jquery实现的超出屏幕时把固定层变为定位层的代码

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我是靠谱客的博主贪玩奇异果，最近开发中收集的这篇文章主要介绍jquery实现的超出屏幕时把固定层变为定位层的代码，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

非常好的一个用户体验实例。如果不明白的话就看下面的图片吧

淘宝产品列表 http://search1.taobao.com/browse/50010388/…
taobao浮动层实例

腾讯财经产业经济 http://finance.qq.com/industry/index.htm

如何实现？
scrollTop是什么？当元素内部的内容高度超过元素本身的高度时就会出现滚动条，随着拖动滚动条而被隐去的上面部分的高度就是scrollTop值。
这种定位层就是当页面触发onscroll事件时，取得scrollTop值并写入定位层CSS属性，使之保持位置。
下面是实例代码

复制代码代码如下:

 
<!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=gb2312" /> 
<title>定位层</title> 
<script type="text/javascript" src="http://img.uoften.com/jslib/jquery/jquery.js"></script> 
<style type="text/css"> 
body{padding:10px;margin:0;} 
#box{width:960px;margin:0 auto;} 
#box1{width:250px;height:25px;position:relative;} 
#box1_1{width:250px;height:25px;line-height:25px;background:#f00;color:#fff;} 
p{font-size:24px;margin:10px 0;} 
</style> 
<script type="text/javascript"> 
function tools(){ 
var top=$(document).scrollTop(); 
if(($.browser.msie==true)&&($.browser.version==6.0)){ 
if(top>168)$("#box1_1").css({position:"absolute",top:top-168}); 
}else{ 
if(top>168)$("#box1_1").css({position:"fixed",top:"-"&top+"px"}); 
} 
if(top<=168)$("#box1_1").css({position:"static",top:0}); 
} 
$(function(){ 
window.onscroll=tools; 
window.onresize=tools; 
}); 
</script> 
</head> 
<body> 
<div id="box"> 
<p>往下拖动滚动条↓<a href="http://www.uoften.com">uoften.com</a> <a href="http://www.uoften.com">脚本之家</a></p> 
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<div id="box1"><div id="box1_1">这里是定位层</div></div> 
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</div> 
</body> 
</html> 