(function(){
  var isReady=false; //判斷onDOMReady方法是否已經(jīng)被執(zhí)行過
  var readyList= [];//把需要執(zhí)行的方法先暫存在這個數(shù)組里
  var timer;//定時器句柄
 
  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)生后清除定時器
     timer = null;
    }
   }
  };
 
  if(document.addEventListener){
   document.addEventListener("DOMContentLoaded", bindReady, false);
  }
  else if(document.attachEvent)//非最頂級父窗口
 
  {
   document.attachEvent("onreadystatechange", function(){
    if((/loaded|complete/).test(document.readyState))
    bindReady();
   });
 
  if(window == window.top)//在應(yīng)用有frameset或者iframe的頁面時，parent是父窗口，top是最頂級父窗口（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)
 //也可以通過閉包來使用
 ready(function(){
  //這里是邏輯代碼
 });