js 无缝滚屏

<div id=demo style=overflow:auto;height:180;width:200;background:#009900;color:#006600>    <table  align=top>        <tr>            <td id=demo1 valign=top>                <p>aaaaaaaaaaa</p>                <p>aaaaaaaaaaa</p>                <p>aaaaaaaaaaa</p>                <p>aaaaaaaaaaa</p>                <p>aaaaaaaaaaa</p>                <p>aaaaaaaaaaa</p>            </td>        </tr>        <tr>            <td id=demo2 valign=top></td>        </tr>    </table></div><script>    var speed=15    demo2.innerHTML=demo1.innerHTML//克隆demo1为demo2    function Marquee(){//        console.log(demo2.offsetHeight-demo.scrollTop);        if(demo2.offsetHeight-demo.scrollTop<=0)//当滚动至demo1与demo2交界时            demo.scrollTop-=demo1.offsetHeight//demo跳到最顶端        else{            demo.scrollTop++  //如果是横向的 将 所有的 height top 改成 width left        }    }    var MyMar=setInterval(Marquee,speed)//设置定时器    demo.onmouseover=function() {clearInterval(MyMar)}//鼠标移上时清除定时器达到滚动停止的目的    demo.onmouseout=function() {MyMar=setInterval(Marquee,speed)}//鼠标移开时重设定时器</script>