二级菜单动画显示效果-原创手记-慕课网

<!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></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">
    var t;
    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){
                   clearTimeout(t);
                   u.style.display="block";
                   ChangeH(u.id,+1);
               }
           }
            Lis[i].onmouseleave = function () {
                var u = this.getElementsByTagName("ul")[0];
                if (u != undefined) {
                    ChangeH(u.id,-1);
                    clearTimeout(t);
                }
            }
       }
        }

    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;

        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;
            }
        }
        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);
            }
            else {
                ulList.style.display = "none";
                return;
            }
        }
    }
</script>

</head>
<body>
<ul class="top-nav">
<li><a href="#"><span class="note">慕课网</span></a> </li>
<li><a href="#">课程大厅</a> </li>
<li><a href="#">学习中心</a>
<ul id="mnuUL">
<span class="corner"></span>
<li><a href="#">前端课程 </a></li>
<li><a href="#">手机开发</a> </li>
<li><a href="#">后台编程</a></li>
</ul>
</li>
<li><a href="#">关于我们</a></li>
</ul>
</body>
</html>