var speed=30 
demo2.innerHTML=demo1.innerHTML //克隆demo1为demo2 
function Marquee(){ 
//当滚动至demo1与demo2交界时 
if(demo2.offsetTop-demo.scrollTop<=0)   
demo.scrollTop-=demo1.offsetHeight //demo跳到最顶端 
else{ 
demo.scrollTop++ 
} 
} 
var MyMar=setInterval(Marquee,speed)//设置定时器 
//鼠标移上时清除定时器达到滚动停止的目的 
demo.onmouseover=function() {clearInterval(MyMar)} 
//鼠标移开时重设定时器 
demo.onmouseout=function(){MyMar=setInterval(Marquee,speed)}