一个小小的script问题。 - 黑马程序员技术交流社区

<!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">
<script type="text/javascript">
function $(id)
{
return document.getElementById(id);
}
window.onload = function()
{
var demo1 = $("demo1");
var demo2 = $("demo2");
demo2.innerHTML = demo1.innerHTML;
alert($("demo2").offsetHeight);
window.setInterval(textscroll,50);
}
function textscroll()
{
var demo = $("demo");
if(demo.scrollTop-$("demo2").offsetHeight>=0) //问题一：怎么判断出滚动条出来的部分就是demo2的总高？
{
demo.scrollTop = 0;
}else
{
demo.scrollTop++;
}
}
</script>
<style>
*{ margin:0px; padding:0px}
ul{ list-style:none}
#demo{ border:#999 solid ; text-align:center; background:#930;width:150px; height:160px; overflow:hidden; margin:auto}
</style>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<body>
<div id="demo">
<div id="demo1">
<ul>
<li>11111111</li>
<li>22222222</li>
<li>33333333</li>
<li>44444444</li>
<li>55555555</li>
<li>66666666</li>
<li>77777777</li>
<li>88888888</li>
<li>99999999</li>
<li>00000000</li>
</ul>
</div>
<div id="demo2"></div>
</div>
</body>
</html>

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