JavaScript实现多张Banner图片广告轮播切换

<html>
<head>
<title>图片广告交替显示</title>
<script language="JavaScript" type="text/JavaScript">
<!--
var urlArray = new Array(3); 
var banArray = new Array(3); 
var counter = 1;
var url = "https://www.jb51.net/"; //initial URL
urlArray[0] = "https://www.jb51.net/";
urlArray[1] = "http://www.baidu.com/";
urlArray[2] = "http://www.163.com/";
if(document.images) 
{
 for(i = 0; i < 3; i++)
 {
  banArray[i] = new Image(200, 60);
  banArray[i].src = "images/wall_s" + (i+1) + ".jpg";
 }
}
function changeBanner() 
{
 if(counter > 2)
  counter = 0;
 document.banner.src = banArray[counter].src; //sets a new banner
 url = urlArray[counter]; 
 counter++; 
}
var timer = window.setInterval("changeBanner()", 3000);
//-->
</script>
</head>
<body>
<a href="#" onClick="window.open(url,'BannerWin');">
<img src="images/wall_s1.jpg" width=200 height=60 border=0 
name="banner"></a>
</body>
</html>