javascript完美随机广告代码

<script language=javascript>
var m=5; //共几个Banner随机显示
var n=Math.floor(Math.random()*m+1)
switch(n)
{
case 1:
document.write('Banner1的HTML');
break;
case 2:
document.write('Banner2的HTML');
break;
case 3:
document.write('Banner3的HTML');
break;
case 4:
document.write('Banner4的HTML');
break;
case 5:
document.write('Banner5的HTML');
break;
}
</script>