(function(){
 var isReady=false; //判斷onDOMReady方法是否已經(jīng)被執(zhí)行過(guò)
 var readyList= [];//把需要執(zhí)行的方法先暫存在這個(gè)數(shù)組里
 var timer;//定時(shí)器句柄
 
 ready=function(fn)
 {
 if (isReady )
 fn.call( document);
 else
 readyList.push( function() { return fn.call(this);});
 return this;
 }
 
 var onDOMReady=function(){
 for(var i=0;i< readyList.length;i++)
 {
 readyList[i].apply(document);
 }
 readyList = null;
 }
 
 var bindReady = function(evt)
 {
 if(isReady) return;
 isReady=true;
 onDOMReady.call(window);
 if(document.removeEventListener)
 {
 document.removeEventListener("DOMContentLoaded", bindReady, false);
 }
 else if(document.attachEvent)
 {
 document.detachEvent("onreadystatechange", bindReady);
 if(window == window.top){
 clearInterval(timer);//事件發(fā)生后清除定時(shí)器
 timer = null;
 }
 }
 };
 
 if(document.addEventListener){
 document.addEventListener("DOMContentLoaded", bindReady, false);
 }
 else if(document.attachEvent)//非最頂級(jí)父窗口
 
 {
 document.attachEvent("onreadystatechange", function(){
 if((/loaded|complete/).test(document.readyState))
 bindReady();
 });
 
 if(window == window.top)//在應(yīng)用有frameset或者iframe的頁(yè)面時(shí)，parent是父窗口，top是最頂級(jí)父窗口（有的窗口中套了好幾層frameset或者iframe)
 {
 timer = setInterval(function(){
 try
 {
 isReady||document.documentElement.doScroll('left');//在IE下用能否執(zhí)行doScroll判斷 dom是否加載完畢
 }
 catch(e)
 {
 return;
 }
 bindReady();
 },5);
 }
 }
 })();

 ready(dosomething);//dosomething為已存在的函數(shù)
 //也可以通過(guò)閉包來(lái)使用
 ready(function(){
 //這里是邏輯代碼
 });