loadScript.js

 function addScript(url, callback) {
        var script = docElement.createElement("script"),
            scriptLoaded = 0;

        // IE和opera支持onreadystatechange
        // safari、chrome、opera支持onload
        script.onload = script.onreadystatechange = function() {
            // 避免opera下的多次调用
            if (scriptLoaded) {
                return;
            };

            var readyState = script.readyState;
            if ('undefined' == typeof readyState || readyState == "loaded" || readyState == "complete") {
                scriptLoaded = 1;
                try {
                    callback();
                } finally {
                    script.onload = script.onreadystatechange = null;
                    script.parentNode.removeChild(script);
                }
            }
        };

        script.asyn = 1;
        script.src = url;
        var lastScript = docElement.getElementsByTagName("script")[0];
        lastScript.parentNode.insertBefore(script, lastScript);
    }