// Only do anything if jQuery isn‘t definedif (typeof jQuery == ‘undefined‘) {    if (typeof $ == ‘function‘) {        // warning, global var        thisPageUsingOtherJSLibrary = true;    }        function getScript(url, success) {            var script     = document.createElement(‘script‘);             script.src = url;                var head = document.getElementsByTagName(‘head‘)[0],        done = false;                // Attach handlers for all browsers        script.onload = script.onreadystatechange = function() {                    if (!done && (!this.readyState || this.readyState == ‘loaded‘ || this.readyState == ‘complete‘)) {                        done = true;                                // callback function provided as param                success();                                script.onload = script.onreadystatechange = null;                head.removeChild(script);                            };                };                head.appendChild(script);        };        getScript(‘http://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js‘, function() {            if (typeof jQuery==‘undefined‘) {                    // Super failsafe - still somehow failed...                } else {                    // jQuery loaded! Make sure to use .noConflict just in case            fancyCode();                        if (thisPageUsingOtherJSLibrary) {                // Run your jQuery Code            } else {                // Use .noConflict(), then run your jQuery Code            }                }        });    } else { // jQuery was already loaded        // Run your jQuery Code};//该代码片段来自于: http://www.sharejs.com/codes/javascript/4281

var jQueryScriptOutputted = false;function initJQuery() {        //if the jQuery object isn‘t available    if (typeof(jQuery) == ‘undefined‘) {            if (! jQueryScriptOutputted) {            //only output the script once..            jQueryScriptOutputted = true;                        //output the script (load it from google api)            document.write("<scr" + "ipt type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></scr" + "ipt>");        }        setTimeout("initJQuery()", 50);    } else {                                $(function() {              // do anything that needs to be done on document.ready            // don‘t really need this dom ready thing if used in footer        });    }            }initJQuery();//该代码片段来自于: http://www.sharejs.com/codes/javascript/4281