js 页面左右两侧居中广告代码

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<title>无标题文档</title> 
<style> 
#left{ width:200px;height:450px; position:absolute; left:0px; background:red; border:1px #000 solid} 
#right{width:200px;height:450px; position:absolute; right:0px; background:blue; border:1px #000 solid} 
#x,#y{ width:10px; height:10px;position:absolute;right:0px; top:0px;} 
</style> 
<script> 
window.onload=window.onscroll=function() 
{ 
var oLeft = document.getElementById("left"); 
var oRight = document.getElementById("right"); 
var scrollY=document.documentElement.scrollTop||document.body.scrollTop; 
var clientH = document.documentElement.clientHeight; 
var oCloseX =document.getElementById("x") 
var oCloseY =document.getElementById("y") 
oLeft.style.top=(clientH-oLeft.offsetHeight)/2+scrollY+"px"; 
oRight.style.top=(clientH-oRight.offsetHeight)/2+scrollY+"px"; 
oCloseX.onclick=function() 
{ 
this.parentNode.parentNode.removeChild(this.parentNode); 
} 
} 
</script> 
</head> 
<body style="height:2000px;"> 
 
x 
 
 
x 
 
</body> 
</html>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]