<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>JS——伸縮菜單</title>
<style>
ul , h2 { padding:0; margin:0; }
li { list-style:none; }
#list { width:240px; border:1px solid #ccc; border-top:none; margin:0 auto; }
#list h2 { font-size:14px; border-top:1px solid #ccc; height:30px; line-height:30px; text-indent:20px; background:url(images/arr1.gif) no-repeat 5px center #eee; color:#000; cursor:pointer;}
#list .active { background:url(images/arr2.gif) no-repeat 5px center #ddd; color:#000; }
#list ul { display:none; }
#list ul li { line-height:24px; border-top:1px solid #ccc; text-indent:24px; }
#list ul .hover { background:#6FF; }
</style>
<script>
window.onload = function(){
var oUl = document.getElementById('list');
var aH2 = oUl.getElementsByTagName('h2');
var aUl = oUl.getElementsByTagName('ul');
for(var i = 0; i<aH2.length; i++){
aH2[i].index = i;
aH2[i].onclick = function(){
if(this.className == ''){
aUl[this.index].style.display = 'block';
this.className = 'active';
}else{
aUl[this.index].style.display = '';
this.className = '';
}
};
}
};
</script>
</head>
<body>
<ul id="list">
<li class="lis">
<h2>我的好友</h2>
<ul>
<li>張三</li>
<li>張三</li>
<li>張三</li>
<li>張三</li>
</ul>
</li>
<li class="lis">
<h2>企業好友</h2>
<ul>
<li>李四</li>
<li>李四</li>
<li>李四</li>
<li>李四</li>
<li>李四</li>
</ul>
</li>
<li class="lis">
<h2>黑名單</h2>
<ul>
<li>阿貓</li>
<li>阿狗</li>
</ul>
</li>
</ul>
</body>
</html>思路：
1.獲取相關元素
2.循環遍歷所有的H2，併爲每個H2添加索引
3.爲每個H2添加點擊事件，通過H2當前的className判斷是否爲空來顯示隱藏ul，或添加刪除當前H2的className