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);   };}