例1，
<!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>
<title>自动固定顶部的悬浮菜单栏代码_www.jb200.com</title>
<meta http-equiv="content-type" content="text/html;charset=gb2312">
<style type="text/css">
*{margin:0;padding:0;}
ul,li{list-style:none;}
#content{width:600px;margin:0 auto;border:1px solid #f00;}
ul li.item{width:400px;text-align:center;margin:20px 100px;background:#00f;color:#fff;font-size:14px;font-weight:bold;height:100px;line-height:100px;}
#float_banner{position:absolute;top:0;left:50%;width:900px;margin-left:-450px;height:30px;line-height:30px;text-align:center;background:#000;color:#fff;font-size:14px;font-weight:bold;z-index:2;}
</style>
</head>
<body>
<div id="float_banner">这里是顶部的横幅，随着页面滚动而浮动</div>
<ul id="content">
<li class="item">第一块内容</li>
<li class="item">第二块内容</li>
<li class="item">第三块内容</li>
<li class="item">第四块内容</li>
<li class="item">第五块内容</li>
<li class="item">第六块内容</li>
<li class="item">第七块内容</li>
<li class="item">第八块内容</li>
<li class="item">第九块内容</li>
<li class="item">第十块内容</li>
</ul>
<script language="javascript">
var speed = 100;
var scrollTop = null;
var hold = 0;
var float_banner;
var pos = null;
var timer = null;
var moveHeight = null;
float_banner = document.getElementById("float_banner");
window.onscroll=scroll_ad;
function scroll_ad(){
scrollTop = document.documentElement.scrollTop+document.body.scrollTop;
pos = scrollTop - float_banner.offsetTop;
pos = pos/10
moveHeight = pos>0?Math.ceil(pos):Math.floor(pos);
if(moveHeight!=0){
float_banner.style.top = float_banner.offsetTop+moveHeight+"px";
setTimeout(scroll_ad,speed);
}
//alert(scrollTop);
}
</script>
</body>
</html>
例2，
<!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>顶部固定菜单_www.jb200.com</title>
<style type="text/css">
*{ margin:0; padding:0;}
.nav-wrapper-fixed{ position:fixed; top:0; width:100%;}
.nav-wrapper-fixed .nav{width:960px; margin:0 auto;}
.nav-wrapper-fixed .nav li{ float:left; width:100px; margin-right:5px; background:#CCC; text-align:center; height:24px; line-height:24px; list-style:none;}
.nav-wrapper{ margin-top:100px; width:100%;}
.nav-wrapper .nav{width:960px; margin:0 auto;}
.nav-wrapper .nav li{ float:left; width:100px; margin-right:5px; background:#CCC; text-align:center; height:24px; line-height:24px; list-style:none;}
</style>
<script type="text/javascript">
window.onload = function () {
var nav = document.getElementById('nav');
var navFixed = document.getElementById('navFixed');
window.onscroll = function () {
var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
document.title = scrollTop
if (scrollTop > nav.offsetTop) {
navFixed.style.display = 'block';
} else if (scrollTop < nav.offsetTop) {
navFixed.style.display = 'none';
}
}
};
</script>
</head>
<body style="height:2000px;">
<div class="nav-wrapper">
<div class="nav" id="nav">
<ul>
<li>菜单一</li>
<li>菜单二</li>
<li>菜单三</li>
<li>菜单四</li>
<li>菜单五</li>
</ul>
</div>
</div>
<div class="nav-wrapper-fixed" id="navFixed" style="display:none;">
<div class="nav" id="nav">
<ul>
<li>菜单一</li>
<li>菜单二</li>
<li>菜单三</li>
<li>菜单四</li>
<li>菜单五</li>
</ul>
</div>
</div>
</body>
</html>
例3，
$(function () {
var elm = $('#pordAttr');
var startPos = $(elm).offset().top;
$.event.add(window, "scroll", function () {
var p = $(window).scrollTop();
$(elm).css('position', ((p) > startPos) ? 'fixed' : 'static');
$(elm).css('top', ((p) > startPos) ? '0px' : "");
});
});
说明：
获取元素（这里定位元素A）距离顶部的高度，接着设定scroll滚动的事件，比如超过那个高度，把A的位置设定为fixed，小于该高度，修改回relative。
建议大家亲自测试一下以上的三段代码，看看哪个更适合自己。