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                            /JavaScript
                        
                        /形形色色的下拉菜单

代码没报错但是为什么二级菜单的高度停在3px就不动了呢？求解各位大神~~~~

<!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 charset="utf-8" />
<title></title>
<style type="text/css">
.top-nav
{
font-size: 14px;
font-weight: bold;
list-style: none;
}
.top-nav li
{
float: left;
margin-right: 1px;
}
.top-nav li a
{
line-height: 34px;
text-decoration: none;
background: #3f240e;
color: #fff;
display: block;
width: 80px;
text-align: center;
}
.top-nav ul:after,.top-nav ul:before{
content:"";
display:block;
height: 0;
}
.top-nav ul:after{
clear:both;
}
.top-nav ul
{
zoom:1;
list-style: none;
/* display: block; */
padding: 0;
position: absolute;
height: 0;
overflow: hidden;
}
.top-nav ul li{
float:left;
}

.top-nav li a:hover
{
background: url(http://img1.sycdn.imooc.com//5461b50d0001e28000010034.jpg) 0 0 repeat-x;
}
.note
{
color: #3f240e;
display: block;
background: url(http://img1.sycdn.imooc.com//5461b50d0001e28000010034.jpg) 0 0 repeat-x;
}
.corner
{
display: block;
height: 11px;
background: url(http://img1.sycdn.imooc.com//5461b5620001410d00170011.jpg) 31px 0 no-repeat;
}
</style>
<script type="text/javascript">
var t; //将这里的定义放在函数中声明将产生抖动（未清理定时器）
window.onload = function () {
//鼠标经过时的效果
//bug: 鼠标多次快速移动导致子菜单抖动 ok 抖动未清除setTimeout
var Lis = document.getElementsByTagName("li");
for(var i=0,len=Lis.length; i<len; i++){
Lis[i].onmousemove = function(){
var u = document.getElementById('mnuUL');
//var tmove,tleave;
if(u!=undefined)
clearTimeout(t);
ChangeH(u.id,1);
}
Lis[i].onmouseleave = function () {
var u = document.getElementById('mnuUL');

if (u != undefined)
clearTimeout(t);
ChangeH(u.id,-1);
}
}
}

function ChangeH(id, count) {
// 根据ID找到ulList，同时得到其高度
var ulList = document.getElementById(id);
var h = ulList.offsetHeight;
//var t = null;
clearTimeout(t);
h += count;
if (count > 0) {
if (h <= 42) {
// 将高度赋值给ulList，同时，不断调用本函数
ulList.style.height = h + "px";
//tmove = setTimeout("ChangeH('" + id + "',1)", 10);
t = setTimeout("ChangeH('" + id + "',1)", 10);
}
else {
return;
}
}
else {
if (h > 0) {
// 将高度赋值给ulList，同时，不断调用本函数
ulList.style.height = h + "px";
//tleave = setTimeout("ChangeH('" + id + "',-1)", 10);
t = setTimeout("ChangeH('" + id + "',-1)", 10);
}
else {
//ulList.style.display = "none";
return;
}
}
}
</script>
</head>
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