backbone 学习之history

Backbone中的历史管理对象，包含兼容性的处理hash方式更改地址或者是popstate式的更改地址方案。直接看源码：

// 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;

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