确保页面中JS加载完全

var n = document.createElement("script");

n.type = "text/javascript";

//以上省略部分代码

//ie支持script的readystatechange属性

if(ua.ie){

   n.onreadystatechange = function(){

       var rs = this.readyState;

       if('loaded' === rs || 'complete'===rs){

           n.onreadystatechange = null;

           f(id,url); //回调函数

       }

};

//省略部分代码

//safari 3.x supports the load event for script nodes(DOM2)

   n.addEventListener('load',function(){

       f(id,url);

   });

//firefox and opera support onload(but not dom2 in ff) handlers for

//script nodes. opera, but no ff, support the onload event for link

//nodes.

}else{

   n.onload = function(){

       f(id,url);

   };

}