异步加载js

    //异步加载js
    function loadScript(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: Firefox, Safari, Chrome, and Opera
            script.onload = function(){
            callback();
        }
        }
        script.src = url;
        document.getElementsByTagName("head")[0].appendChild(script);
    }  

【未完待续】