(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);
    timer = null;
   }
  }
 };
 if(document.addEventListener){
  document.addEventListener("DOMContentLoaded", bindReady, false);
 }
 else if(document.attachEvent)
 {
  document.attachEvent("onreadystatechange", function(){
   if((/loaded|complete/).test(document.readyState))
   bindReady();
  });
 if(window == window.top)
 {
  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
});