backbone.js1.3.3------------------history和router

backbone的router和history对象就是对window.history对象的操作。

学习backbone的router和history之前必须要学习window.history对象。html5给开发者添加了操作history的api。

这里需要了解两个概念：

hash：个人理解，hash就是url最后#后面的东西，可以定位到页面的某一个位置

state：是指push到window.history中的对象。

history可以在不刷新页面的情况下修改url地址，这里就使用了锚点。通过向history中添加锚点不同的url，这样就可以做到通过浏览器的前进后退修改url而不刷新页面（其实只是监听事件后跳转到锚点所在的位置）。

在ajax给我们带来提高用户体验，减少http请求好处的同时，显露出了一些不足：

1.无法使用浏览器的前进后退按钮。

2.直接复制浏览器url，在新窗口中打开时不是我们想要的页面。

3.单纯的使用ajax不利于搜索引擎优化，因为搜索引擎无法获取ajax请求的内容

可以利用history解决这个问题。

// Backbone.Router
  // ---------------

  // Routers map faux-URLs to actions, and fire events when routes are
  // matched. Creating a new one sets its `routes` hash, if not set statically.
  var Router = Backbone.Router = function(options) {
    options || (options = {});
    this.preinitialize.apply(this, arguments);
    if (options.routes) this.routes = options.routes;
    this._bindRoutes();
    this.initialize.apply(this, arguments);
  };

  // Cached regular expressions for matching named param parts and splatted
  // parts of route strings.
  var optionalParam = /((.*?))/g;
  var namedParam    = /((?)?:w+/g;
  var splatParam    = /*w+/g;
  var escapeRegExp  = /[-{}[]+?.,\^$|#s]/g;

  // Set up all inheritable **Backbone.Router** properties and methods.
  _.extend(Router.prototype, Events, {

    // preinitialize is an empty function by default. You can override it with a function
    // or object.  preinitialize will run before any instantiation logic is run in the Router.
    preinitialize: function(){},

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize: function(){},

    // Manually bind a single named route to a callback. For example:
    //
    //     this.route('search/:query/p:num', 'search', function(query, num) {
    //       ...
    //     });
    //
    //这里调用了backbone.history.route方法将这个对象添加到了backbone.history的handlers中，这样可在backbone.history的loadurl方法遍历handlers并执行匹配的url
    route: function(route, name, callback) {
      if (!_.isRegExp(route)) route = this._routeToRegExp(route);
      if (_.isFunction(name)) {
        callback = name;
        name = '';
      }
      if (!callback) callback = this[name];
      var router = this;
      Backbone.history.route(route, function(fragment) {
        var args = router._extractParameters(route, fragment);
        if (router.execute(callback, args, name) !== false) {
          router.trigger.apply(router, ['route:' + name].concat(args));
          router.trigger('route', name, args);
          Backbone.history.trigger('route', router, name, args);
        }
      });
      return this;
    },

    // Execute a route handler with the provided parameters.  This is an
    // excellent place to do pre-route setup or post-route cleanup.
    execute: function(callback, args, name) {
      if (callback) callback.apply(this, args);
    },

    // Simple proxy to `Backbone.history` to save a fragment into the history.
    navigate: function(fragment, options) {
      Backbone.history.navigate(fragment, options);
      return this;
    },

    // Bind all defined routes to `Backbone.history`. We have to reverse the
    // order of the routes here to support behavior where the most general
    // routes can be defined at the bottom of the route map.
    _bindRoutes: function() {
      if (!this.routes) return;
      this.routes = _.result(this, 'routes');
      var route, routes = _.keys(this.routes);
      while ((route = routes.pop()) != null) {
        this.route(route, this.routes[route]);
      }
    },

    // Convert a route string into a regular expression, suitable for matching
    // against the current location hash.
    _routeToRegExp: function(route) {
      route = route.replace(escapeRegExp, '\$&')
                   .replace(optionalParam, '(?:$1)?')
                   .replace(namedParam, function(match, optional) {
                     return optional ? match : '([^/?]+)';
                   })
                   .replace(splatParam, '([^?]*?)');
      return new RegExp('^' + route + '(?:\?([\s\S]*))?$');
    },

    // Given a route, and a URL fragment that it matches, return the array of
    // extracted decoded parameters. Empty or unmatched parameters will be
    // treated as `null` to normalize cross-browser behavior.
    _extractParameters: function(route, fragment) {
      var params = route.exec(fragment).slice(1);
      return _.map(params, function(param, i) {
        // Don't decode the search params.
        if (i === params.length - 1) return param || null;
        return param ? decodeURIComponent(param) : null;
      });
    }

  });

  // Backbone.History
  // ----------------

  // Handles cross-browser history management, based on either
  // [pushState](http://diveintohtml5.info/history.html) and real URLs, or
  // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)
  // and URL fragments. If the browser supports neither (old IE, natch),
  // falls back to polling.
  var History = Backbone.History = function() {
    this.handlers = [];
    this.checkUrl = _.bind(this.checkUrl, this);

    // Ensure that `History` can be used outside of the browser.
    if (typeof window !== 'undefined') {
      this.location = window.location;
      this.history = window.history;
    }
  };

  // Cached regex for stripping a leading hash/slash and trailing space.
  var routeStripper = /^[#/]|s+$/g;

  // Cached regex for stripping leading and trailing slashes.
  var rootStripper = /^/+|/+$/g;

  // Cached regex for stripping urls of hash.
  var pathStripper = /#.*$/;

  // Has the history handling already been started?
  History.started = false;

  // Set up all inheritable **Backbone.History** properties and methods.
  _.extend(History.prototype, Events, {

    // The default interval to poll for hash changes, if necessary, is
    // twenty times a second.
    interval: 50,

    // Are we at the app root?
    atRoot: function() {
      var path = this.location.pathname.replace(/[^/]$/, '$&/');
      return path === this.root && !this.getSearch();
    },

    // Does the pathname match the root?
    matchRoot: function() {
      var path = this.decodeFragment(this.location.pathname);
      var rootPath = path.slice(0, this.root.length - 1) + '/';
      return rootPath === this.root;
    },

    // Unicode characters in `location.pathname` are percent encoded so they're
    // decoded for comparison. `%25` should not be decoded since it may be part
    // of an encoded parameter.
    decodeFragment: function(fragment) {
      return decodeURI(fragment.replace(/%25/g, '%2525'));
    },

    // In IE6, the hash fragment and search params are incorrect if the
    // fragment contains `?`.
    getSearch: function() {
      var match = this.location.href.replace(/#.*/, '').match(/?.+/);
      return match ? match[0] : '';
    },

    // Gets the true hash value. Cannot use location.hash directly due to bug
    // in Firefox where location.hash will always be decoded.
    getHash: function(window) {
      var match = (window || this).location.href.match(/#(.*)$/);
      return match ? match[1] : '';
    },

    // Get the pathname and search params, without the root.
    getPath: function() {
      var path = this.decodeFragment(
        this.location.pathname + this.getSearch()
      ).slice(this.root.length - 1);
      return path.charAt(0) === '/' ? path.slice(1) : path;
    },

    // Get the cross-browser normalized URL fragment from the path or hash.
    getFragment: function(fragment) {
      if (fragment == null) {
        if (this._usePushState || !this._wantsHashChange) {
          fragment = this.getPath();
        } else {
          fragment = this.getHash();
        }
      }
      return fragment.replace(routeStripper, '');
    },

    // Start the hash change handling, returning `true` if the current URL matches
    // an existing route, and `false` otherwise.
    //完成以下事情：
    //options={root:'',
    //hashChange:''默认为true,
    //pushState:''默认为true}
    //1.解析option初始化参数。
    //2.监听popstate和hashchange事件触发则执行checkurl。若不支持，则定时执行checkurl
    start: function(options) {
      if (History.started) throw new Error('Backbone.history has already been started');
      History.started = true;
      // Figure out the initial configuration. Do we need an iframe?
      // Is pushState desired ... is it available?
      this.options          = _.extend({root: '/'}, this.options, options);
      this.root             = this.options.root;
      this._wantsHashChange = this.options.hashChange !== false;
      this._hasHashChange   = 'onhashchange' in window && (document.documentMode === void 0 || document.documentMode > 7);
      this._useHashChange   = this._wantsHashChange && this._hasHashChange;
      this._wantsPushState  = !!this.options.pushState;
      this._hasPushState    = !!(this.history && this.history.pushState);
      this._usePushState    = this._wantsPushState && this._hasPushState;
      this.fragment         = this.getFragment();

      // Normalize root to always include a leading and trailing slash.
      this.root = ('/' + this.root + '/').replace(rootStripper, '/');

      // Transition from hashChange to pushState or vice versa if both are
      // requested.
      if (this._wantsHashChange && this._wantsPushState) {

        // If we've started off with a route from a `pushState`-enabled
        // browser, but we're currently in a browser that doesn't support it...
        if (!this._hasPushState && !this.atRoot()) {
          var rootPath = this.root.slice(0, -1) || '/';
          this.location.replace(rootPath + '#' + this.getPath());
          // Return immediately as browser will do redirect to new url
          return true;

        // Or if we've started out with a hash-based route, but we're currently
        // in a browser where it could be `pushState`-based instead...
        } else if (this._hasPushState && this.atRoot()) {
          this.navigate(this.getHash(), {replace: true});
        }

      }

      // Proxy an iframe to handle location events if the browser doesn't
      // support the `hashchange` event, HTML5 history, or the user wants
      // `hashChange` but not `pushState`.
      if (!this._hasHashChange && this._wantsHashChange && !this._usePushState) {
        this.iframe = document.createElement('iframe');
        this.iframe.src = 'javascript:0';
        this.iframe.style.display = 'none';
        this.iframe.tabIndex = -1;
        var body = document.body;
        // Using `appendChild` will throw on IE < 9 if the document is not ready.
        var iWindow = body.insertBefore(this.iframe, body.firstChild).contentWindow;
        iWindow.document.open();
        iWindow.document.close();
        iWindow.location.hash = '#' + this.fragment;
      }

      // Add a cross-platform `addEventListener` shim for older browsers.
      var addEventListener = window.addEventListener || function(eventName, listener) {
        return attachEvent('on' + eventName, listener);
      };

      // Depending on whether we're using pushState or hashes, and whether
      // 'onhashchange' is supported, determine how we check the URL state.
      if (this._usePushState) {
        addEventListener('popstate', this.checkUrl, false);
      } else if (this._useHashChange && !this.iframe) {
        addEventListener('hashchange', this.checkUrl, false);
      } else if (this._wantsHashChange) {
        this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
      }

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

    // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
    // but possibly useful for unit testing Routers.
    stop: function() {
      // Add a cross-platform `removeEventListener` shim for older browsers.
      var removeEventListener = window.removeEventListener || function(eventName, listener) {
        return detachEvent('on' + eventName, listener);
      };

      // Remove window listeners.
      if (this._usePushState) {
        removeEventListener('popstate', this.checkUrl, false);
      } else if (this._useHashChange && !this.iframe) {
        removeEventListener('hashchange', this.checkUrl, false);
      }

      // Clean up the iframe if necessary.
      if (this.iframe) {
        document.body.removeChild(this.iframe);
        this.iframe = null;
      }

      // Some environments will throw when clearing an undefined interval.
      if (this._checkUrlInterval) clearInterval(this._checkUrlInterval);
      History.started = false;
    },

    // Add a route to be tested when the fragment changes. Routes added later
    // may override previous routes.
    route: function(route, callback) {
      this.handlers.unshift({route: route, callback: callback});
    },

    // Checks the current URL to see if it has changed, and if it has,
    // calls `loadUrl`, normalizing across the hidden iframe.
    //最终会执行loadURL
    checkUrl: function(e) {
      var current = this.getFragment();

      // If the user pressed the back button, the iframe's hash will have
      // changed and we should use that for comparison.
      if (current === this.fragment && this.iframe) {
        current = this.getHash(this.iframe.contentWindow);
      }

      if (current === this.fragment) return false;
      if (this.iframe) this.navigate(current);
      this.loadUrl();
    },

    // Attempt to load the current URL fragment. If a route succeeds with a
    // match, returns `true`. If no defined routes matches the fragment,
    // returns `false`.
    //在router中寻找
    loadUrl: function(fragment) {
      // If the root doesn't match, no routes can match either.
      if (!this.matchRoot()) return false;
      fragment = this.fragment = this.getFragment(fragment);
      return _.some(this.handlers, function(handler) {
        if (handler.route.test(fragment)) {
          handler.callback(fragment);
          return true;
        }
      });
    },

    // Save a fragment into the hash history, or replace the URL state if the
    // 'replace' option is passed. You are responsible for properly URL-encoding
    // the fragment in advance.
    //
    // The options object can contain `trigger: true` if you wish to have the
    // route callback be fired (not usually desirable), or `replace: true`, if
    // you wish to modify the current URL without adding an entry to the history.
    navigate: function(fragment, options) {
      if (!History.started) return false;
      if (!options || options === true) options = {trigger: !!options};

      // Normalize the fragment.
      fragment = this.getFragment(fragment || '');

      // Don't include a trailing slash on the root.
      var rootPath = this.root;
      if (fragment === '' || fragment.charAt(0) === '?') {
        rootPath = rootPath.slice(0, -1) || '/';
      }
      var url = rootPath + fragment;

      // Strip the fragment of the query and hash for matching.
      fragment = fragment.replace(pathStripper, '');

      // Decode for matching.
      var decodedFragment = this.decodeFragment(fragment);

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

      // If pushState is available, we use it to set the fragment as a real URL.
      if (this._usePushState) {
        this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);

      // If hash changes haven't been explicitly disabled, update the hash
      // fragment to store history.
      } else if (this._wantsHashChange) {
        this._updateHash(this.location, fragment, options.replace);
        if (this.iframe && fragment !== this.getHash(this.iframe.contentWindow)) {
          var iWindow = this.iframe.contentWindow;

          // Opening and closing the iframe tricks IE7 and earlier to push a
          // history entry on hash-tag change.  When replace is true, we don't
          // want this.
          if (!options.replace) {
            iWindow.document.open();
            iWindow.document.close();
          }

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

      // If you've told us that you explicitly don't want fallback hashchange-
      // based history, then `navigate` becomes a page refresh.
      } else {
        return this.location.assign(url);
      }
      if (options.trigger) return this.loadUrl(fragment);
    },

    // Update the hash location, either replacing the current entry, or adding
    // a new one to the browser history.
    _updateHash: function(location, fragment, replace) {
      if (replace) {
        var href = location.href.replace(/(javascript:|#).*$/, '');
        location.replace(href + '#' + fragment);
      } else {
        // Some browsers require that `hash` contains a leading #.
        location.hash = '#' + fragment;
      }
    }

  });

  // Create the default Backbone.history.
  Backbone.history = new History;