動態載入javascript

/**title:動態載入script檔案*description:動態載入scrip*time：2012-05-16*/function load_script(url, callback) {    var script = document.createElement('script');    script.type = 'text/javascript';    if (script.readyState) {  //IE         script.onreadystatechange = function() {            if (script.readyState == 'loaded' || script.readyState == 'complete') {                script.onreadystatechange = null;                callback();            }        }    } else {  //others         script.onload = function() {            callback();        }    }    script.src = url;    document.getElementsByTagName('head')[0].appendChild(script);}/***動態載入js 摘自:http://www.zhangjingwei.com/archives/asynchronous-loading-js/*description:同步載入，按順序載入javascript檔案*/var loadscript ={    $$: function(id) { return document.getElementById(id) },    tag: function(element) { return document.getElementsByTagName(element) },    ce: function(element) { return document.createElement(element) },    ls: function(url) {        var req = this.createXmlHttp();        req.open('GET', url, false);        req.send(null);        try {            if (req.status == 200 || req.status == 0)                window.eval(req.responseText);        } catch (e) { }    },    createXmlHttp: function() {        var xmlHttp;        if (window.ActiveXObject) {            xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");        } else if (window.XMLHttpRequest) {            xmlHttp = new XMLHttpRequest();        }        return xmlHttp;    }}