当我鼠标划过学习中心 会出现二级菜单 可是当我划过学习中心， 而二级菜单还没有显示完全， 很快把它在移动到别的链接上然后再移回学习中心。而导致二级菜单显示没有完成使得其菜单卡在那里。。请问这个bug 怎么解决啊
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<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<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
{
list-style: none;
display: none;
padding: 0;
position: absolute;
height: 0;
overflow: hidden;
}
.top-nav li a:hover
{
background: url(http://img.mukewang.com/5461b50d0001e28000010034.jpg) 0 0 repeat-x;
}
.note
{
color: #3f240e;
display: block;
background: url(http://img.mukewang.com/5461b50d0001e28000010034.jpg) 0 0 repeat-x;
}
.corner
{
display: block;
height: 11px;
background: url(http://img.mukewang.com/5461b5620001410d00170011.jpg) 31px 0 no-repeat;
}
</style>
<script type="text/javascript">
window.onload = function () {
//鼠标经过时的效果
var Lis=document.getElementsByTagName("li") ;
for(var i=0;i<Lis.length;++i){
Lis[i].onmouseover = function () {
var u = this.getElementsByTagName("ul")[0];
if (u != undefined) {
u.style.display="block";
ChangeH(u.id,1);
}
}
Lis[i].onmouseleave = function () {
var u = this.getElementsByTagName("ul")[0];
if (u != undefined) {
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function ChangeH(id, count) {
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var ulList = document.getElementById(id);
var h = ulList.offsetHeight;
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";
setTimeout("ChangeH('" + id + "',1)", 10);
}
else {
return;
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}
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";
setTimeout("ChangeH('" + id + "',-1)", 10);
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ulList.style.display = "none";
return;
}
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}
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<body>
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