为窗口添加滚动条事件其实非常的简单，
window.onscroll=function(){};
注意在获取滚动条距离的时候
谷歌不识别document.documentElement.scrollTop，必须要加上document.body.scrollTop；即
var scrolltop=document.documentElement.scrollTop||document.body.scrollTop;
这样才能兼容各个浏览器！
代码如下:
<!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>自学php网</title>
<style type="text/css">
#box{ height:50px; width:200px; background:#666; position:absolute; left:0px; top:0px;}
</style>
</head>
<body style="height:9000px;">
<div id="box"></div>
<script language="javascript">
window.onscroll = function(e){
var e =e || window.event;
var scrolltop=document.documentElement.scrollTop||document.body.scrollTop;
var box = document.getElementById('box');
box.style.top = scrolltop+'px';
//console.log(scrolltop);
}
</script>
</body>
</html>
