Hash.js

/*!
 * Copyright (c) 2009-2011 Andreas Blixt <andreas@blixt.org>
 * Contributors: Aaron Ogle <aogle@avencia.com>,
 *               Matti Virkkunen <mvirkkunen@gmail.com>,
 *               Simon Chester <simonches@gmail.com>
 * http://github.com/blixt/js-hash
 * MIT License: http://www.opensource.org/licenses/mit-license.php
 *
 * Hash handler
 * Keeps track of the history of changes to the hash part in the address bar.
 */
/* WARNING for Internet Explorer 7 and below:
 * If an element on the page has the same ID as the hash used, the history will
 * get messed up.
 *
 * Does not support history in Safari 2 and below.
 *
 * Example:
 *     function handler(newHash, initial) {
 *         if (initial)
 *             alert('Hash is "' + newHash + '"');
 *         else
 *             alert('Hash changed to "' + newHash + '"');
 *     }
 *     Hash.init(handler);
 *     Hash.go('abc123');
 *
 *
 * Updated by Simon Chester (simonches@gmail.com) on 2011-05-16:
 *   - Removed the need for blank.html and the iframe argument by creating the
 *     iframe on initialization.
 *
 * Updated by Matti Virkkunen (mvirkkunen@gmail.com) on 2009-11-16:
 *   - Added second argument to callback that indicates whether the callback is
 *     due to initial state (true) or due to an actual change to the hash
 *     (false).
 *
 * Updated by Aaron Ogle (aogle@avencia.com) on 2009-08-11:
 *   - Fixed bug where Firefox automatically unescapes location.hash but no
 *     other browsers do. Always get the hash by parsing location.href and
 *     never use location.hash.
 */

var Hash = (function () {
var
// Import globals
window = this,
documentMode = document.documentMode,
history = window.history,
// Plugin variables
callback, hash,
// IE-specific
iframe,

getHash = function () {
    // Internet Explorer 6 (and possibly other browsers) extracts the query
    // string out of the location.hash property into the location.search
    // property, so we can't rely on it. The location.search property can't be
    // relied on either, since if the URL contains a real query string, that's
    // what it will be set to. The only way to get the whole hash is to parse
    // it from the location.href property.
    //
    // Another thing to note is that in Internet Explorer 6 and 7 (and possibly
    // other browsers), subsequent hashes are removed from the location.href
    // (and location.hash) property if the location.search property is set.
    //
    // Via Aaron: Firefox 3.5 (and below?) always unescape location.hash which
    // causes poll to fire the hashchange event twice on escaped hashes. This
    // is because the hash variable (escaped) will not match location.hash
    // (unescaped.) The only consistent option is to rely completely on
    // location.href.
    var index = window.location.href.indexOf('#');
    return (index == -1 ? '' : window.location.href.substr(index + 1));
},

// Used by all browsers except Internet Explorer 7 and below.
poll = function () {
    var curHash = getHash();
    if (curHash != hash) {
        hash = curHash;
        callback(curHash, false);
    }
},

// From:
// http://perfectionkills.com/detecting-event-support-without-browser-sniffing/
isHashChangeSupported = function() {
    var eventName = 'onhashchange';
    var isSupported = (eventName in document.body);
    if (!isSupported) {
        document.body.setAttribute(eventName, 'return;');
        isSupported = typeof document.body[eventName] == 'function';
    }

    // documentMode logic from YUI to filter out IE8 Compat Mode (which
    // generates false positives).
    return isSupported && (document.documentMode === undefined ||
                           document.documentMode > 7);
},

createIframe = function () {
    var tempEl = document.createElement();
    tempEl.innerHTML = '<iframe src="javascript:void(0)" tabindex="-1" ' +
                       'style="display: none;"></iframe>';
    var frame = tempEl.childNodes[0];
    document.body.appendChild(frame);
    return frame;
},

// Used to create a history entry with a value in the iframe.
setIframe = function (newHash) {
    try {
        var doc = iframe.contentWindow.document;
        doc.open();
        doc.write('<html><body>' + newHash + '</body></html>');
        doc.close();
        hash = newHash;
    } catch (e) {
        setTimeout(function () { setIframe(newHash); }, 10);
    }
},

// Used by Internet Explorer 7 and below to set up an iframe that keeps track
// of history changes.
setUpIframe = function () {
    // Don't run until access to the body is allowed.
    try {
        iframe = createIframe();
    } catch (e) {
        setTimeout(setUpIframe, 10);
        return;
    }

    // Create a history entry for the initial state.
    setIframe(hash);
    var data = hash;

    setInterval(function () {
        var curData, curHash;

        try {
            curData = iframe.contentWindow.document.body.innerText;
            if (curData != data) {
                data = curData;
                window.location.hash = hash = curData;
                callback(curData, true);
            } else {
                curHash = getHash();
                if (curHash != hash) setIframe(curHash);
            }
        } catch (e) {
        }
    }, 50);
};

return {
    init: function (cb) {
        // init can only be called once.
        if (callback) return;

        callback = cb;

        // Keep track of the hash value.
        hash = getHash();
        cb(hash, true);

        if (isHashChangeSupported()) {
            if (window.addEventListener){
              window.addEventListener('hashchange', poll, false);
            } else if (window.attachEvent){
              window.attachEvent('onhashchange', poll);
            }
        } else {
            // Run specific code for Internet Explorer.
            if (window.ActiveXObject) {
                if (!documentMode || documentMode < 8) {
                    // Internet Explorer 5.5/6/7 need an iframe for history
                    // support.
                    setUpIframe();
                }
            } else {
                // Change Opera navigation mode to improve history support.
                if (history.navigationMode) {
                    history.navigationMode = 'compatible';
                }

                setInterval(poll, 50);
            }
        }
    },

    go: function (newHash) {
        // Cancel if the new hash is the same as the current one, since there
        // is no cross-browser way to keep track of navigation to the exact
        // same hash multiple times in a row. A wrapper can handle this by
        // adding an incrementing counter to the end of the hash.
        if (newHash == hash) return;
        if (iframe) {
            setIframe(newHash);
        } else {
            window.location.hash = hash = newHash;
            callback(newHash, false);
        }
    },
    
    getHash: getHash
};
})();