看似简单的一个菜单，确需要不少的知识点
1. getByClass
getElementsByClassName 已经有大部分现代浏览器支持了，只有ie6,ie7,ie8是不支持的。所以对ie6,7,8做特别的处理就行，而ie里边有个内置的属性一直被我们所忽略，document.all，这个比一般的document.getElementsByTagName('*')或许要快一点。
2. setTimeout 的巧妙用法。
当鼠标离开某个区域时，延时隐藏另外一个区域，而到另外一个区域是清除这个定时器。
<!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" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=UTF-8"/>
<title>二级延迟菜单 - 豪情</title>
<style type="text/css">
*{margin:0;padding:0;}
body{font:12px/1.125 Arial,Helvetica,sans-serif;background:#333;}
table{border-collapse:collapse;border-spacing:0;}
li{list-style:none;}
a:focus,input,textarea{outline-style:none;}
input[type="text"],input[type="password"],textarea{outline-style:none;-webkit-appearance:none;}
a{color:#0a8cd2;text-decoration:none;}
a:hover{text-decoration:underline;}
.none{display:none}
.demo{600px;height:500px;margin:30px auto;padding:30px;border:5px solid #ccc;background:#fff;}
.main_nav{404px;height:30px;margin:0 auto;}
.main_nav ul li{float:left;100px;height:30px;border-right:1px solid #666;position:relative;}
.main_nav ul li a{display:block;height:30px;line-height:30px;text-align:center;background:#333;color:#ccc;text-decoration:none;}
.submenu{position:absolute;left:0;top:30px;100px;display:none;}
.submenu dd{height:31px;}
.main_nav ul li dd a{display:block;height:30px;line-height:30px;text-align:center;color:#ccc;background:#333;border-bottom:1px solid #666;}
.main_nav ul li dd a:hover{background:#555;color:#fff;}
</style>
</head>
<body>
<div id="content" class="demo">
<div class="main_nav hover">
<ul>
<li><a class="link" href="javascript:" title="">关于我们</a>
<dl class="submenu">
<dd><a href="javascript:" title="">栏目子导航1</a></dd>
<dd><a href="javascript:" title="">栏目子导航1</a></dd>
<dd><a href="javascript:" title="">栏目子导航1</a></dd>
<dd><a href="javascript:" title="">栏目子导航1</a></dd>
<dd><a href="javascript:" title="">栏目子导航1</a></dd>
</dl>
</li>
<li><a class="link" href="javascript:" title="">新闻中心</a>
<dl class="submenu">
<dd><a href="javascript:" title="">栏目子导航2</a></dd>
<dd><a href="javascript:" title="">栏目子导航2</a></dd>
<dd><a href="javascript:" title="">栏目子导航2</a></dd>
<dd><a href="javascript:" title="">栏目子导航2</a></dd>
<dd><a href="javascript:" title="">栏目子导航2</a></dd>
</dl>
</li>
<li><a class="link" href="javascript:" title="">联系我们</a>
<dl class="submenu">
<dd><a href="javascript:" title="">栏目子导航3</a></dd>
<dd><a href="javascript:" title="">栏目子导航3</a></dd>
<dd><a href="javascript:" title="">栏目子导航3</a></dd>
<dd><a href="javascript:" title="">栏目子导航3</a></dd>
<dd><a href="javascript:" title="">栏目子导航3</a></dd>
</dl>
</li>
<li><a class="link" href="javascript:" title="">雁过留声</a>
<dl class="submenu">
<dd><a href="javascript:" title="">栏目子导航4</a></dd>
<dd><a href="javascript:" title="">栏目子导航4</a></dd>
<dd><a href="javascript:" title="">栏目子导航4</a></dd>
<dd><a href="javascript:" title="">栏目子导航4</a></dd>
<dd><a href="javascript:" title="">栏目子导航4</a></dd>
</dl>
</li>
</ul>
</div>
</div>
<script type="text/javascript">
(function(window){
/**
* getElementsByClassname
* @param oParent parent ele
* @param cls classname
* @return {*}
*/
function getByClass(oParent, cls){
if(document.getElementsByClassName){
return (oParent || document).getElementsByClassName(cls);
} else {
oParent = oParent || document;
var res = [],
child = null,
reg = new RegExp('(^|\s)' + cls + '(\s|$)', 'i');
for(var i = 0, len = oParent.all.length; i < len; i ++){
child = oParent.all[i];
if(reg.test(child.className)){
res.push(child);
}
}
return res;
}
}
var content = document.getElementById('content'),
oA = getByClass(content, 'link'),
child = null,
timer = null,
oDl = getByClass(content, 'submenu');
for(var i = 0, len = oA.length; i < len; i++){
child = oA[i];
child.index = i;
child.onmouseover = function(){
for(var j = 0; j < len; j++){
oDl[j].style.display = 'none';
}
oDl[this.index].style.display = 'block';
clearTimeout(timer); // 清除从 dl 移回时的定时器
}
child.onmouseout = function(){
var that = this;
timer = setTimeout(function(){
oDl[that.index].style.display = 'none';
}, 500);
}
oDl[i].onmouseover = function(){
clearTimeout(timer);
}
oDl[i].onmouseout = function(){
var that = this;
timer = setTimeout(function(){
that.style.display = 'none';
}, 500);
}
}
}(window));
</script>
</body>
</html>