JS跨文件控制多个iframe页面的实现方案

<!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=gb2312" /> 
<title>无标题文档</title> 
<meta http-equiv="refresh" content="3;URL=#" /> 
</head> 
<script type="text/javascript"> 
function change(){ 
var a = document.getElementById("iframea"); 
var b = document.getElementById("iframeb"); 
a.setAttribute("src","http://www.163.com"); 
b.setAttribute("src","http://www.sina.com"); 
} 
</script> 
<body> 
<!--#include file="z.html" -->  
<iframe id="iframea" src="http://www.baidu.com/" width="450" height="300"></iframe> 
<iframe id="iframeb" src="http://www.g.cn/" width="450" height="300">></iframe> 
</body> 
</html> 

<a href="#" onclick="change()">其中内容点击链接更新两个iframe</a>