为什么按照老师的代码写完以后，底端有闪烁，我还是有bug

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<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>多级下拉菜单</title>
    <style type="text/css">

        #navmenu{
           list-style: none;  
        }
        #navmenu li{
            float: left;
            height: 40px;
            padding: 0;
            position: relative;
        }
        #navmenu li a{
            text-decoration: none;
            padding: 0 10px;
            width: 94px;
            text-align: center;
            display: block;
            height: 40px;
            line-height: 40px;
            background-color: #111111;
            color:#ffffff;
        }
        #navmenu li ul{
            height: 0;
            list-style: none;
            display: none;
            position: absolute;
            left: 0;
            top: 40px;
            padding: 0;
            overflow: hidden;
        }
        #navmenu li ul li{
            display:block;
            float: left;
        }
        #navmenu li a:hover{
            border-radius: 6px;
            background:url(images/slide-pannel_14.png) 0 0 repeat-x;
            box-shadow: 0 2px 0 #e4393c;
        }

        .note{
            color:#eee;
            display: block;
            background:url(images/slide-pannel_14.png) 0 0 repeat-x;
        }
        .corner{
            display: block;
            margin-top: 3px;
            height: 11px;
            background: url(images/bird.png) 47px 0 no-repeat;
        }
    </style>
</head>

<script type="text/javascript">
     window.onload=function(){
        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";
                        AddH(u.id);
                    }; 
                };
                lis[i].onmouseout=function(){
                    var u=this.getElementsByTagName('ul')[0];
                    if (u!=undefined) {   
                        SubH(u.id);
                    }
                };
            };
    };
    function AddH(id){
        var uls=document.getElementById(id);
        var h=uls.offsetHeight;
        h+=1;
        if (h<137) {
            uls.style.height=h+"px";
            setTimeout("AddH('"+id+"')",20);
        }else{
            return;
        };
    };
    function SubH(id){
        var uls=document.getElementById(id);
        var h=uls.offsetHeight;
        h-=1;
        if (h>0) {
            uls.style.height=h+"px";
            setTimeout("SubH('"+id+"')",20);
        }else{
            uls.style.display="none";
            return;
        };
    }

</script>
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</html>
DDjx
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1回答

DDjx
我觉得是没有清除计时器的原因
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