backbone 学习之全部源码

完整的Backbone.js源码分析：

//     Backbone.js 1.0.0



//     (c) 2010-2013 Jeremy Ashkenas, DocumentCloud Inc.

//     Backbone may be freely distributed under the MIT license.

//     For all details and documentation:

//     http://backbonejs.org



(function(){



  // Initial Setup

  // -------------



  // Save a reference to the global object (`window` in the browser, `exports`

  // on the server).

  var root = this;



  // Save the previous value of the `Backbone` variable, so that it can be

  // restored later on, if `noConflict` is used.

  var previousBackbone = root.Backbone;



  // Create local references to array methods we'll want to use later.

  var array = [];

  var push = array.push;

  var slice = array.slice;

  var splice = array.splice;



  // The top-level namespace. All public Backbone classes and modules will

  // be attached to this. Exported for both the browser and the server.

  var Backbone;

  if (typeof exports !== 'undefined') {

    Backbone = exports;

  } else {

    Backbone = root.Backbone = {};

  }



  // Current version of the library. Keep in sync with `package.json`.

  Backbone.VERSION = '1.0.0';



  // Require Underscore, if we're on the server, and it's not already present.

  var _ = root._;

  if (!_ && (typeof require !== 'undefined')) _ = require('underscore');



  // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns

  // the `$` variable.

  Backbone.$ = root.jQuery || root.Zepto || root.ender || root.$;



  // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable

  // to its previous owner. Returns a reference to this Backbone object.

  Backbone.noConflict = function() {

    root.Backbone = previousBackbone;

    return this;

  };



  // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option

  // will fake `"PUT"` and `"DELETE"` requests via the `_method` parameter and

  // set a `X-Http-Method-Override` header.

  Backbone.emulateHTTP = false;



  // Turn on `emulateJSON` to support legacy servers that can't deal with direct

  // `application/json` requests ... will encode the body as

  // `application/x-www-form-urlencoded` instead and will send the model in a

  // form param named `model`.

  Backbone.emulateJSON = false;



  // Backbone.Events

  // ---------------



  // A module that can be mixed in to *any object* in order to provide it with

  // custom events. You may bind with `on` or remove with `off` callback

  // functions to an event; `trigger`-ing an event fires all callbacks in

  // succession.

  //

  //     var object = {};

  //     _.extend(object, Backbone.Events);

  //     object.on('expand', function(){ alert('expanded'); });

  //     object.trigger('expand');

  //

  var Events = Backbone.Events = {



    // Bind an event to a `callback` function. Passing `"all"` will bind

    // the callback to all events fired.

    // 绑定事件 name: 事件名 callback：回调函数 context：回调函数执行时的this

    on: function(name, callback, context) {

      // 如果是jquery式的事件绑定（'blur change' {blur: .. change: ..}） 或者没有callback 直接返回

      if (!eventsApi(this, 'on', name, [callback, context]) || !callback) return this;

      this._events || (this._events = {});

      var events = this._events[name] || (this._events[name] = []);

      events.push({callback: callback, context: context, ctx: context || this});

      return this;

    },



    // Bind an event to only be triggered a single time. After the first time

    // the callback is invoked, it will be removed.

    // 确保只是被触发一次

    once: function(name, callback, context) {

      if (!eventsApi(this, 'once', name, [callback, context]) || !callback) return this;

      var self = this;

      var once = _.once(function() {

        self.off(name, once);

        callback.apply(this, arguments);

      });

      once._callback = callback;

      return this.on(name, once, context);

    },



    // Remove one or many callbacks. If `context` is null, removes all

    // callbacks with that function. If `callback` is null, removes all

    // callbacks for the event. If `name` is null, removes all bound

    // callbacks for all events.

    // 移除绑定事件

    off: function(name, callback, context) {

      var retain, ev, events, names, i, l, j, k;

      if (!this._events || !eventsApi(this, 'off', name, [callback, context])) return this;

      if (!name && !callback && !context) {

        this._events = {};

        return this;

      }



      // 如果有name, 那么就尝试移除指定的事件 否则话就移除所有的事件

      names = name ? [name] : _.keys(this._events);

      for (i = 0, l = names.length; i < l; i++) {

        name = names[i];

        if (events = this._events[name]) {

          this._events[name] = retain = [];

          // 如果有callback 或者 context 需要判断是否相同

          // 相同则移除 不同的话就不移除

          if (callback || context) {

            for (j = 0, k = events.length; j < k; j++) {

              ev = events[j];

              if ((callback && callback !== ev.callback && callback !== ev.callback._callback) ||

                  (context && context !== ev.context)) {

                retain.push(ev);

              }

            }

          }

          // 如果没有任何的监听处理程序 就删除

          if (!retain.length) delete this._events[name];

        }

      }



      return this;

    },



    // Trigger one or many events, firing all bound callbacks. Callbacks are

    // passed the same arguments as `trigger` is, apart from the event name

    // (unless you're listening on `"all"`, which will cause your callback to

    // receive the true name of the event as the first argument).

    // 触发某类事件 name：事件名 后面可以跟其他参数

    trigger: function(name) {

      if (!this._events) return this;

      var args = slice.call(arguments, 1);

      if (!eventsApi(this, 'trigger', name, args)) return this;

      var events = this._events[name];

      var allEvents = this._events.all;

      if (events) triggerEvents(events, args);

      if (allEvents) triggerEvents(allEvents, arguments);

      return this;

    },



    // Tell this object to stop listening to either specific events ... or

    // to every object it's currently listening to.

    // 停止监听对象obj的执行name的callback事件

    stopListening: function(obj, name, callback) {

      var listeners = this._listeners;

      if (!listeners) return this;

      var deleteListener = !name && !callback;

      if (typeof name === 'object') callback = this;

      if (obj) (listeners = {})[obj._listenerId] = obj;

      for (var id in listeners) {

        listeners[id].off(name, callback, this);

        if (deleteListener) delete this._listeners[id];

      }

      return this;

    }



  };



  // Regular expression used to split event strings.

  var eventSplitter = /\s+/;



  // Implement fancy features of the Events API such as multiple event

  // names `"change blur"` and jQuery-style event maps `{change: action}`

  // in terms of the existing API.

  // `"change blur"` `{change: action}` 这两种类型的jquery式事件处理

  var eventsApi = function(obj, action, name, rest) {

    if (!name) return true;



    // Handle event maps.

    if (typeof name === 'object') {

      for (var key in name) {

        obj[action].apply(obj, [key, name[key]].concat(rest));

      }

      return false;

    }



    // Handle space separated event names.

    if (eventSplitter.test(name)) {

      var names = name.split(eventSplitter);

      for (var i = 0, l = names.length; i < l; i++) {

        obj[action].apply(obj, [names[i]].concat(rest));

      }

      return false;

    }



    return true;

  };



  // A difficult-to-believe, but optimized internal dispatch function for

  // triggering events. Tries to keep the usual cases speedy (most internal

  // Backbone events have 3 arguments).

  // 方便触发事件时 传给 事件处理函数 的参数问题

  var triggerEvents = function(events, args) {

    var ev, i = -1, l = events.length, a1 = args[0], a2 = args[1], a3 = args[2];

    switch (args.length) {

      case 0: while (++i < l) (ev = events[i]).callback.call(ev.ctx); return;

      case 1: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1); return;

      case 2: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2); return;

      case 3: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2, a3); return;

      default: while (++i < l) (ev = events[i]).callback.apply(ev.ctx, args);

    }

  };



  var listenMethods = {listenTo: 'on', listenToOnce: 'once'};



  // Inversion-of-control versions of `on` and `once`. Tell *this* object to

  // listen to an event in another object ... keeping track of what it's

  // listening to.

  // 告知当前对象监听另一个对象obj的某个事件 用于跟踪obj的事件

  // 也就是当obj的name类型的事件触发的时候，就会执行当前对象

  // 追踪的这个callback

  _.each(listenMethods, function(implementation, method) {

    Events[method] = function(obj, name, callback) {

      var listeners = this._listeners || (this._listeners = {});

      var id = obj._listenerId || (obj._listenerId = _.uniqueId('l'));

      listeners[id] = obj;

      if (typeof name === 'object') callback = this;

      obj[implementation](name, callback, this);

      return this;

    };

  });



  // Aliases for backwards compatibility.

  Events.bind   = Events.on;

  Events.unbind = Events.off;



  // Allow the `Backbone` object to serve as a global event bus, for folks who

  // want global "pubsub" in a convenient place.

  _.extend(Backbone, Events);



  // Backbone.Model

  // --------------



  // Backbone **Models** are the basic data object in the framework --

  // frequently representing a row in a table in a database on your server.

  // A discrete chunk of data and a bunch of useful, related methods for

  // performing computations and transformations on that data.



  // Create a new model with the specified attributes. A client id (`cid`)

  // is automatically generated and assigned for you.

  var Model = Backbone.Model = function(attributes, options) {

    var defaults;

    var attrs = attributes || {}; // 数据

    options || (options = {}); // 配置的可选项

    this.cid = _.uniqueId('c'); // 每一个model都有一个cid属性 方便collection

                                // 可以根据cid得到当前model

    this.attributes = {};

    // 如果options指定了 url urlRoot 和 collection的话就添加到this上

    _.extend(this, _.pick(options, modelOptions)); 

    // 如果有parse解析数据的函数的话 就处理数据

    if (options.parse) attrs = this.parse(attrs, options) || {};

    // 存在defaults默认信息，有的话就给attrs设置上

    if (defaults = _.result(this, 'defaults')) {

      attrs = _.defaults({}, attrs, defaults);

    }

    this.set(attrs, options);

    this.changed = {};// 记录当前model有那些东西更改了

    this.initialize.apply(this, arguments); // 初始化

  };



  // A list of options to be attached directly to the model, if provided.

  var modelOptions = ['url', 'urlRoot', 'collection'];



  // Attach all inheritable methods to the Model prototype.

  _.extend(Model.prototype, Events, {



    // A hash of attributes whose current and previous value differ.

    changed: null,



    // The value returned during the last failed validation.

    validationError: null,



    // The default name for the JSON `id` attribute is `"id"`. MongoDB and

    // CouchDB users may want to set this to `"_id"`.

    // 数据的id属性值是什么 默认id

    idAttribute: 'id',



    // Initialize is an empty function by default. Override it with your own

    // initialization logic.

    initialize: function(){},



    // Return a copy of the model's `attributes` object.

    // 得到新的对象

    toJSON: function(options) {

      return _.clone(this.attributes);

    },



    // Proxy `Backbone.sync` by default -- but override this if you need

    // custom syncing semantics for *this* particular model.

    // 请求

    sync: function() {

      return Backbone.sync.apply(this, arguments);

    },



    // Get the value of an attribute.

    // 得到数据attr属性信息

    get: function(attr) {

      return this.attributes[attr];

    },



    // Get the HTML-escaped value of an attribute.

    // 转义数据attr属性信息

    escape: function(attr) {

      return _.escape(this.get(attr));

    },



    // Returns `true` if the attribute contains a value that is not null

    // or undefined.

    has: function(attr) {

      return this.get(attr) != null;

    },



    // Set a hash of model attributes on the object, firing `"change"`. This is

    // the core primitive operation of a model, updating the data and notifying

    // anyone who needs to know about the change in state. The heart of the beast.

    // model的核心操作 在这里会触发change事件

    set: function(key, val, options) {

      var attr, attrs, unset, changes, silent, changing, prev, current;

      if (key == null) return this;



      // Handle both `"key", value` and `{key: value}` -style arguments.

      if (typeof key === 'object') {

        attrs = key;

        options = val;

      } else {

        (attrs = {})[key] = val;

      }



      options || (options = {});



      // Run validation.

      // 验证数据合法性

      if (!this._validate(attrs, options)) return false;



      // Extract attributes and options.

      unset           = options.unset; // 设置数据 || 全部设置undefined 

      silent          = options.silent; // 静悄悄？ 是否触发change事件

      changes         = []; // 所有的改变数据集合

      changing        = this._changing; // 是否已经在改变

      this._changing  = true;



      if (!changing) {

        this._previousAttributes = _.clone(this.attributes); // 为改变之前的数据

        this.changed = {};

      }

      current = this.attributes, prev = this._previousAttributes;



      // Check for changes of `id`.

      if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];



      // For each `set` attribute, update or delete the current value.

      // 更新或者删除当前要设置的值 并记录改变属性值

      for (attr in attrs) {

        val = attrs[attr];

        if (!_.isEqual(current[attr], val)) changes.push(attr);

        if (!_.isEqual(prev[attr], val)) {

          this.changed[attr] = val;

        } else {

          delete this.changed[attr];

        }

        unset ? delete current[attr] : current[attr] = val;

      }



      // Trigger all relevant attribute changes.

      if (!silent) {

        if (changes.length) this._pending = true; // 如果有某些属性改变 触发change

        for (var i = 0, l = changes.length; i < l; i++) {

          this.trigger('change:' + changes[i], this, current[changes[i]], options);

        }

      }



      // You might be wondering why there's a `while` loop here. Changes can

      // be recursively nested within `"change"` events.

      // 避免change的递归嵌套问题

      if (changing) return this;

      if (!silent) {

        while (this._pending) {

          this._pending = false;

          this.trigger('change', this, options);

        }

      }

      this._pending = false;

      this._changing = false;

      return this;

    },



    // Remove an attribute from the model, firing `"change"`. `unset` is a noop

    // if the attribute doesn't exist.

    // 移除数据中的某属性值

    unset: function(attr, options) {

      return this.set(attr, void 0, _.extend({}, options, {unset: true}));

    },



    // Clear all attributes on the model, firing `"change"`.

    // 清楚所有数据 触发change事件

    clear: function(options) {

      var attrs = {};

      for (var key in this.attributes) attrs[key] = void 0;

      return this.set(attrs, _.extend({}, options, {unset: true}));

    },



    // Determine if the model has changed since the last `"change"` event.

    // If you specify an attribute name, determine if that attribute has changed.

    // 是否有数据发生改变 || 某个属性是否发生了改变

    hasChanged: function(attr) {

      if (attr == null) return !_.isEmpty(this.changed);

      return _.has(this.changed, attr);

    },



    // Return an object containing all the attributes that have changed, or

    // false if there are no changed attributes. Useful for determining what

    // parts of a view need to be updated and/or what attributes need to be

    // persisted to the server. Unset attributes will be set to undefined.

    // You can also pass an attributes object to diff against the model,

    // determining if there *would be* a change.

    // 得到改变的属性信息

    changedAttributes: function(diff) {

      if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;

      var val, changed = false;

      var old = this._changing ? this._previousAttributes : this.attributes;

      for (var attr in diff) {

        if (_.isEqual(old[attr], (val = diff[attr]))) continue;

        (changed || (changed = {}))[attr] = val;

      }

      return changed;

    },



    // Get the previous value of an attribute, recorded at the time the last

    // `"change"` event was fired.

    // 在change之前的上一次数据

    previous: function(attr) {

      if (attr == null || !this._previousAttributes) return null;

      return this._previousAttributes[attr];

    },



    // Get all of the attributes of the model at the time of the previous

    // `"change"` event.

    previousAttributes: function() {

      return _.clone(this._previousAttributes);

    },



    // Fetch the model from the server. If the server's representation of the

    // model differs from its current attributes, they will be overridden,

    // triggering a `"change"` event.

    // 取得所有数据 请求

    // 成功的时候会触发change事件

    fetch: function(options) {

      options = options ? _.clone(options) : {};

      if (options.parse === void 0) options.parse = true;

      var model = this;

      var success = options.success;

      options.success = function(resp) {

        if (!model.set(model.parse(resp, options), options)) return false;

        if (success) success(model, resp, options);

        model.trigger('sync', model, resp, options);

      };

      wrapError(this, options);

      return this.sync('read', this, options);

    },



    // Set a hash of model attributes, and sync the model to the server.

    // If the server returns an attributes hash that differs, the model's

    // state will be `set` again.

    // 保存数据到服务端 可能是创建 或者 删除 更改等

    save: function(key, val, options) {

      var attrs, method, xhr, attributes = this.attributes;



      // Handle both `"key", value` and `{key: value}` -style arguments.

      if (key == null || typeof key === 'object') {

        attrs = key;

        options = val;

      } else {

        (attrs = {})[key] = val;

      }



      // If we're not waiting and attributes exist, save acts as `set(attr).save(null, opts)`.

      if (attrs && (!options || !options.wait) && !this.set(attrs, options)) return false;



      options = _.extend({validate: true}, options);



      // Do not persist invalid models.

      if (!this._validate(attrs, options)) return false;



      // Set temporary attributes if `{wait: true}`.

      if (attrs && options.wait) {

        this.attributes = _.extend({}, attributes, attrs);

      }



      // After a successful server-side save, the client is (optionally)

      // updated with the server-side state.

      if (options.parse === void 0) options.parse = true;

      var model = this;

      var success = options.success;

      options.success = function(resp) {

        // Ensure attributes are restored during synchronous saves.

        model.attributes = attributes;

        var serverAttrs = model.parse(resp, options);

        if (options.wait) serverAttrs = _.extend(attrs || {}, serverAttrs);

        if (_.isObject(serverAttrs) && !model.set(serverAttrs, options)) {

          return false;

        }

        if (success) success(model, resp, options);

        model.trigger('sync', model, resp, options);

      };

      wrapError(this, options);



      method = this.isNew() ? 'create' : (options.patch ? 'patch' : 'update');

      if (method === 'patch') options.attrs = attrs;

      xhr = this.sync(method, this, options);



      // Restore attributes.

      if (attrs && options.wait) this.attributes = attributes;



      return xhr;

    },



    // Destroy this model on the server if it was already persisted.

    // Optimistically removes the model from its collection, if it has one.

    // If `wait: true` is passed, waits for the server to respond before removal.

    // 销毁 删除 服务端同步更新 触发destroy事件

    destroy: function(options) {

      options = options ? _.clone(options) : {};

      var model = this;

      var success = options.success;



      var destroy = function() {

        model.trigger('destroy', model, model.collection, options);

      };



      options.success = function(resp) {

        if (options.wait || model.isNew()) destroy();

        if (success) success(model, resp, options);

        if (!model.isNew()) model.trigger('sync', model, resp, options);

      };



      if (this.isNew()) {

        options.success();

        return false;

      }

      wrapError(this, options);



      var xhr = this.sync('delete', this, options);

      if (!options.wait) destroy();

      return xhr;

    },



    // Default URL for the model's representation on the server -- if you're

    // using Backbone's restful methods, override this to change the endpoint

    // that will be called.

    // 此model请求的url

    url: function() {

      var base = _.result(this, 'urlRoot') || _.result(this.collection, 'url') || urlError();

      if (this.isNew()) return base;

      return base + (base.charAt(base.length - 1) === '/' ? '' : '/') + encodeURIComponent(this.id);

    },



    // **parse** converts a response into the hash of attributes to be `set` on

    // the model. The default implementation is just to pass the response along.

    // 解析数据的函数 做一些操作什么的

    parse: function(resp, options) {

      return resp;

    },



    // Create a new model with identical attributes to this one.

    clone: function() {

      return new this.constructor(this.attributes);

    },



    // A model is new if it has never been saved to the server, and lacks an id.

    // 此model是否保存到服务端过 没有的话就认为是新的 通过的是判断id

    isNew: function() {

      return this.id == null;

    },



    // Check if the model is currently in a valid state.

    isValid: function(options) {

      return this._validate({}, _.extend(options || {}, { validate: true }));

    },



    // Run validation against the next complete set of model attributes,

    // returning `true` if all is well. Otherwise, fire an `"invalid"` event.

    // 验证函数validate 是否会验证成功 失败的话会触发invalid事件

    _validate: function(attrs, options) {

      if (!options.validate || !this.validate) return true;

      attrs = _.extend({}, this.attributes, attrs);

      var error = this.validationError = this.validate(attrs, options) || null;

      if (!error) return true;

      this.trigger('invalid', this, error, _.extend(options || {}, {validationError: error}));

      return false;

    }



  });



  // Underscore methods that we want to implement on the Model.

  var modelMethods = ['keys', 'values', 'pairs', 'invert', 'pick', 'omit'];



  // Mix in each Underscore method as a proxy to `Model#attributes`.

  _.each(modelMethods, function(method) {

    Model.prototype[method] = function() {

      var args = slice.call(arguments);

      args.unshift(this.attributes);

      return _[method].apply(_, args);

    };

  });



  // Backbone.Collection

  // -------------------



  // If models tend to represent a single row of data, a Backbone Collection is

  // more analagous to a table full of data ... or a small slice or page of that

  // table, or a collection of rows that belong together for a particular reason

  // -- all of the messages in this particular folder, all of the documents

  // belonging to this particular author, and so on. Collections maintain

  // indexes of their models, both in order, and for lookup by `id`.



  // Create a new **Collection**, perhaps to contain a specific type of `model`.

  // If a `comparator` is specified, the Collection will maintain

  // its models in sort order, as they're added and removed.

  var Collection = Backbone.Collection = function(models, options) {

    options || (options = {});

    if (options.url) this.url = options.url;

    if (options.model) this.model = options.model; // 某一类型Model

    // 如果设置了comparator，那么就会根据comparator对collection中的models进行排序

    if (options.comparator !== void 0) this.comparator = options.comparator;

    this._reset();// 重置

    this.initialize.apply(this, arguments);

    if (models) this.reset(models, _.extend({silent: true}, options));

  };



  // Default options for `Collection#set`.

  var setOptions = {add: true, remove: true, merge: true};

  var addOptions = {add: true, merge: false, remove: false};



  // Define the Collection's inheritable methods.

  _.extend(Collection.prototype, Events, {



    // The default model for a collection is just a **Backbone.Model**.

    // This should be overridden in most cases.

    // 默认model集合就是Backbone.Model实例的集合

    model: Model,



    // Initialize is an empty function by default. Override it with your own

    // initialization logic.

    initialize: function(){},



    // The JSON representation of a Collection is an array of the

    // models' attributes.

    toJSON: function(options) {

      return this.map(function(model){ return model.toJSON(options); });

    },



    // Proxy `Backbone.sync` by default.

    sync: function() {

      return Backbone.sync.apply(this, arguments);

    },



    // Add a model, or list of models to the set.

    // 增加一个model或者model集合

    add: function(models, options) {

      return this.set(models, _.defaults(options || {}, addOptions));

    },



    // Remove a model, or a list of models from the set.

    // 移除一个model或者model集合

    // 会触发model的remove事件

    remove: function(models, options) {

      models = _.isArray(models) ? models.slice() : [models];

      options || (options = {});

      var i, l, index, model;

      for (i = 0, l = models.length; i < l; i++) {

        model = this.get(models[i]);

        if (!model) continue;

        delete this._byId[model.id];

        delete this._byId[model.cid];

        index = this.indexOf(model);

        this.models.splice(index, 1);

        this.length--;

        if (!options.silent) {

          options.index = index;

          model.trigger('remove', model, this, options);

        }

        this._removeReference(model);

      }

      return this;

    },



    // Update a collection by `set`-ing a new list of models, adding new ones,

    // removing models that are no longer present, and merging models that

    // already exist in the collection, as necessary. Similar to **Model#set**,

    // the core operation for updating the data contained by the collection.

    // 更新这个collection的models集合

    set: function(models, options) {

      options = _.defaults(options || {}, setOptions);

      if (options.parse) models = this.parse(models, options);

      if (!_.isArray(models)) models = models ? [models] : [];

      var i, l, model, attrs, existing, sort;

      var at = options.at;

      var sortable = this.comparator && (at == null) && options.sort !== false;

      var sortAttr = _.isString(this.comparator) ? this.comparator : null;

      var toAdd = [], toRemove = [], modelMap = {};



      // Turn bare objects into model references, and prevent invalid models

      // from being added.

      for (i = 0, l = models.length; i < l; i++) {

        // 检查是否是Model的实例 并且查看此model是否设置了collection属性

        // 没的话就设置成this当前的collection

        if (!(model = this._prepareModel(models[i], options))) continue;



        // If a duplicate is found, prevent it from being added and

        // optionally merge it into the existing model.

        // 如果已经存在此model

        // 如果存在 那么看是否是移除 还是合并

        if (existing = this.get(model)) {

          if (options.remove) modelMap[existing.cid] = true;

          if (options.merge) {

            existing.set(model.attributes, options);

            if (sortable && !sort && existing.hasChanged(sortAttr)) sort = true;

          }



        // This is a new model, push it to the `toAdd` list.

        } else if (options.add) {

          toAdd.push(model);



          // Listen to added models' events, and index models for lookup by

          // `id` and by `cid`.

          // 监听model的all事件

          model.on('all', this._onModelEvent, this);

          this._byId[model.cid] = model; // 方便根据id得到model

          if (model.id != null) this._byId[model.id] = model;

        }

      }



      // Remove nonexistent models if appropriate.

      if (options.remove) {

        for (i = 0, l = this.length; i < l; ++i) {

          if (!modelMap[(model = this.models[i]).cid]) toRemove.push(model);

        }

        if (toRemove.length) this.remove(toRemove, options);

      }



      // See if sorting is needed, update `length` and splice in new models.

      // 是否需要排序 增加或者插入新增的models

      if (toAdd.length) {

        if (sortable) sort = true;

        this.length += toAdd.length;

        if (at != null) {

          splice.apply(this.models, [at, 0].concat(toAdd));

        } else {

          push.apply(this.models, toAdd);

        }

      }



      // Silently sort the collection if appropriate.

      // 排序

      if (sort) this.sort({silent: true});



      if (options.silent) return this;



      // Trigger `add` events.

      // 触发model的add事件

      for (i = 0, l = toAdd.length; i < l; i++) {

        (model = toAdd[i]).trigger('add', model, this, options);

      }

      

      // Trigger `sort` if the collection was sorted.

      // 触发collection的sort事件

      if (sort) this.trigger('sort', this, options);

      return this;

    },



    // When you have more items than you want to add or remove individually,

    // you can reset the entire set with a new list of models, without firing

    // any granular `add` or `remove` events. Fires `reset` when finished.

    // Useful for bulk operations and optimizations.

    // 重置models 记录上次的models

    // 触发collection的reset事件

    reset: function(models, options) {

      options || (options = {});

      for (var i = 0, l = this.models.length; i < l; i++) {

        this._removeReference(this.models[i]);

      }

      options.previousModels = this.models;

      this._reset();

      this.add(models, _.extend({silent: true}, options));

      if (!options.silent) this.trigger('reset', this, options);

      return this;

    },



    // Add a model to the end of the collection.

    // 在最后新增一个model

    push: function(model, options) {

      model = this._prepareModel(model, options);

      this.add(model, _.extend({at: this.length}, options));

      return model;

    },



    // Remove a model from the end of the collection.

    // 移除最后一个model

    pop: function(options) {

      var model = this.at(this.length - 1);

      this.remove(model, options);

      return model;

    },



    // Add a model to the beginning of the collection.

    // 在开始的位置增加一个model

    unshift: function(model, options) {

      model = this._prepareModel(model, options);

      this.add(model, _.extend({at: 0}, options));

      return model;

    },



    // Remove a model from the beginning of the collection.

    // 移除collection的第一个model

    shift: function(options) {

      var model = this.at(0);

      this.remove(model, options);

      return model;

    },



    // Slice out a sub-array of models from the collection.

    // 得到collection中的从begin位置到end位置的所有的model

    slice: function(begin, end) {

      return this.models.slice(begin, end);

    },



    // Get a model from the set by id.

    get: function(obj) {

      if (obj == null) return void 0;

      return this._byId[obj.id != null ? obj.id : obj.cid || obj];

    },



    // Get the model at the given index.

    at: function(index) {

      return this.models[index];

    },



    // Return models with matching attributes. Useful for simple cases of

    // `filter`.

    // 返回符合attrs的models 

    // first是否只要第一个符合的

    where: function(attrs, first) {

      if (_.isEmpty(attrs)) return first ? void 0 : [];

      return this[first ? 'find' : 'filter'](function(model) {

        for (var key in attrs) {

          if (attrs[key] !== model.get(key)) return false;

        }

        return true;

      });

    },



    // Return the first model with matching attributes. Useful for simple cases

    // of `find`.

    findWhere: function(attrs) {

      return this.where(attrs, true);

    },



    // Force the collection to re-sort itself. You don't need to call this under

    // normal circumstances, as the set will maintain sort order as each item

    // is added.

    // 对collection进行排序（根据comparator）

    // 触发集合的sort事件

    sort: function(options) {

      if (!this.comparator) throw new Error('Cannot sort a set without a comparator');

      options || (options = {});



      // Run sort based on type of `comparator`.

      // comparator是string或者长度是1

      if (_.isString(this.comparator) || this.comparator.length === 1) {

        this.models = this.sortBy(this.comparator, this);

      } else {// 函数

        this.models.sort(_.bind(this.comparator, this));

      }



      if (!options.silent) this.trigger('sort', this, options);

      return this;

    },



    // Figure out the smallest index at which a model should be inserted so as

    // to maintain order.

    // model在collection中排序后的位置

    sortedIndex: function(model, value, context) {

      value || (value = this.comparator);

      var iterator = _.isFunction(value) ? value : function(model) {

        return model.get(value);

      };

      return _.sortedIndex(this.models, model, iterator, context);

    },



    // Pluck an attribute from each model in the collection.

    // 从集合中的每个模型拉取 attribute

    pluck: function(attr) {

      return _.invoke(this.models, 'get', attr);

    },



    // Fetch the default set of models for this collection, resetting the

    // collection when they arrive. If `reset: true` is passed, the response

    // data will be passed through the `reset` method instead of `set`.

    // 从服务器端请求默认集合的模型

    // 成功后会 set或者reset 集合

    // 会触发read事件

    fetch: function(options) {

      options = options ? _.clone(options) : {};

      if (options.parse === void 0) options.parse = true;

      var success = options.success;

      var collection = this;

      options.success = function(resp) {

        var method = options.reset ? 'reset' : 'set';

        collection[method](resp, options);

        if (success) success(collection, resp, options);

        collection.trigger('sync', collection, resp, options);

      };

      wrapError(this, options);

      return this.sync('read', this, options);

    },



    // Create a new instance of a model in this collection. Add the model to the

    // collection immediately, unless `wait: true` is passed, in which case we

    // wait for the server to agree.

    // 从collection中创建一个model 可能的话会直接加入到collection中

    create: function(model, options) {

      options = options ? _.clone(options) : {};

      if (!(model = this._prepareModel(model, options))) return false;

      if (!options.wait) this.add(model, options);

      var collection = this;

      var success = options.success;

      options.success = function(resp) {

        if (options.wait) collection.add(model, options);

        if (success) success(model, resp, options);

      };

      model.save(null, options);

      return model;

    },



    // **parse** converts a response into a list of models to be added to the

    // collection. The default implementation is just to pass it through.

    parse: function(resp, options) {

      return resp;

    },



    // Create a new collection with an identical list of models as this one.

    clone: function() {

      return new this.constructor(this.models);

    },



    // Private method to reset all internal state. Called when the collection

    // is first initialized or reset.

    _reset: function() {

      this.length = 0;

      this.models = [];

      this._byId  = {};

    },



    // Prepare a hash of attributes (or other model) to be added to this

    // collection.

    // 判断attrs是否是Model实例

    // 并且查看此model是否设置了collection属性

    _prepareModel: function(attrs, options) {

      if (attrs instanceof Model) {

        if (!attrs.collection) attrs.collection = this;// 指定model的collection指向this collection

        return attrs;

      }

      options || (options = {});

      options.collection = this;

      var model = new this.model(attrs, options);

      if (!model._validate(attrs, options)) {

        this.trigger('invalid', this, attrs, options);

        return false;

      }

      return model;

    },



    // Internal method to sever a model's ties to a collection.

    // 移除model监听的all事件

    _removeReference: function(model) {

      if (this === model.collection) delete model.collection;

      model.off('all', this._onModelEvent, this);

    },



    // Internal method called every time a model in the set fires an event.

    // Sets need to update their indexes when models change ids. All other

    // events simply proxy through. "add" and "remove" events that originate

    // in other collections are ignored.

    // 当前集合中的model发生改变的时候就会执行此函数

    _onModelEvent: function(event, model, collection, options) {

      if ((event === 'add' || event === 'remove') && collection !== this) return;

      if (event === 'destroy') this.remove(model, options);

      if (model && event === 'change:' + model.idAttribute) {

        delete this._byId[model.previous(model.idAttribute)];

        if (model.id != null) this._byId[model.id] = model;

      }

      this.trigger.apply(this, arguments);

    }



  });



  // Underscore methods that we want to implement on the Collection.

  // 90% of the core usefulness of Backbone Collections is actually implemented

  // right here:

  var methods = ['forEach', 'each', 'map', 'collect', 'reduce', 'foldl',

    'inject', 'reduceRight', 'foldr', 'find', 'detect', 'filter', 'select',

    'reject', 'every', 'all', 'some', 'any', 'include', 'contains', 'invoke',

    'max', 'min', 'toArray', 'size', 'first', 'head', 'take', 'initial', 'rest',

    'tail', 'drop', 'last', 'without', 'indexOf', 'shuffle', 'lastIndexOf',

    'isEmpty', 'chain'];



  // Mix in each Underscore method as a proxy to `Collection#models`.

  // 丰富collection的方法

  _.each(methods, function(method) {

    Collection.prototype[method] = function() {

      var args = slice.call(arguments);

      args.unshift(this.models);

      return _[method].apply(_, args);

    };

  });



  // Underscore methods that take a property name as an argument.

  var attributeMethods = ['groupBy', 'countBy', 'sortBy'];



  // Use attributes instead of properties.

  _.each(attributeMethods, function(method) {

    Collection.prototype[method] = function(value, context) {

      var iterator = _.isFunction(value) ? value : function(model) {

        return model.get(value);

      };

      return _[method](this.models, iterator, context);

    };

  });



  // Backbone.View

  // -------------



  // Backbone Views are almost more convention than they are actual code. A View

  // is simply a JavaScript object that represents a logical chunk of UI in the

  // DOM. This might be a single item, an entire list, a sidebar or panel, or

  // even the surrounding frame which wraps your whole app. Defining a chunk of

  // UI as a **View** allows you to define your DOM events declaratively, without

  // having to worry about render order ... and makes it easy for the view to

  // react to specific changes in the state of your models.



  // Creating a Backbone.View creates its initial element outside of the DOM,

  // if an existing element is not provided...

  var View = Backbone.View = function(options) {

    this.cid = _.uniqueId('view');

    this._configure(options || {});

    this._ensureElement(); // 确保el

    this.initialize.apply(this, arguments);

    this.delegateEvents(); // 绑定事件

  };



  // Cached regex to split keys for `delegate`.

  var delegateEventSplitter = /^(\S+)\s*(.*)$/;



  // List of view options to be merged as properties.

  // view中的关键属性

  var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName', 'events'];



  // Set up all inheritable **Backbone.View** properties and methods.

  _.extend(View.prototype, Events, {



    // The default `tagName` of a View's element is `"div"`.

    // view 的tagName 在没有设置el的时候，默认view的内容的容器就是div

    tagName: 'div',



    // jQuery delegate for element lookup, scoped to DOM elements within the

    // current view. This should be prefered to global lookups where possible.

    // 查找元素

    $: function(selector) {

      return this.$el.find(selector);

    },



    // Initialize is an empty function by default. Override it with your own

    // initialization logic.

    initialize: function(){},



    // **render** is the core function that your view should override, in order

    // to populate its element (`this.el`), with the appropriate HTML. The

    // convention is for **render** to always return `this`.

    // 渲染函数 一般需要重写

    render: function() {

      return this;

    },



    // Remove this view by taking the element out of the DOM, and removing any

    // applicable Backbone.Events listeners.

    // 移除元素

    remove: function() {

      this.$el.remove();

      this.stopListening();

      return this;

    },



    // Change the view's element (`this.el` property), including event

    // re-delegation.

    // 设置元素

    setElement: function(element, delegate) {

      if (this.$el) this.undelegateEvents(); // 解绑 释放内存

      this.$el = element instanceof Backbone.$ ? element : Backbone.$(element);

      this.el = this.$el[0];

      if (delegate !== false) this.delegateEvents();

      return this;

    },



    // Set callbacks, where `this.events` is a hash of

    //

    // *{"event selector": "callback"}*

    //

    //     {

    //       'mousedown .title':  'edit',

    //       'click .button':     'save'

    //       'click .open':       function(e) { ... }

    //     }

    //

    // pairs. Callbacks will be bound to the view, with `this` set properly.

    // Uses event delegation for efficiency.

    // Omitting the selector binds the event to `this.el`.

    // This only works for delegate-able events: not `focus`, `blur`, and

    // not `change`, `submit`, and `reset` in Internet Explorer.

    // 根据键值对来绑定事件

    delegateEvents: function(events) {

      if (!(events || (events = _.result(this, 'events')))) return this;

      this.undelegateEvents();

      for (var key in events) {

        var method = events[key];

        if (!_.isFunction(method)) method = this[events[key]];

        if (!method) continue;



        var match = key.match(delegateEventSplitter);

        var eventName = match[1], selector = match[2];

        method = _.bind(method, this);

        eventName += '.delegateEvents' + this.cid;

        if (selector === '') {

          this.$el.on(eventName, method);

        } else {

          this.$el.on(eventName, selector, method);

        }

      }

      return this;

    },



    // Clears all callbacks previously bound to the view with `delegateEvents`.

    // You usually don't need to use this, but may wish to if you have multiple

    // Backbone views attached to the same DOM element.

    // 解绑事件

    undelegateEvents: function() {

      this.$el.off('.delegateEvents' + this.cid);

      return this;

    },



    // Performs the initial configuration of a View with a set of options.

    // Keys with special meaning *(e.g. model, collection, id, className)* are

    // attached directly to the view.  See `viewOptions` for an exhaustive

    // list.

    // 配置options中的viewOptions中的项到this上

    _configure: function(options) {

      if (this.options) options = _.extend({}, _.result(this, 'options'), options);

      _.extend(this, _.pick(options, viewOptions)); // 拓展this

      this.options = options;

    },



    // Ensure that the View has a DOM element to render into.

    // If `this.el` is a string, pass it through `$()`, take the first

    // matching element, and re-assign it to `el`. Otherwise, create

    // an element from the `id`, `className` and `tagName` properties.

    // 确保有el $el

    _ensureElement: function() {

      if (!this.el) {

        var attrs = _.extend({}, _.result(this, 'attributes')); // options中的attributes

        if (this.id) attrs.id = _.result(this, 'id'); // id

        if (this.className) attrs['class'] = _.result(this, 'className');

        var $el = Backbone.$('<' + _.result(this, 'tagName') + '>').attr(attrs);

        this.setElement($el, false);

      } else {

        this.setElement(_.result(this, 'el'), false);

      }

    }



  });



  // Backbone.sync

  // -------------



  // Override this function to change the manner in which Backbone persists

  // models to the server. You will be passed the type of request, and the

  // model in question. By default, makes a RESTful Ajax request

  // to the model's `url()`. Some possible customizations could be:

  //

  // * Use `setTimeout` to batch rapid-fire updates into a single request.

  // * Send up the models as XML instead of JSON.

  // * Persist models via WebSockets instead of Ajax.

  //

  // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests

  // as `POST`, with a `_method` parameter containing the true HTTP method,

  // as well as all requests with the body as `application/x-www-form-urlencoded`

  // instead of `application/json` with the model in a param named `model`.

  // Useful when interfacing with server-side languages like **PHP** that make

  // it difficult to read the body of `PUT` requests.

  Backbone.sync = function(method, model, options) {

    var type = methodMap[method];



    // Default options, unless specified.

    _.defaults(options || (options = {}), {

      emulateHTTP: Backbone.emulateHTTP,

      emulateJSON: Backbone.emulateJSON

    });



    // Default JSON-request options.

    var params = {type: type, dataType: 'json'};



    // Ensure that we have a URL.

    // 确保有url 没在option中的话 从model获取

    if (!options.url) {

      params.url = _.result(model, 'url') || urlError();

    }



    // Ensure that we have the appropriate request data.

    if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {

      params.contentType = 'application/json';

      params.data = JSON.stringify(options.attrs || model.toJSON(options));

    }



    // For older servers, emulate JSON by encoding the request into an HTML-form.

    if (options.emulateJSON) {

      params.contentType = 'application/x-www-form-urlencoded';

      params.data = params.data ? {model: params.data} : {};

    }



    // For older servers, emulate HTTP by mimicking the HTTP method with `_method`

    // And an `X-HTTP-Method-Override` header.

    if (options.emulateHTTP && (type === 'PUT' || type === 'DELETE' || type === 'PATCH')) {

      params.type = 'POST';

      if (options.emulateJSON) params.data._method = type;

      // 在请求之前需要做的处理

      var beforeSend = options.beforeSend;

      options.beforeSend = function(xhr) {

        xhr.setRequestHeader('X-HTTP-Method-Override', type);

        if (beforeSend) return beforeSend.apply(this, arguments);

      };

    }



    // Don't process data on a non-GET request.

    if (params.type !== 'GET' && !options.emulateJSON) {

      params.processData = false;

    }



    // If we're sending a `PATCH` request, and we're in an old Internet Explorer

    // that still has ActiveX enabled by default, override jQuery to use that

    // for XHR instead. Remove this line when jQuery supports `PATCH` on IE8.

    // 兼容jquery的patch请求

    if (params.type === 'PATCH' && window.ActiveXObject &&

          !(window.external && window.external.msActiveXFilteringEnabled)) {

      params.xhr = function() {

        return new ActiveXObject("Microsoft.XMLHTTP");

      };

    }



    // Make the request, allowing the user to override any Ajax options.

    var xhr = options.xhr = Backbone.ajax(_.extend(params, options));

    model.trigger('request', model, xhr, options);// 触发request请求

    return xhr;

  };



  // Map from CRUD to HTTP for our default `Backbone.sync` implementation.

  var methodMap = {

    'create': 'POST',

    'update': 'PUT',

    'patch':  'PATCH',

    'delete': 'DELETE',

    'read':   'GET'

  };



  // Set the default implementation of `Backbone.ajax` to proxy through to `$`.

  // Override this if you'd like to use a different library.

  // 默认jquery zepto的ajax请求

  Backbone.ajax = function() {

    return Backbone.$.ajax.apply(Backbone.$, arguments);

  };



  // Backbone.Router

  // ---------------



  // Routers map faux-URLs to actions, and fire events when routes are

  // matched. Creating a new one sets its `routes` hash, if not set statically.

  var Router = Backbone.Router = function(options) {

    options || (options = {});

    if (options.routes) this.routes = options.routes;// 键值对式的导航规则 映射到处理函数上

    this._bindRoutes();

    this.initialize.apply(this, arguments);

  };



  // Cached regular expressions for matching named param parts and splatted

  // parts of route strings.

  var optionalParam = /\((.*?)\)/g;

  var namedParam    = /(\(\?)?:\w+/g;

  var splatParam    = /\*\w+/g;

  var escapeRegExp  = /[\-{}\[\]+?.,\\\^$|#\s]/g;



  // Set up all inheritable **Backbone.Router** properties and methods.

  _.extend(Router.prototype, Events, {



    // Initialize is an empty function by default. Override it with your own

    // initialization logic.

    initialize: function(){},



    // Manually bind a single named route to a callback. For example:

    //

    //     this.route('search/:query/p:num', 'search', function(query, num) {

    //       ...

    //     });

    // 导航 指定路由规则 和routes的效果相同 规则也一样

    route: function(route, name, callback) {

      if (!_.isRegExp(route)) route = this._routeToRegExp(route); // 规则验证

      if (_.isFunction(name)) {

        callback = name;

        name = '';

      }

      if (!callback) callback = this[name];

      var router = this;

      Backbone.history.route(route, function(fragment) {

        var args = router._extractParameters(route, fragment);

        callback && callback.apply(router, args);

        router.trigger.apply(router, ['route:' + name].concat(args));

        // 触发router的route事件

        router.trigger('route', name, args);

        // 触发history的route事件

        Backbone.history.trigger('route', router, name, args);

      });

      return this;

    },



    // Simple proxy to `Backbone.history` to save a fragment into the history.

    navigate: function(fragment, options) {

      Backbone.history.navigate(fragment, options);

      return this;

    },



    // Bind all defined routes to `Backbone.history`. We have to reverse the

    // order of the routes here to support behavior where the most general

    // routes can be defined at the bottom of the route map.

    // 绑定所有的routes

    _bindRoutes: function() {

      if (!this.routes) return;

      this.routes = _.result(this, 'routes');

      var route, routes = _.keys(this.routes);

      while ((route = routes.pop()) != null) {

        this.route(route, this.routes[route]);

      }

    },



    // Convert a route string into a regular expression, suitable for matching

    // against the current location hash.

    // 将route字符串转成正则表达式 

    _routeToRegExp: function(route) {

      route = route.replace(escapeRegExp, '\\$&') // 将 - { } [ ] + ? . , \ ^ $ # 空格 等进行转义

                   .replace(optionalParam, '(?:$1)?') // 规则中的括号部分 也就是可有可没有的部分

                   .replace(namedParam, function(match, optional){ // 将不带括号部分的 但是:...形式的进行替换可以匹配为非/以外任意字符

                     return optional ? match : '([^\/]+)';

                   })// 

                   .replace(splatParam, '(.*?)');// 将*...形式的替换为除换行以外的任何字符匹配.*

      return new RegExp('^' + route + '$'); // 构建正则 加上 开始^和结束$

    },



    // Given a route, and a URL fragment that it matches, return the array of

    // extracted decoded parameters. Empty or unmatched parameters will be

    // treated as `null` to normalize cross-browser behavior.

    // 返回decode后的一些URL信息（通过和route匹配的fragment做处理）

    _extractParameters: function(route, fragment) {

      var params = route.exec(fragment).slice(1);

      return _.map(params, function(param) {

        return param ? decodeURIComponent(param) : null;

      });

    }



  });



  // Backbone.History

  // ----------------



  // Handles cross-browser history management, based on either

  // [pushState](http://diveintohtml5.info/history.html) and real URLs, or

  // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)

  // and URL fragments. If the browser supports neither (old IE, natch),

  // falls back to polling.

  var History = Backbone.History = function() {

    this.handlers = [];

    _.bindAll(this, 'checkUrl');



    // Ensure that `History` can be used outside of the browser.

    if (typeof window !== 'undefined') {

      this.location = window.location;

      this.history = window.history;

    }

  };



  // Cached regex for stripping a leading hash/slash and trailing space.

  var routeStripper = /^[#\/]|\s+$/g;



  // Cached regex for stripping leading and trailing slashes.

  var rootStripper = /^\/+|\/+$/g;



  // Cached regex for detecting MSIE.

  var isExplorer = /msie [\w.]+/;



  // Cached regex for removing a trailing slash.

  var trailingSlash = /\/$/;



  // Has the history handling already been started?

  History.started = false;



  // Set up all inheritable **Backbone.History** properties and methods.

  _.extend(History.prototype, Events, {



    // The default interval to poll for hash changes, if necessary, is

    // twenty times a second.

    // hash更改的事件间隔 针对旧式浏览器

    interval: 50,



    // Gets the true hash value. Cannot use location.hash directly due to bug

    // in Firefox where location.hash will always be decoded.

    // firefox取hash的bug

    getHash: function(window) {

      var match = (window || this).location.href.match(/#(.*)$/);

      return match ? match[1] : '';

    },



    // Get the cross-browser normalized URL fragment, either from the URL,

    // the hash, or the override.

    // 跨浏览器的得到URL片段 不管是URL hash 或其他

    getFragment: function(fragment, forcePushState) {

      if (fragment == null) {

        if (this._hasPushState || !this._wantsHashChange || forcePushState) {

          fragment = this.location.pathname;

          var root = this.root.replace(trailingSlash, '');

          if (!fragment.indexOf(root)) fragment = fragment.substr(root.length);

        } else {

          fragment = this.getHash();

        }

      }

      return fragment.replace(routeStripper, '');

    },



    // Start the hash change handling, returning `true` if the current URL matches

    // an existing route, and `false` otherwise.

    // 开始监听hash change事件（兼容性）

    start: function(options) {

      if (History.started) throw new Error("Backbone.history has already been started");

      History.started = true;



      // Figure out the initial configuration. Do we need an iframe?

      // Is pushState desired ... is it available?

      this.options          = _.extend({}, {root: '/'}, this.options, options);

      this.root             = this.options.root;

      this._wantsHashChange = this.options.hashChange !== false;

      this._wantsPushState  = !!this.options.pushState;// 是否采用popstate修改地址栏地址

      this._hasPushState    = !!(this.options.pushState && this.history && this.history.pushState);// 支持popstate

      var fragment          = this.getFragment();

      var docMode           = document.documentMode;

      // 老版本ie

      var oldIE             = (isExplorer.exec(navigator.userAgent.toLowerCase()) && (!docMode || docMode <= 7));



      // Normalize root to always include a leading and trailing slash.

      this.root = ('/' + this.root + '/').replace(rootStripper, '/');

      // 老版本ie的兼容性方案

      // 利用iframe来做

      if (oldIE && this._wantsHashChange) {

        this.iframe = Backbone.$('<iframe src="javascript:0" tabindex="-1" />').hide().appendTo('body')[0].contentWindow;

        this.navigate(fragment);

      }



      // Depending on whether we're using pushState or hashes, and whether

      // 'onhashchange' is supported, determine how we check the URL state.

      // 支持popstate 就监听popstate

      // 支持hashchange 就监听hashchange

      // 否则的话只能每隔一段时间进行检测了

      if (this._hasPushState) {

        Backbone.$(window).on('popstate', this.checkUrl);

      } else if (this._wantsHashChange && ('onhashchange' in window) && !oldIE) {

        Backbone.$(window).on('hashchange', this.checkUrl);

      } else if (this._wantsHashChange) {

        this._checkUrlInterval = setInterval(this.checkUrl, this.interval);

      }



      // Determine if we need to change the base url, for a pushState link

      // opened by a non-pushState browser.

      this.fragment = fragment;

      var loc = this.location;

      var atRoot = loc.pathname.replace(/[^\/]$/, '$&/') === this.root;



      // If we've started off with a route from a `pushState`-enabled browser,

      // but we're currently in a browser that doesn't support it...

      // 兼容性处理 参数设置与当前浏览器支持情况冲突的时候

      if (this._wantsHashChange && this._wantsPushState && !this._hasPushState && !atRoot) {

        this.fragment = this.getFragment(null, true);

        this.location.replace(this.root + this.location.search + '#' + this.fragment);

        // Return immediately as browser will do redirect to new url

        return true;



      // Or if we've started out with a hash-based route, but we're currently

      // in a browser where it could be `pushState`-based instead...

      } else if (this._wantsPushState && this._hasPushState && atRoot && loc.hash) {

        this.fragment = this.getHash().replace(routeStripper, '');

        this.history.replaceState({}, document.title, this.root + this.fragment + loc.search);

      }



      if (!this.options.silent) return this.loadUrl();

    },



    // Disable Backbone.history, perhaps temporarily. Not useful in a real app,

    // but possibly useful for unit testing Routers.

    // 停止历史支持

    stop: function() {

      Backbone.$(window).off('popstate', this.checkUrl).off('hashchange', this.checkUrl);

      clearInterval(this._checkUrlInterval);

      History.started = false;

    },



    // Add a route to be tested when the fragment changes. Routes added later

    // may override previous routes.

    // 导航到相应的route地址

    // 这里用handlers队列处理， 防止快速的改变地址但是没处理完成 引起的问题

    route: function(route, callback) {

      this.handlers.unshift({route: route, callback: callback});

    },



    // Checks the current URL to see if it has changed, and if it has,

    // calls `loadUrl`, normalizing across the hidden iframe.

    // 检查url 兼容性处理

    checkUrl: function(e) {

      var current = this.getFragment();

      if (current === this.fragment && this.iframe) {

        current = this.getFragment(this.getHash(this.iframe));

      }

      if (current === this.fragment) return false;

      if (this.iframe) this.navigate(current);

      this.loadUrl() || this.loadUrl(this.getHash());

    },



    // Attempt to load the current URL fragment. If a route succeeds with a

    // match, returns `true`. If no defined routes matches the fragment,

    // returns `false`.

    // load当前的URL片段 如果真的有相应的route地址处理函数 则执行它

    loadUrl: function(fragmentOverride) {

      var fragment = this.fragment = this.getFragment(fragmentOverride);

      var matched = _.any(this.handlers, function(handler) {

        if (handler.route.test(fragment)) {

          handler.callback(fragment);

          return true;

        }

      });

      return matched;

    },



    // Save a fragment into the hash history, or replace the URL state if the

    // 'replace' option is passed. You are responsible for properly URL-encoding

    // the fragment in advance.

    //

    // The options object can contain `trigger: true` if you wish to have the

    // route callback be fired (not usually desirable), or `replace: true`, if

    // you wish to modify the current URL without adding an entry to the history.

    // 导航 根据url片段导航去相应的画面 兼容性处理

    navigate: function(fragment, options) {

      if (!History.started) return false;

      if (!options || options === true) options = {trigger: options};

      fragment = this.getFragment(fragment || '');

      if (this.fragment === fragment) return;

      this.fragment = fragment;

      var url = this.root + fragment;



      // If pushState is available, we use it to set the fragment as a real URL.

      if (this._hasPushState) {

        this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);



      // If hash changes haven't been explicitly disabled, update the hash

      // fragment to store history.

      } else if (this._wantsHashChange) {

        this._updateHash(this.location, fragment, options.replace);

        if (this.iframe && (fragment !== this.getFragment(this.getHash(this.iframe)))) {

          // Opening and closing the iframe tricks IE7 and earlier to push a

          // history entry on hash-tag change.  When replace is true, we don't

          // want this.

          if(!options.replace) this.iframe.document.open().close();

          this._updateHash(this.iframe.location, fragment, options.replace);

        }



      // If you've told us that you explicitly don't want fallback hashchange-

      // based history, then `navigate` becomes a page refresh.

      } else {

        return this.location.assign(url);

      }

      if (options.trigger) this.loadUrl(fragment);

    },



    // Update the hash location, either replacing the current entry, or adding

    // a new one to the browser history.

    // 更新hash值 包含替换当前hash 或者是增加历史到浏览器的历史记录中

    _updateHash: function(location, fragment, replace) {

      if (replace) {

        var href = location.href.replace(/(javascript:|#).*$/, '');

        location.replace(href + '#' + fragment);

      } else {

        // Some browsers require that `hash` contains a leading #.

        location.hash = '#' + fragment;

      }

    }



  });



  // Create the default Backbone.history.

  // 创建默认Backbone history对象

  Backbone.history = new History;



  // Helpers

  // -------



  // Helper function to correctly set up the prototype chain, for subclasses.

  // Similar to `goog.inherits`, but uses a hash of prototype properties and

  // class properties to be extended.

  var extend = function(protoProps, staticProps) {

    var parent = this;

    var child;



    // The constructor function for the new subclass is either defined by you

    // (the "constructor" property in your `extend` definition), or defaulted

    // by us to simply call the parent's constructor.

    if (protoProps && _.has(protoProps, 'constructor')) {

      child = protoProps.constructor;

    } else {

      child = function(){ return parent.apply(this, arguments); };

    }



    // Add static properties to the constructor function, if supplied.

    _.extend(child, parent, staticProps);



    // Set the prototype chain to inherit from `parent`, without calling

    // `parent`'s constructor function.

    var Surrogate = function(){ this.constructor = child; };

    Surrogate.prototype = parent.prototype;

    child.prototype = new Surrogate;



    // Add prototype properties (instance properties) to the subclass,

    // if supplied.

    if (protoProps) _.extend(child.prototype, protoProps);



    // Set a convenience property in case the parent's prototype is needed

    // later.

    child.__super__ = parent.prototype;



    return child;

  };



  // Set up inheritance for the model, collection, router, view and history.

  Model.extend = Collection.extend = Router.extend = View.extend = History.extend = extend;



  // Throw an error when a URL is needed, and none is supplied.

  var urlError = function() {

    throw new Error('A "url" property or function must be specified');

  };



  // Wrap an optional error callback with a fallback error event.

  var wrapError = function (model, options) {

    var error = options.error;

    options.error = function(resp) {

      if (error) error(model, resp, options);

      model.trigger('error', model, resp, options);

    };

  };



}).call(this);

欢迎指导、纠错、建议。