# Yahoo! UI Library

### history 3.3.0

Yahoo! UI Library > history > history-html5.js (source view)
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    /**
     * Provides browser history management using the HTML5 history API.
     *
     * @module history
     * @submodule history-html5
     * @since 3.2.0
     */

    /**
     * <p>
     * Provides browser history management using the HTML5 history API.
     * </p>
     *
     * <p>
     * When calling the <code>add()</code>, <code>addValue()</code>,
     * <code>replace()</code>, or <code>replaceValue()</code> methods on
     * <code>HistoryHTML5</code>, the following additional options are supported:
     * </p>
     *
     * <dl>
     *   <dt><strong>title (String)</strong></dt>
     *   <dd>
     *     Title to use for the new history entry. Browsers will typically display
     *     this title to the user in the detailed history window or in a dropdown
     *     menu attached to the back/forward buttons. If not specified, the title
     *     of the current document will be used.
     *   </dd>
     *
     *   <dt><strong>url (String)</strong></dt>
     *   <dd>
     *     URL to display to the user for the new history entry. This URL will be
     *     visible in the browser's address bar and will be the bookmarked URL if
     *     the user bookmarks the page. It may be a relative path ("foo/bar"), an
     *     absolute path ("/foo/bar"), or a full URL ("http://example.com/foo/bar").
     *     If you specify a full URL, the origin <i>must</i> be the same as the
     *     origin of the current page, or an error will occur. If no URL is
     *     specified, the current URL will not be changed.
     *   </dd>
     * </dl>
     *
     * @class HistoryHTML5
     * @extends HistoryBase
     * @constructor
     * @param {Object} config (optional) Configuration object. The following
     *   <code>HistoryHTML5</code>-specific properties are supported in addition to
     *   those supported by <code>HistoryBase</code>:
     *
     * <dl>
     *   <dt><strong>enableSessionFallback (Boolean)</strong></dt>
     *   <dd>
     *     <p>
     *     Set this to <code>true</code> to store the most recent history state in
     *     sessionStorage in order to seamlessly restore the previous state (if any)
     *     when <code>HistoryHTML5</code> is instantiated after a
     *     <code>window.onpopstate</code> event has already fired.
     *     </p>
     *
     *     <p>
     *     By default, this setting is <code>false</code>.
     *     </p>
     *   </dd>
     * </dl>
     */

    var HistoryBase     = Y.HistoryBase,
        doc             = Y.config.doc,
        win             = Y.config.win,
        sessionStorage,
        useHistoryHTML5 = Y.config.useHistoryHTML5,

        JSON = Y.JSON || win.JSON, // prefer YUI JSON, but fall back to native

        ENABLE_FALLBACK = 'enableSessionFallback',
        SESSION_KEY     = 'YUI_HistoryHTML5_state',
        SRC_POPSTATE    = 'popstate',
        SRC_REPLACE     = HistoryBase.SRC_REPLACE;

    function HistoryHTML5() {
        HistoryHTML5.superclass.constructor.apply(this, arguments);
    }

    Y.extend(HistoryHTML5, HistoryBase, {
        // -- Initialization -------------------------------------------------------
        _init: function (config) {
            Y.on('popstate', this._onPopState, win, this);

            HistoryHTML5.superclass._init.apply(this, arguments);

            // If window.onload has already fired and the sessionStorage fallback is
            // enabled, try to restore the last state from sessionStorage. This
            // works around a shortcoming of the HTML5 history API: it's impossible
            // to get the current state if the popstate event fires before you've
            // subscribed to it. Since popstate fires immediately after onload,
            // the last state may be lost if you return to a page from another page.
            if (config && config[ENABLE_FALLBACK] && YUI.Env.windowLoaded) {
                // Gecko will throw an error if you attempt to reference
                // sessionStorage on a page served from a file:// URL, so we have to
                // be careful here.
                //
                // See http://yuilibrary.com/projects/yui3/ticket/2529165
                try {
                    sessionStorage = win.sessionStorage;
                } catch (ex) {}

                this._loadSessionState();
            }
        },

        // -- Protected Methods ----------------------------------------------------

        /**
         * Returns a string unique to the current URL pathname that's suitable for
         * use as a session storage key.
         *
         * @method _getSessionKey
         * @return {String}
         * @protected
         */
        _getSessionKey: function () {
            return SESSION_KEY + '_' + win.location.pathname;
        },

        /**
         * Attempts to load a state entry stored in session storage.
         *
         * @method _loadSessionState
         * @protected
         */
        _loadSessionState: function () {
            var lastState = JSON && sessionStorage &&
                    sessionStorage[this._getSessionKey()];

            if (lastState) {
                try {
                    this._resolveChanges(SRC_POPSTATE, JSON.parse(lastState) || null);
                } catch (ex) {}
            }
        },

        /**
         * Stores the specified state entry in session storage if the
         * <code>enableSessionFallback</code> config property is <code>true</code>
         * and either <code>Y.JSON</code> or native JSON support is available and
         * session storage is supported.
         *
         * @method _storeSessionState
         * @param {mixed} state State to store. May be any type serializable to
         *   JSON.
         * @protected
         */
        _storeSessionState: function (state) {
            if (this._config[ENABLE_FALLBACK] && JSON && sessionStorage) {
                sessionStorage[this._getSessionKey()] = JSON.stringify(state || null);
            }
        },

        /**
         * Overrides HistoryBase's <code>_storeState()</code> and pushes or replaces
         * a history entry using the HTML5 history API when necessary.
         *
         * @method _storeState
         * @param {String} src Source of the changes.
         * @param {Object} newState New state to store.
         * @param {Object} options Zero or more options.
         * @protected
         */
        _storeState: function (src, newState, options) {
            if (src !== SRC_POPSTATE) {
                win.history[src === SRC_REPLACE ? 'replaceState' : 'pushState'](
                    newState, options.title || doc.title || '', options.url || null
                );
            }

            this._storeSessionState(newState);
            HistoryHTML5.superclass._storeState.apply(this, arguments);
        },

        // -- Protected Event Handlers ---------------------------------------------

        /**
         * Handler for popstate events.
         *
         * @method _onPopState
         * @param {Event} e
         * @protected
         */
        _onPopState: function (e) {
            var state = e._event.state;

            this._storeSessionState(state);
            this._resolveChanges(SRC_POPSTATE, state || null);
        }
    }, {
        // -- Public Static Properties ---------------------------------------------
        NAME: 'historyhtml5',

        /**
         * Constant used to identify state changes originating from
         * <code>popstate</code> events.
         *
         * @property SRC_POPSTATE
         * @type String
         * @static
         * @final
         */
        SRC_POPSTATE: SRC_POPSTATE
    });

    if (!Y.Node.DOM_EVENTS.popstate) {
        Y.Node.DOM_EVENTS.popstate = 1;
    }

    Y.HistoryHTML5 = HistoryHTML5;

    /**
     * <p>
     * If <code>true</code>, the <code>Y.History</code> alias will always point to
     * <code>Y.HistoryHTML5</code> when the history-html5 module is loaded, even if
     * the current browser doesn't support HTML5 history.
     * </p>
     *
     * <p>
     * If <code>false</code>, the <code>Y.History</code> alias will always point to
     * <code>Y.HistoryHash</code> when the history-hash module is loaded, even if
     * the current browser supports HTML5 history.
     * </p>
     *
     * <p>
     * If neither <code>true</code> nor <code>false</code>, the
     * <code>Y.History</code> alias will point to the best available history adapter
     * that the browser supports. This is the default behavior.
     * </p>
     *
     * @property useHistoryHTML5
     * @type boolean
     * @for config
     * @since 3.2.0
     */

    // HistoryHTML5 will always win over HistoryHash unless useHistoryHTML5 is false
    // or HTML5 history is not supported.
    if (useHistoryHTML5 === true || (useHistoryHTML5 !== false &&
            HistoryBase.html5)) {
        Y.History = HistoryHTML5;
    }

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