js不间断向下滚动

<div id=demo style=overflow:hidden;height:139;width:232;background:#f4f4f4;color:#ffffff><div id=demo1><img src=" http://www.lanrentuku.com/down/js/images/12460764740.jpg"><img src=" http://www.lanrentuku.com/down/js/images/12460764741.jpg"><img src=" http://www.lanrentuku.com/down/js/images/12460764742.jpg"><img src=" http://www.lanrentuku.com/down/js/images/12460764743.jpg"><img src=" http://www.lanrentuku.com/down/js/images/12460764744.jpg"></div>
  <div id=demo2></div>
  </div>
    <script>
    var speed=30
    demo2.innerHTML=demo1.innerHTML
    demo.scrollTop=demo.scrollHeight
    function Marquee(){
    if(demo1.offsetTop-demo.scrollTop>=0)
    demo.scrollTop+=demo2.offsetHeight
    else{
    demo.scrollTop--
    }
    }
    var MyMar=setInterval(Marquee,speed)
    demo.οnmοuseοver=function() {clearInterval(MyMar)}
    demo.οnmοuseοut=function() {MyMar=setInterval(Marquee,speed)}
    </script>
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