1139        this.trigger('invalid', this, model.validationError, options);
1140        return false;
1141      },
1142  
1143      // Internal method called by both remove and set.
1144      _removeModels: function(models, options) {
1145        var removed = [];
1146        for (var i = 0; i < models.length; i++) {
1147          var model = this.get(models[i]);
1148          if (!model) continue;
1149  
1150          var index = this.indexOf(model);
1151          this.models.splice(index, 1);
1152          this.length--;
1153  
1154          // Remove references before triggering 'remove' event to prevent an
1155          // infinite loop. #3693
1156          delete this._byId[model.cid];
1157          var id = this.modelId(model.attributes);
1158          if (id != null) delete this._byId[id];
1159  
1160          if (!options.silent) {
1161            options.index = index;
1162            model.trigger('remove', model, this, options);
1163          }
1164  
1165          removed.push(model);
1166          this._removeReference(model, options);
1167        }
1168        return removed;
1169      },
1170  
1171      // Method for checking whether an object should be considered a model for
1172      // the purposes of adding to the collection.
1173      _isModel: function(model) {
1174        return model instanceof Model;
1175      },
1176  
1177      // Internal method to create a model's ties to a collection.
1178      _addReference: function(model, options) {
1179        this._byId[model.cid] = model;
1180        var id = this.modelId(model.attributes);
1181        if (id != null) this._byId[id] = model;
1182        model.on('all', this._onModelEvent, this);
1183      },
1184  
1185      // Internal method to sever a model's ties to a collection.
1186      _removeReference: function(model, options) {
1187        delete this._byId[model.cid];
1188        var id = this.modelId(model.attributes);
1189        if (id != null) delete this._byId[id];
1190        if (this === model.collection) delete model.collection;
1191        model.off('all', this._onModelEvent, this);
1192      },
1193  
1194      // Internal method called every time a model in the set fires an event.
1195      // Sets need to update their indexes when models change ids. All other
1196      // events simply proxy through. "add" and "remove" events that originate
1197      // in other collections are ignored.
1198      _onModelEvent: function(event, model, collection, options) {
1199        if (model) {
1200          if ((event === 'add' || event === 'remove') && collection !== this) return;
1201          if (event === 'destroy') this.remove(model, options);
1202          if (event === 'change') {
1203            var prevId = this.modelId(model.previousAttributes());
1204            var id = this.modelId(model.attributes);
1205            if (prevId !== id) {
1206              if (prevId != null) delete this._byId[prevId];
1207              if (id != null) this._byId[id] = model;
1208            }
1209          }
1210        }
1211        this.trigger.apply(this, arguments);
1212      }
1213  
1214    });
1215  
1216    // Defining an @@iterator method implements JavaScript's Iterable protocol.
1217    // In modern ES2015 browsers, this value is found at Symbol.iterator.
1218    /* global Symbol */
1219    var $$iterator = typeof Symbol === 'function' && Symbol.iterator;
1220    if ($$iterator) {
1221      Collection.prototype[$$iterator] = Collection.prototype.values;
1222    }
1223  
1224    // CollectionIterator
1225    // ------------------
1226  
1227    // A CollectionIterator implements JavaScript's Iterator protocol, allowing the
1228    // use of `for of` loops in modern browsers and interoperation between
1229    // Backbone.Collection and other JavaScript functions and third-party libraries
1230    // which can operate on Iterables.
1231    var CollectionIterator = function(collection, kind) {
1232      this._collection = collection;
1233      this._kind = kind;
1234      this._index = 0;
1235    };
1236  
1237    // This "enum" defines the three possible kinds of values which can be emitted
1238    // by a CollectionIterator that correspond to the values(), keys() and entries()
1239    // methods on Collection, respectively.
1240    var ITERATOR_VALUES = 1;
1241    var ITERATOR_KEYS = 2;
1242    var ITERATOR_KEYSVALUES = 3;
1243  
1244    // All Iterators should themselves be Iterable.
1245    if ($$iterator) {
1246      CollectionIterator.prototype[$$iterator] = function() {
1247        return this;
1248      };
1249    }
1250  
1251    CollectionIterator.prototype.next = function() {
1252      if (this._collection) {
1253  
1254        // Only continue iterating if the iterated collection is long enough.
1255        if (this._index < this._collection.length) {
1256          var model = this._collection.at(this._index);
1257          this._index++;
1258  
1259          // Construct a value depending on what kind of values should be iterated.
1260          var value;
1261          if (this._kind === ITERATOR_VALUES) {
1262            value = model;
1263          } else {
1264            var id = this._collection.modelId(model.attributes);
1265            if (this._kind === ITERATOR_KEYS) {
1266              value = id;
1267            } else { // ITERATOR_KEYSVALUES
1268              value = [id, model];
1269            }
1270          }
1271          return {value: value, done: false};
1272        }
1273  
1274        // Once exhausted, remove the reference to the collection so future
1275        // calls to the next method always return done.
1276        this._collection = void 0;
1277      }
1278  
1279      return {value: void 0, done: true};
1280    };
1281  
1282    // Backbone.View
1283    // -------------
1284  
1285    // Backbone Views are almost more convention than they are actual code. A View
1286    // is simply a JavaScript object that represents a logical chunk of UI in the
1287    // DOM. This might be a single item, an entire list, a sidebar or panel, or
1288    // even the surrounding frame which wraps your whole app. Defining a chunk of
1289    // UI as a **View** allows you to define your DOM events declaratively, without
1290    // having to worry about render order ... and makes it easy for the view to
1291    // react to specific changes in the state of your models.
1292  
1293    // Creating a Backbone.View creates its initial element outside of the DOM,
1294    // if an existing element is not provided...
1295    var View = Backbone.View = function(options) {
1296      this.cid = _.uniqueId('view');
1297      this.preinitialize.apply(this, arguments);
1298      _.extend(this, _.pick(options, viewOptions));
1299      this._ensureElement();
1300      this.initialize.apply(this, arguments);
1301    };
1302  
1303    // Cached regex to split keys for `delegate`.
1304    var delegateEventSplitter = /^(\S+)\s*(.*)$/;
1305  
1306    // List of view options to be set as properties.
1307    var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName', 'events'];
1308  
1309    // Set up all inheritable **Backbone.View** properties and methods.
1310    _.extend(View.prototype, Events, {
1311  
1312      // The default `tagName` of a View's element is `"div"`.
1313      tagName: 'div',
1314  
1315      // jQuery delegate for element lookup, scoped to DOM elements within the
1316      // current view. This should be preferred to global lookups where possible.
1317      $: function(selector) {
1318        return this.$el.find(selector);
1319      },
1320  
1321      // preinitialize is an empty function by default. You can override it with a function
1322      // or object.  preinitialize will run before any instantiation logic is run in the View
1323      preinitialize: function(){},
1324  
1325      // Initialize is an empty function by default. Override it with your own
1326      // initialization logic.
1327      initialize: function(){},
1328  
1329      // **render** is the core function that your view should override, in order
1330      // to populate its element (`this.el`), with the appropriate HTML. The
1331      // convention is for **render** to always return `this`.
1332      render: function() {
1333        return this;
1334      },
1335  
1336      // Remove this view by taking the element out of the DOM, and removing any
1337      // applicable Backbone.Events listeners.
1338      remove: function() {
1339        this._removeElement();
1340        this.stopListening();
1341        return this;
1342      },
1343  
1344      // Remove this view's element from the document and all event listeners
1345      // attached to it. Exposed for subclasses using an alternative DOM
1346      // manipulation API.
1347      _removeElement: function() {
1348        this.$el.remove();
1349      },
1350  
1351      // Change the view's element (`this.el` property) and re-delegate the
1352      // view's events on the new element.
1353      setElement: function(element) {
1354        this.undelegateEvents();
1355        this._setElement(element);
1356        this.delegateEvents();
1357        return this;
1358      },
1359  
1360      // Creates the `this.el` and `this.$el` references for this view using the
1361      // given `el`. `el` can be a CSS selector or an HTML string, a jQuery
1362      // context or an element. Subclasses can override this to utilize an
1363      // alternative DOM manipulation API and are only required to set the
1364      // `this.el` property.
1365      _setElement: function(el) {
1366        this.$el = el instanceof Backbone.$ ? el : Backbone.$(el);
1367        this.el = this.$el[0];
1368      },
1369  
1370      // Set callbacks, where `this.events` is a hash of
1371      //
1372      // *{"event selector": "callback"}*
1373      //
1374      //     {
1375      //       'mousedown .title':  'edit',
1376      //       'click .button':     'save',
1377      //       'click .open':       function(e) { ... }
1378      //     }
1379      //
1380      // pairs. Callbacks will be bound to the view, with `this` set properly.
1381      // Uses event delegation for efficiency.
1382      // Omitting the selector binds the event to `this.el`.
1383      delegateEvents: function(events) {
1384        events || (events = _.result(this, 'events'));
1385        if (!events) return this;
1386        this.undelegateEvents();
1387        for (var key in events) {
1388          var method = events[key];
1389          if (!_.isFunction(method)) method = this[method];
1390          if (!method) continue;
1391          var match = key.match(delegateEventSplitter);
1392          this.delegate(match[1], match[2], method.bind(this));
1393        }
1394        return this;
1395      },
1396  
1397      // Add a single event listener to the view's element (or a child element
1398      // using `selector`). This only works for delegate-able events: not `focus`,
1399      // `blur`, and not `change`, `submit`, and `reset` in Internet Explorer.
1400      delegate: function(eventName, selector, listener) {
1401        this.$el.on(eventName + '.delegateEvents' + this.cid, selector, listener);
1402        return this;
1403      },
1404  
1405      // Clears all callbacks previously bound to the view by `delegateEvents`.
1406      // You usually don't need to use this, but may wish to if you have multiple
1407      // Backbone views attached to the same DOM element.
1408      undelegateEvents: function() {
1409        if (this.$el) this.$el.off('.delegateEvents' + this.cid);
1410        return this;
1411      },
1412  
1413      // A finer-grained `undelegateEvents` for removing a single delegated event.
1414      // `selector` and `listener` are both optional.
1415      undelegate: function(eventName, selector, listener) {
1416        this.$el.off(eventName + '.delegateEvents' + this.cid, selector, listener);
1417        return this;
1418      },
1419  
1420      // Produces a DOM element to be assigned to your view. Exposed for
1421      // subclasses using an alternative DOM manipulation API.
1422      _createElement: function(tagName) {
1423        return document.createElement(tagName);
1424      },
1425  
1426      // Ensure that the View has a DOM element to render into.
1427      // If `this.el` is a string, pass it through `$()`, take the first
1428      // matching element, and re-assign it to `el`. Otherwise, create
1429      // an element from the `id`, `className` and `tagName` properties.
1430      _ensureElement: function() {
1431        if (!this.el) {
1432          var attrs = _.extend({}, _.result(this, 'attributes'));
1433          if (this.id) attrs.id = _.result(this, 'id');
1434          if (this.className) attrs['class'] = _.result(this, 'className');
1435          this.setElement(this._createElement(_.result(this, 'tagName')));
1436          this._setAttributes(attrs);
1437        } else {
1438          this.setElement(_.result(this, 'el'));
1439        }
1440      },
1441  
1442      // Set attributes from a hash on this view's element.  Exposed for
1443      // subclasses using an alternative DOM manipulation API.
1444      _setAttributes: function(attributes) {
1445        this.$el.attr(attributes);
1446      }
1447  
1448    });
1449  
1450    // Proxy Backbone class methods to Underscore functions, wrapping the model's
1451    // `attributes` object or collection's `models` array behind the scenes.
1452    //
1453    // collection.filter(function(model) { return model.get('age') > 10 });
1454    // collection.each(this.addView);
1455    //
1456    // `Function#apply` can be slow so we use the method's arg count, if we know it.
1457    var addMethod = function(base, length, method, attribute) {
1458      switch (length) {
1459        case 1: return function() {
1460          return base[method](this[attribute]);
1461        };
1462        case 2: return function(value) {
1463          return base[method](this[attribute], value);
1464        };
1465        case 3: return function(iteratee, context) {
1466          return base[method](this[attribute], cb(iteratee, this), context);
1467        };
1468        case 4: return function(iteratee, defaultVal, context) {
1469          return base[method](this[attribute], cb(iteratee, this), defaultVal, context);
1470        };
1471        default: return function() {
1472          var args = slice.call(arguments);
1473          args.unshift(this[attribute]);
1474          return base[method].apply(base, args);
1475        };
1476      }
1477    };
1478  
1479    var addUnderscoreMethods = function(Class, base, methods, attribute) {
1480      _.each(methods, function(length, method) {
1481        if (base[method]) Class.prototype[method] = addMethod(base, length, method, attribute);
1482      });
1483    };
1484  
1485    // Support `collection.sortBy('attr')` and `collection.findWhere({id: 1})`.
1486    var cb = function(iteratee, instance) {
1487      if (_.isFunction(iteratee)) return iteratee;
1488      if (_.isObject(iteratee) && !instance._isModel(iteratee)) return modelMatcher(iteratee);
1489      if (_.isString(iteratee)) return function(model) { return model.get(iteratee); };
1490      return iteratee;
1491    };
1492    var modelMatcher = function(attrs) {
1493      var matcher = _.matches(attrs);
1494      return function(model) {
1495        return matcher(model.attributes);
1496      };
1497    };
1498  
1499    // Underscore methods that we want to implement on the Collection.
1500    // 90% of the core usefulness of Backbone Collections is actually implemented
1501    // right here:
1502    var collectionMethods = {forEach: 3, each: 3, map: 3, collect: 3, reduce: 0,
1503      foldl: 0, inject: 0, reduceRight: 0, foldr: 0, find: 3, detect: 3, filter: 3,
1504      select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 3, includes: 3,
1505      contains: 3, invoke: 0, max: 3, min: 3, toArray: 1, size: 1, first: 3,
1506      head: 3, take: 3, initial: 3, rest: 3, tail: 3, drop: 3, last: 3,
1507      without: 0, difference: 0, indexOf: 3, shuffle: 1, lastIndexOf: 3,
1508      isEmpty: 1, chain: 1, sample: 3, partition: 3, groupBy: 3, countBy: 3,
1509      sortBy: 3, indexBy: 3, findIndex: 3, findLastIndex: 3};
1510  
1511  
1512    // Underscore methods that we want to implement on the Model, mapped to the
1513    // number of arguments they take.
1514    var modelMethods = {keys: 1, values: 1, pairs: 1, invert: 1, pick: 0,
1515      omit: 0, chain: 1, isEmpty: 1};
1516  
1517    // Mix in each Underscore method as a proxy to `Collection#models`.
1518  
1519    _.each([
1520      [Collection, collectionMethods, 'models'],
1521      [Model, modelMethods, 'attributes']
1522    ], function(config) {
1523      var Base = config[0],
1524          methods = config[1],
1525          attribute = config[2];
1526  
1527      Base.mixin = function(obj) {
1528        var mappings = _.reduce(_.functions(obj), function(memo, name) {
1529          memo[name] = 0;
1530          return memo;
1531        }, {});
1532        addUnderscoreMethods(Base, obj, mappings, attribute);
1533      };
1534  
1535      addUnderscoreMethods(Base, _, methods, attribute);
1536    });
1537  
1538    // Backbone.sync
1539    // -------------
1540  
1541    // Override this function to change the manner in which Backbone persists
1542    // models to the server. You will be passed the type of request, and the
1543    // model in question. By default, makes a RESTful Ajax request
1544    // to the model's `url()`. Some possible customizations could be:
1545    //
1546    // * Use `setTimeout` to batch rapid-fire updates into a single request.
1547    // * Send up the models as XML instead of JSON.
1548    // * Persist models via WebSockets instead of Ajax.
1549    //
1550    // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
1551    // as `POST`, with a `_method` parameter containing the true HTTP method,
1552    // as well as all requests with the body as `application/x-www-form-urlencoded`
1553    // instead of `application/json` with the model in a param named `model`.
1554    // Useful when interfacing with server-side languages like **PHP** that make
1555    // it difficult to read the body of `PUT` requests.
1556    Backbone.sync = function(method, model, options) {
1557      var type = methodMap[method];
1558  
1559      // Default options, unless specified.
1560      _.defaults(options || (options = {}), {
1561        emulateHTTP: Backbone.emulateHTTP,
1562        emulateJSON: Backbone.emulateJSON
1563      });
1564  
1565      // Default JSON-request options.
1566      var params = {type: type, dataType: 'json'};
1567  
1568      // Ensure that we have a URL.
1569      if (!options.url) {
1570        params.url = _.result(model, 'url') || urlError();
1571      }
1572  
1573      // Ensure that we have the appropriate request data.
1574      if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
1575        params.contentType = 'application/json';
1576        params.data = JSON.stringify(options.attrs || model.toJSON(options));
1577      }
1578  
1579      // For older servers, emulate JSON by encoding the request into an HTML-form.
1580      if (options.emulateJSON) {
1581        params.contentType = 'application/x-www-form-urlencoded';
1582        params.data = params.data ? {model: params.data} : {};
1583      }
1584  
1585      // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
1586      // And an `X-HTTP-Method-Override` header.
1587      if (options.emulateHTTP && (type === 'PUT' || type === 'DELETE' || type === 'PATCH')) {
1588        params.type = 'POST';
1589        if (options.emulateJSON) params.data._method = type;
1590        var beforeSend = options.beforeSend;
1591        options.beforeSend = function(xhr) {
1592          xhr.setRequestHeader('X-HTTP-Method-Override', type);
1593          if (beforeSend) return beforeSend.apply(this, arguments);
1594        };
1595      }
1596  
1597      // Don't process data on a non-GET request.
1598      if (params.type !== 'GET' && !options.emulateJSON) {
1599        params.processData = false;
1600      }
1601  
1602      // Pass along `textStatus` and `errorThrown` from jQuery.
1603      var error = options.error;
1604      options.error = function(xhr, textStatus, errorThrown) {
1605        options.textStatus = textStatus;
1606        options.errorThrown = errorThrown;
1607        if (error) error.call(options.context, xhr, textStatus, errorThrown);
1608      };
1609  
1610      // Make the request, allowing the user to override any Ajax options.
1611      var xhr = options.xhr = Backbone.ajax(_.extend(params, options));
1612      model.trigger('request', model, xhr, options);
1613      return xhr;
1614    };
1615  
1616    // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
1617    var methodMap = {
1618      create: 'POST',
1619      update: 'PUT',
1620      patch: 'PATCH',
1621      delete: 'DELETE',
1622      read: 'GET'
1623    };
1624  
1625    // Set the default implementation of `Backbone.ajax` to proxy through to `$`.
1626    // Override this if you'd like to use a different library.
1627    Backbone.ajax = function() {
1628      return Backbone.$.ajax.apply(Backbone.$, arguments);
1629    };
1630  
1631    // Backbone.Router
1632    // ---------------
1633  
1634    // Routers map faux-URLs to actions, and fire events when routes are
1635    // matched. Creating a new one sets its `routes` hash, if not set statically.
1636    var Router = Backbone.Router = function(options) {
1637      options || (options = {});
1638      this.preinitialize.apply(this, arguments);
1639      if (options.routes) this.routes = options.routes;
1640      this._bindRoutes();
1641      this.initialize.apply(this, arguments);
1642    };
1643  
1644    // Cached regular expressions for matching named param parts and splatted
1645    // parts of route strings.
1646    var optionalParam = /\((.*?)\)/g;
1647    var namedParam    = /(\(\?)?:\w+/g;
1648    var splatParam    = /\*\w+/g;
1649    var escapeRegExp  = /[\-{}\[\]+?.,\\\^$|#\s]/g;
1650  
1651    // Set up all inheritable **Backbone.Router** properties and methods.
1652    _.extend(Router.prototype, Events, {
1653  
1654      // preinitialize is an empty function by default. You can override it with a function
1655      // or object.  preinitialize will run before any instantiation logic is run in the Router.
1656      preinitialize: function(){},
1657  
1658      // Initialize is an empty function by default. Override it with your own
1659      // initialization logic.
1660      initialize: function(){},
1661  
1662      // Manually bind a single named route to a callback. For example:
1663      //
1664      //     this.route('search/:query/p:num', 'search', function(query, num) {
1665      //       ...
1666      //     });
1667      //
1668      route: function(route, name, callback) {
1669        if (!_.isRegExp(route)) route = this._routeToRegExp(route);
1670        if (_.isFunction(name)) {
1671          callback = name;
1672          name = '';
1673        }
1674        if (!callback) callback = this[name];
1675        var router = this;
1676        Backbone.history.route(route, function(fragment) {
1677          var args = router._extractParameters(route, fragment);
1678          if (router.execute(callback, args, name) !== false) {
1679            router.trigger.apply(router, ['route:' + name].concat(args));
1680            router.trigger('route', name, args);
1681            Backbone.history.trigger('route', router, name, args);
1682          }
1683        });
1684        return this;
1685      },
1686  
1687      // Execute a route handler with the provided parameters.  This is an
1688      // excellent place to do pre-route setup or post-route cleanup.
1689      execute: function(callback, args, name) {
1690        if (callback) callback.apply(this, args);
1691      },
1692  
1693      // Simple proxy to `Backbone.history` to save a fragment into the history.
1694      navigate: function(fragment, options) {
1695        Backbone.history.navigate(fragment, options);
1696        return this;
1697      },
1698  
1699      // Bind all defined routes to `Backbone.history`. We have to reverse the
1700      // order of the routes here to support behavior where the most general
1701      // routes can be defined at the bottom of the route map.
1702      _bindRoutes: function() {
1703        if (!this.routes) return;
1704        this.routes = _.result(this, 'routes');
1705        var route, routes = _.keys(this.routes);
1706        while ((route = routes.pop()) != null) {
1707          this.route(route, this.routes[route]);
1708        }
1709      },
1710  
1711      // Convert a route string into a regular expression, suitable for matching
1712      // against the current location hash.
1713      _routeToRegExp: function(route) {
1714        route = route.replace(escapeRegExp, '\\$&')
1715          .replace(optionalParam, '(?:$1)?')
1716          .replace(namedParam, function(match, optional) {
1717            return optional ? match : '([^/?]+)';
1718          })
1719          .replace(splatParam, '([^?]*?)');
1720        return new RegExp('^' + route + '(?:\\?([\\s\\S]*))?$');
1721      },
1722  
1723      // Given a route, and a URL fragment that it matches, return the array of
1724      // extracted decoded parameters. Empty or unmatched parameters will be
1725      // treated as `null` to normalize cross-browser behavior.
1726      _extractParameters: function(route, fragment) {
1727        var params = route.exec(fragment).slice(1);
1728        return _.map(params, function(param, i) {
1729          // Don't decode the search params.
1730          if (i === params.length - 1) return param || null;
1731          return param ? decodeURIComponent(param) : null;
1732        });
1733      }
1734  
1735    });
1736  
1737    // Backbone.History
1738    // ----------------
1739  
1740    // Handles cross-browser history management, based on either
1741    // [pushState](http://diveintohtml5.info/history.html) and real URLs, or
1742    // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)
1743    // and URL fragments. If the browser supports neither (old IE, natch),
1744    // falls back to polling.
1745    var History = Backbone.History = function() {
1746      this.handlers = [];
1747      this.checkUrl = this.checkUrl.bind(this);
1748  
1749      // Ensure that `History` can be used outside of the browser.
1750      if (typeof window !== 'undefined') {
1751        this.location = window.location;
1752        this.history = window.history;
1753      }
1754    };
1755  
1756    // Cached regex for stripping a leading hash/slash and trailing space.
1757    var routeStripper = /^[#\/]|\s+$/g;
1758  
1759    // Cached regex for stripping leading and trailing slashes.
1760    var rootStripper = /^\/+|\/+$/g;
1761  
1762    // Cached regex for stripping urls of hash.
1763    var pathStripper = /#.*$/;
1764  
1765    // Has the history handling already been started?
1766    History.started = false;
1767  
1768    // Set up all inheritable **Backbone.History** properties and methods.
1769    _.extend(History.prototype, Events, {
1770  
1771      // The default interval to poll for hash changes, if necessary, is
1772      // twenty times a second.
1773      interval: 50,
1774  
1775      // Are we at the app root?
1776      atRoot: function() {
1777        var path = this.location.pathname.replace(/[^\/]$/, '$&/');
1778        return path === this.root && !this.getSearch();
1779      },
1780  
1781      // Does the pathname match the root?
1782      matchRoot: function() {
1783        var path = this.decodeFragment(this.location.pathname);
1784        var rootPath = path.slice(0, this.root.length - 1) + '/';
1785        return rootPath === this.root;
1786      },
1787  
1788      // Unicode characters in `location.pathname` are percent encoded so they're
1789      // decoded for comparison. `%25` should not be decoded since it may be part
1790      // of an encoded parameter.
1791      decodeFragment: function(fragment) {
1792        return decodeURI(fragment.replace(/%25/g, '%2525'));
1793      },
1794  
1795      // In IE6, the hash fragment and search params are incorrect if the
1796      // fragment contains `?`.
1797      getSearch: function() {
1798        var match = this.location.href.replace(/#.*/, '').match(/\?.+/);
1799        return match ? match[0] : '';
1800      },
1801  
1802      // Gets the true hash value. Cannot use location.hash directly due to bug
1803      // in Firefox where location.hash will always be decoded.
1804      getHash: function(window) {
1805        var match = (window || this).location.href.match(/#(.*)$/);
1806        return match ? match[1] : '';
1807      },
1808  
1809      // Get the pathname and search params, without the root.
1810      getPath: function() {
1811        var path = this.decodeFragment(
1812          this.location.pathname + this.getSearch()
1813        ).slice(this.root.length - 1);
1814        return path.charAt(0) === '/' ? path.slice(1) : path;
1815      },
1816  
1817      // Get the cross-browser normalized URL fragment from the path or hash.
1818      getFragment: function(fragment) {
1819        if (fragment == null) {
1820          if (this._usePushState || !this._wantsHashChange) {
1821            fragment = this.getPath();
1822          } else {
1823            fragment = this.getHash();
1824          }
1825        }
1826        return fragment.replace(routeStripper, '');
1827      },
1828  
1829      // Start the hash change handling, returning `true` if the current URL matches
1830      // an existing route, and `false` otherwise.
1831      start: function(options) {
1832        if (History.started) throw new Error('Backbone.history has already been started');
1833        History.started = true;
1834  
1835        // Figure out the initial configuration. Do we need an iframe?
1836        // Is pushState desired ... is it available?
1837        this.options          = _.extend({root: '/'}, this.options, options);
1838        this.root             = this.options.root;
1839        this._wantsHashChange = this.options.hashChange !== false;
1840        this._hasHashChange   = 'onhashchange' in window && (document.documentMode === void 0 || document.documentMode > 7);
1841        this._useHashChange   = this._wantsHashChange && this._hasHashChange;
1842        this._wantsPushState  = !!this.options.pushState;
1843        this._hasPushState    = !!(this.history && this.history.pushState);
1844        this._usePushState    = this._wantsPushState && this._hasPushState;
1845        this.fragment         = this.getFragment();
1846  
1847        // Normalize root to always include a leading and trailing slash.
1848        this.root = ('/' + this.root + '/').replace(rootStripper, '/');
1849  
1850        // Transition from hashChange to pushState or vice versa if both are
1851        // requested.
1852        if (this._wantsHashChange && this._wantsPushState) {
1853  
1854          // If we've started off with a route from a `pushState`-enabled
1855          // browser, but we're currently in a browser that doesn't support it...
1856          if (!this._hasPushState && !this.atRoot()) {
1857            var rootPath = this.root.slice(0, -1) || '/';
1858            this.location.replace(rootPath + '#' + this.getPath());
1859            // Return immediately as browser will do redirect to new url
1860            return true;
1861  
1862          // Or if we've started out with a hash-based route, but we're currently
1863          // in a browser where it could be `pushState`-based instead...
1864          } else if (this._hasPushState && this.atRoot()) {
1865            this.navigate(this.getHash(), {replace: true});
1866          }
1867  
1868        }
1869  
1870        // Proxy an iframe to handle location events if the browser doesn't
1871        // support the `hashchange` event, HTML5 history, or the user wants
1872        // `hashChange` but not `pushState`.
1873        if (!this._hasHashChange && this._wantsHashChange && !this._usePushState) {
1874          this.iframe = document.createElement('iframe');
1875          this.iframe.src = 'javascript:0';
1876          this.iframe.style.display = 'none';
1877          this.iframe.tabIndex = -1;
1878          var body = document.body;
1879          // Using `appendChild` will throw on IE < 9 if the document is not ready.
1880          var iWindow = body.insertBefore(this.iframe, body.firstChild).contentWindow;
1881          iWindow.document.open();
1882          iWindow.document.close();
1883          iWindow.location.hash = '#' + this.fragment;
1884        }
1885  
1886        // Add a cross-platform `addEventListener` shim for older browsers.
1887        var addEventListener = window.addEventListener || function(eventName, listener) {
1888          return attachEvent('on' + eventName, listener);
1889        };
1890  
1891        // Depending on whether we're using pushState or hashes, and whether
1892        // 'onhashchange' is supported, determine how we check the URL state.
1893        if (this._usePushState) {
1894          addEventListener('popstate', this.checkUrl, false);
1895        } else if (this._useHashChange && !this.iframe) {
1896          addEventListener('hashchange', this.checkUrl, false);
1897        } else if (this._wantsHashChange) {
1898          this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
1899        }
1900  
1901        if (!this.options.silent) return this.loadUrl();
1902      },
1903  
1904      // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
1905      // but possibly useful for unit testing Routers.
1906      stop: function() {
1907        // Add a cross-platform `removeEventListener` shim for older browsers.
1908        var removeEventListener = window.removeEventListener || function(eventName, listener) {
1909          return detachEvent('on' + eventName, listener);
1910        };
1911  
1912        // Remove window listeners.
1913        if (this._usePushState) {
1914          removeEventListener('popstate', this.checkUrl, false);
1915        } else if (this._useHashChange && !this.iframe) {
1916          removeEventListener('hashchange', this.checkUrl, false);
1917        }
1918  
1919        // Clean up the iframe if necessary.
1920        if (this.iframe) {
1921          document.body.removeChild(this.iframe);
1922          this.iframe = null;
1923        }
1924  
1925        // Some environments will throw when clearing an undefined interval.
1926        if (this._checkUrlInterval) clearInterval(this._checkUrlInterval);
1927        History.started = false;
1928      },
1929  
1930      // Add a route to be tested when the fragment changes. Routes added later
1931      // may override previous routes.
1932      route: function(route, callback) {
1933        this.handlers.unshift({route: route, callback: callback});
1934      },
1935  
1936      // Checks the current URL to see if it has changed, and if it has,
1937      // calls `loadUrl`, normalizing across the hidden iframe.
1938      checkUrl: function(e) {
1939        var current = this.getFragment();
1940  
1941        // If the user pressed the back button, the iframe's hash will have
1942        // changed and we should use that for comparison.
1943        if (current === this.fragment && this.iframe) {
1944          current = this.getHash(this.iframe.contentWindow);
1945        }
1946  
1947        if (current === this.fragment) return false;
1948        if (this.iframe) this.navigate(current);
1949        this.loadUrl();
1950      },
1951  
1952      // Attempt to load the current URL fragment. If a route succeeds with a
1953      // match, returns `true`. If no defined routes matches the fragment,
1954      // returns `false`.
1955      loadUrl: function(fragment) {
1956        // If the root doesn't match, no routes can match either.
1957        if (!this.matchRoot()) return false;
1958        fragment = this.fragment = this.getFragment(fragment);
1959        return _.some(this.handlers, function(handler) {
1960          if (handler.route.test(fragment)) {
1961            handler.callback(fragment);
1962            return true;
1963          }
1964        });
1965      },
1966  
1967      // Save a fragment into the hash history, or replace the URL state if the
1968      // 'replace' option is passed. You are responsible for properly URL-encoding
1969      // the fragment in advance.
1970      //
1971      // The options object can contain `trigger: true` if you wish to have the
1972      // route callback be fired (not usually desirable), or `replace: true`, if
1973      // you wish to modify the current URL without adding an entry to the history.
1974      navigate: function(fragment, options) {
1975        if (!History.started) return false;
1976        if (!options || options === true) options = {trigger: !!options};
1977  
1978        // Normalize the fragment.
1979        fragment = this.getFragment(fragment || '');
1980  
1981        // Don't include a trailing slash on the root.
1982        var rootPath = this.root;
1983        if (fragment === '' || fragment.charAt(0) === '?') {
1984          rootPath = rootPath.slice(0, -1) || '/';
1985        }
1986        var url = rootPath + fragment;
1987  
1988        // Strip the fragment of the query and hash for matching.
1989        fragment = fragment.replace(pathStripper, '');
1990  
1991        // Decode for matching.
1992        var decodedFragment = this.decodeFragment(fragment);
1993  
1994        if (this.fragment === decodedFragment) return;
1995        this.fragment = decodedFragment;
1996  
1997        // If pushState is available, we use it to set the fragment as a real URL.
1998        if (this._usePushState) {
1999          this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);
2000  
2001        // If hash changes haven't been explicitly disabled, update the hash
2002        // fragment to store history.
2003        } else if (this._wantsHashChange) {
2004          this._updateHash(this.location, fragment, options.replace);
2005          if (this.iframe && fragment !== this.getHash(this.iframe.contentWindow)) {
2006            var iWindow = this.iframe.contentWindow;
2007  
2008            // Opening and closing the iframe tricks IE7 and earlier to push a
2009            // history entry on hash-tag change.  When replace is true, we don't
2010            // want this.
2011            if (!options.replace) {
2012              iWindow.document.open();
2013              iWindow.document.close();
2014            }
2015  
2016            this._updateHash(iWindow.location, fragment, options.replace);
2017          }
2018  
2019        // If you've told us that you explicitly don't want fallback hashchange-
2020        // based history, then `navigate` becomes a page refresh.
2021        } else {
2022          return this.location.assign(url);
2023        }
2024        if (options.trigger) return this.loadUrl(fragment);
2025      },
2026  
2027      // Update the hash location, either replacing the current entry, or adding
2028      // a new one to the browser history.
2029      _updateHash: function(location, fragment, replace) {
2030        if (replace) {
2031          var href = location.href.replace(/(javascript:|#).*$/, '');
2032          location.replace(href + '#' + fragment);
2033        } else {
2034          // Some browsers require that `hash` contains a leading #.
2035          location.hash = '#' + fragment;
2036        }
2037      }
2038  
2039    });
2040  
2041    // Create the default Backbone.history.
2042    Backbone.history = new History;
2043  
2044    // Helpers
2045    // -------
2046  
2047    // Helper function to correctly set up the prototype chain for subclasses.
2048    // Similar to `goog.inherits`, but uses a hash of prototype properties and
2049    // class properties to be extended.
2050    var extend = function(protoProps, staticProps) {
2051      var parent = this;
2052      var child;
2053  
2054      // The constructor function for the new subclass is either defined by you
2055      // (the "constructor" property in your `extend` definition), or defaulted
2056      // by us to simply call the parent constructor.
2057      if (protoProps && _.has(protoProps, 'constructor')) {
2058        child = protoProps.constructor;
2059      } else {
2060        child = function(){ return parent.apply(this, arguments); };
2061      }
2062  
2063      // Add static properties to the constructor function, if supplied.
2064      _.extend(child, parent, staticProps);
2065  
2066      // Set the prototype chain to inherit from `parent`, without calling
2067      // `parent`'s constructor function and add the prototype properties.
2068      child.prototype = _.create(parent.prototype, protoProps);
2069      child.prototype.constructor = child;
2070  
2071      // Set a convenience property in case the parent's prototype is needed
2072      // later.
2073      child.__super__ = parent.prototype;
2074  
2075      return child;
2076    };
2077  
2078    // Set up inheritance for the model, collection, router, view and history.
2079    Model.extend = Collection.extend = Router.extend = View.extend = History.extend = extend;
2080  
2081    // Throw an error when a URL is needed, and none is supplied.
2082    var urlError = function() {
2083      throw new Error('A "url" property or function must be specified');
2084    };
2085  
2086    // Wrap an optional error callback with a fallback error event.
2087    var wrapError = function(model, options) {
2088      var error = options.error;
2089      options.error = function(resp) {
2090        if (error) error.call(options.context, model, resp, options);
2091        model.trigger('error', model, resp, options);
2092      };
2093    };
2094  
2095    return Backbone;
2096  });


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