有些时候我们需要动态的加载一些JS，并在JS加载完成后执行一些回调函数。

var loadscript = {    $$: function (id) {        return document.getElementById(id);    },    tag: function (element) {        return document.getElementsByTagName(element);    },    ce: function (element) {        return document.createElement(element);    },    js: function (url, callback) {        var s = loadscript.ce('script');        s.type = "text/javascript";        s.src = url;        if (document.documentMode == 10 || document.documentMode == 9) {            s.onerror = s.onload = loaded;        } else {            s.onreadystatechange = ready;            s.onerror = s.onload = loaded;        }        loadscript.tag('head')[0].appendChild(s);        function ready() { /*IE7.0/IE10.0*/            if (s.readyState == 'loaded' || s.readyState == 'complete') {                callback();            }        }        function loaded() { /*chrome/IE10.0*/            callback();        }    }};//加载百度的uaredirect.js，回调执行uaredirect函数loadscript.js("http://siteapp.baidu.com/static/webappservice/uaredirect.js", function() {    uaredirect("https://m.baidu.com/");});

参考网址：

http://www.cnblogs.com/jyk/archive/2013/05/14/3078024.htmlhttp://www.cnblogs.com/w-y-f/p/3469211.htmlhttp://www.xiariboke.com/design/2857.html