利用scrollTop 制作图片无缝滚动

<!doctype html>
<title>javascript无缝滚动 by 司徒正美</title>
<meta charset="utf-8"/>
<meta name="keywords" content="javascript无缝滚动 by 司徒正美" />
<meta name="description" content="javascript无缝滚动 by 司徒正美" />
<style type="text/css">
h1 {
font:400 16px/1 "Microsoft YaHei",KaiTi_GB2312,SimSun
}
#marquee {
height:300px;
width:200px;
overflow:hidden;
position:relative;
border:10px solid #F2F1D7;
}
#marquee img {
display:block;
}
#marquee dd {
margin:0px;
padding:0px;
}
</style>
<script type="text/javascript">
var Marquee = function(id){
try{document.execCommand("BackgroundImageCache", false, true);}catch(e){};
var container = document.getElementById(id),
original = container.getElementsByTagName("dt")[0],
clone = container.getElementsByTagName("dd")[0],
speed = arguments[1] || 10;
clone.innerHTML=original.innerHTML;
alert(clone.offsetTop)
container.scrollTop = clone.offsetTop;
var rolling = function(){
if(container.scrollTop == 0){
container.scrollTop = clone.offsetTop;
}else{
container.scrollTop--;
}
}
var timer = setInterval(rolling,speed)//设置定时器
container.onmouseover=function() {clearInterval(timer)}//鼠标移到marquee上时，清除定时器，停止滚动
container.onmouseout=function() {timer=setInterval(rolling,speed)}//鼠标移开时重设定时器
}
window.onload = function(){
Marquee("marquee");
}
</script>
<h1>javascript无缝滚动(向下滚动) by 司徒正美</h1>