js单条新闻向上滚动

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title></title>
<style>
a{display:block;font-size:15px;line-height:18px;text-decoration:none;color:#333;font-family:Arial;font-size:12px;}
.shell{
background:url(/jzxy/UploadFiles_333/201103/20110320105333511.gif) no-repeat 4px 5px;
border:1px solid #aaa;
width:400px;
padding:3px 2px 2px 20px;
}
#div1{
height:18px;
overflow:hidden;
}
</style>
</head>
<body>
<div class="shell">
<div id="div1">
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</div>
</div>
</body>
<script>
var box=document.getElementById("div1"),can=true;
box.innerHTML+=box.innerHTML;
box.onmouseover=function(){can=false};
box.onmouseout=function(){can=true};
new function (){
var stop=box.scrollTop%18==0&&!can;
if(!stop)box.scrollTop==parseInt(box.scrollHeight/2)?box.scrollTop=0:box.scrollTop++;
setTimeout(arguments.callee,box.scrollTop%18?10:1500);
};
</script>
</html>