昨天在论坛上看见一个兄弟在提这个问题，就自己作了一个小例子，感觉很有意思，今天放了上来
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<script language='javascript'>
function get_scrollTop_of_body(){
var a = document.getElementById('div1');
var scrollTop;
if(typeof window.pageYOffset != 'undefined'){
scrollTop = window.pageYOffset;
}
else
if(typeof document.compatMode != 'undefined' &&
document.compatMode != 'BackCompat'){
scrollTop = document.documentElement.scrollTop;
}
else
if(typeof document.body != 'undefined'){
scrollTop = document.body.scrollTop;
}
if(scrollTop!=0)
{
a.style.display='block';
}
else
{
a.style.display='none';
}
}
</script>
</HEAD>
<BODY οnscrοll='get_scrollTop_of_body()'>
<a name="tt">
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<div id="div1" width="200" style='display:none;'><a href="#tt" target="_blank" rel="external nofollow" >回到顶部</a></div>
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<script language="javascript">
var divView = document.getElementById('div1');
alert(document.body.clientWidth-divView.offsetWidth);
divView.style.position="absolute";
divView.style.right = "10px";
divView.style.bottom = "20px";
</script>
</BODY>
</HTML>
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