滚动广告代码？请帮忙解释下如何运行的

Question

<div id=demo  >
                        <div id=demo1 class="demo"> </div>
                        <div id=demo2 class="demo" style="height:170px;"></div>
                      </div>
<script lang="javascript" >
   var speed=100;  document.getElementById('demo2').innerHTML=document.getElementById('demo1').innerHTML;
   function Marquee(){
   if(document.getElementById('demo2').offsetTop-document.getElementById('demo').scrollTop<=0)
  document.getElementById('demo').scrollTop-=document.getElementById('demo1').offsetHeight
   else{
   document.getElementById('demo').scrollTop++
   }
   }
   var MyMar=setInterval(Marquee,speed)
 document.getElementById('demo').onmouseover=function() {clearInterval(MyMar)}
document.getElementById('demo').onmouseout=function() {MyMar=setInterval(Marquee,speed)}
                    </script>

Answer 1

这个在Valsue Stutio 中调试就可以知道回事了，大体就是层随滚动条以100px动态滚动。