jQuery固定在网页顶部的菜单

答案：<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>固定在顶部的菜单</title>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
<script type="text/javascript">
$(function(){	
	//获取要定位元素距离浏览器顶部的距离
	var navH = $(".nav").offset().top;
	//滚动条事件
	$(window).scroll(function(){
		//获取滚动条的滑动距离
		var scroH = $(this).scrollTop();
		//滚动条的滑动距离大于等于定位元素距离浏览器顶部的距离，就固定，反之就不固定
		if(scroH>=navH){
			$(".nav").css({"position":"fixed","top":0,"left":"50%","margin-left":"-200px"});
		}else if(scroH<navH){
			$(".nav").css({"position":"static","margin":"0 auto"});
		}
		console.log(scroH==navH);
	})
})
</script>
<style type="text/css">
*{ margin:0px; padding:0px;}

.top{
	height:900px;
	background:#009999;
	}
	
.nav{
	width:400px;
	margin:0 auto;
	border-bottom:1px solid #F00;
	}
	
.nav ul:after{
	clear:both;
	content:"";
	display:table;}
	
.nav ul li{
	background:#FFFFFF;
	float:left;
	width:70px;
	border:2px solid #06F;
	text-align:center;
	height:28px;
	line-height:28px;}	
.cl01,.cl02,.cl03,.cl04,.cl05,.cl06,.cl07,.cl08{
	height:300px;}	
.cl01{
	background:#333;}	
.cl02{
	background:#F00;}
.cl03{
	background:#FFFF00;}	
.cl04{
	background:#0FF;}	
.cl05{
	background:#030;}
.cl06{
	background:#006699;}
.cl07{
	background:#930;}
.cl08{
	background:#969;}
</style>
</head>
<body>
<div class="top"></div>
<div class="nav">
	<ul>
		<li>测试1</li>
		<li>测试2</li>
		<li>测试3</li>
		<li>测试4</li>
	</ul>
</div>
<div class="cl01"></div>
<div class="cl02"></div>
<div class="cl03"></div>
<div class="cl04"></div>
<div class="cl05"></div>
<div class="cl06"></div>
<div class="cl07"></div>
<div class="cl08"></div>
</body>
</html>
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