JavaScript 实现文字无缝上下滚动效果

<!DOCTYPE html>
<html>
<head>
 <meta charset="utf-8">
 <meta name="author" content="" />
 <title>文字列表无缝滚动代码</title>
 <style type="text/css">
  *{
   margin:0px;
   padding:0px;
   border:0px;
  }
  body{font-size:12px}
  #demo{
   overflow:hidden;
   height:80px;
   width:280px;
   margin:90px auto;
   position:relative;
  }
  #demo1{
   height:auto;
   text-align:left;
  }
  #demo2{
   height:auto;
   text-align:left;
  }
  #demo1 li{
   list-style-type:none;
   height:22px;
   text-align:left;
   text-indent:15px;
  }
  #demo2 li{
   list-style-type:none;
   height:22px;
   text-align:left;
   text-indent:15px;
  }
 </style>
</head>
<body>
<div id="demo">
 <ul id="demo1">
  <li>1</li>
  <li>2</li>
  <li>3</li>
  <li>4</li>
  <li>5</li>
  <li>6</li>
  <li>7</li>
 </ul>
 <div id="demo2"></div>
</div>
<script type="text/javascript">
 var speed=40
  // 向上滚动
  var demo=document.getElementById("demo");
  var demo2=document.getElementById("demo2");
  var demo1=document.getElementById("demo1");
  demo2.innerHTML=demo1.innerHTML
  function Marquee(){
   if(demo.scrollTop>=demo1.offsetHeight){
    demo.scrollTop=0;
   }
   else{
    demo.scrollTop=demo.scrollTop+1;
   }
  }
  var MyMar=setInterval(Marquee,speed)
  demo.onmouseover=function(){clearInterval(MyMar)}
  demo.onmouseout=function(){MyMar=setInterval(Marquee,speed)}
 //向下滚动
 // demo2.innerHTML=demo1.innerHTML
 // demo.scrollTop=demo.scrollHeight
 // function Marquee2(){
 //  if(demo1.offsetTop-demo.scrollTop>=0)
 //   demo.scrollTop+=demo2.offsetHeight
 //  else{
 //   demo.scrollTop--
 //  }
 // }
 // var MyMar2=setInterval(Marquee2,speed)
 // demo.onmouseover=function() {clearInterval(MyMar2)}
 // demo.onmouseout=function() {MyMar2=setInterval(Marquee2,speed)}
</script>
</body>
</html>