无缝滚动有关问题 _JavaScript

无缝滚动问题
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style type="text/css">
#dome{
overflow:hidden; /*溢出的部分不显示*/
height:180px;
padding:5px;
}
</style>
<script type="text/javascript">
function $(element){
return document.getElementById(element);
}
var dome=document.getElementById("dome");
var dome1=document.getElementById("dome1");
var dome2=document.getElementById("a2");
var speed=50; //设置向上滚动速度
dome2.innerHTML=dome1.innerHtml;

function moveTop(){
if(dome2.offsetTop-dome.scrollTop<=0) //当滚动至dome1与dome2交界时
dome.scrollTop-=dome1.offsetHeight //dome跳到最顶端
else{
dome.scrollTop++
}
}
var MyMar=setInterval(moveTop,speed) //设置定时器
dome.onmouseover=function() {clearInterval(MyMar)} //鼠标移上时清除定时器达到滚动停止的目的
dome.onmouseout=function() {MyMar=setInterval(moveTop,speed)} //鼠标移开时重设定时器，继续滚动

</script>
</head>

<body>
<div class="domes">

<div id="dome">
<div id="dome1">
<ul class="l">
<a href="#" onclick="mi()"><li>朋友的含义《一个像夏天一个像秋天》</li></a>
<a href="#" onclick="mi()"><li>朋友的含义《一个像夏天一个像秋天》</li></a>
<a href="#" onclick="mi()"><li>朋友的含义《一个像夏天一个像秋天》</li></a>
<a href="#" onclick="mi()"><li>朋友的含义《一个像夏天一个像秋天》</li></a>
<a href="#" onclick="mi()"><li>朋友的含义《一个像夏天一个像秋天》</li></a>
</ul>
</div>
<div id="a2"></div>
</div>
</div>

</body>
</html>

网页错误详细信息

用户代理: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.2)
时间戳: Wed, 29 Feb 2012 10:27:17 UTC

消息: 'dome2' 为空或不是对象
行: 21
字符: 1
代码: 0
URI: file:///C:/Users/du/Desktop/Untitled-1.html

------解决方案--------------------

HTML code

<%@ page language="java" pageEncoding="UTF-8"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>

<script type="text/javascript">
function opp(){
    var dome=document.getElementById("dome");
    var dome1 = document.getElementById("dome1");
    var t_ul = document.getElementById("plc").innerText;
    var dome2=document.getElementById("a2");
    var speed=50; //设置向上滚动速度
    dome2.innerHTML=dome1.innerHTML;
    
    function moveTop(){
    if(dome2.offsetTop-dome.scrollTop<=0) //当滚动至dome1与dome2交界时
    dome.scrollTop-=dome1.offsetHeight //dome跳到最顶端
    else{
    dome.scrollTop++
    }
    }
    var MyMar=setInterval(moveTop,speed) //设置定时器
    dome.onmouseover=function() {clearInterval(MyMar)} //鼠标移上时清除定时器达到滚动停止的目的
    dome.onmouseout=function() {MyMar=setInterval(moveTop,speed)} //鼠标移开时重设定时器，继续滚动
}
</script>
</head>

<body onload="opp()"> 

<div class="domes">
<div id="dome">
    <div id="dome1">
        <ul id="plc">
            <li><a href="#" onclick="mi()">朋友的含义《一个像夏天一个像秋天》</a></li>
            <li><a href="#" onclick="mi()">朋友的含义《一个像夏天一个像秋天》</a></li>
            <li><a href="#" onclick="mi()">朋友的含义《一个像夏天一个像秋天》</a></li>
            <li><a href="#" onclick="mi()">朋友的含义《一个像夏天一个像秋天》</a></li>
            <li><a href="#" onclick="mi()">朋友的含义《一个像夏天一个像秋天》</a></li>
          </ul>
    </div>
    <div id="a2"></div>

</div>
</div>

</body>
</html>