js向上滚动文字问题的解决

<div id=demo style="overflow:hidden; width:128px; height:300px;">
<div id=demo1>
<br/>

我

<br/>

是

<br/>

测

<br/>

试

<br/>

一

<br/>

下
</div>
<div id=demo2></div>
</div>
<script language="javascript">
var speed=30
demo2.innerHTML=demo1.innerHTML
function Marquee(){
if(demo2.offsetTop-demo.scrollTop<=0)
demo.scrollTop=0
else{
demo.scrollTop++
}
}
var MyMar=setInterval(Marquee,speed)
demo.onmouseover=function() {clearInterval(MyMar)}
demo.onmouseout=function() {MyMar=setInterval(Marquee,speed)}
</script>