<ul id="list"> <li class="lis">  <h2>我的好友</h2>  <ul>   <li>張三</li>   <li>李四</li>   ...  </ul> </li> <li class="lis">  <h2>企業好友</h2>  <ul>   <li>小明</li>   <li>小紅</li>   ...  </ul> </li> <li class="lis">  <h2>黑名單</h2>  <ul>   <li>哈哈</li>   ...  </ul> </li></ul>

ul,h2 {padding: 0;margin: 0;}li {list-style: none;}#list { width: 240px; border: 1px solid #ccc; margin: 0 auto;}#list .lis { }#list h2 { height: 30px; line-height: 30px; text-indent: 20px;/*文字縮進20px*/ background: url(img/ico1.gif) no-repeat 5px center pink;/*前面小箭頭*/ cursor: pointer;}#list .active { /* 點擊時添加的類名 */ background: url(img/ico2.gif) no-repeat 5px center #ff9;}#list ul {display: none;}#list ul li { line-height: 24px; border-bottom: 2px solid #fc4; text-indent: 24px;/*文字縮進24px*/}

window.onload = function(){    var list = document.getElementById('list');    var ah2 = list.getElementsByTagName('h2');    var uls = list.getElementsByTagName('ul'); // h2要和下面的ul進行匹配，所以我們要用索引值，給h2身上添加索引值 for(var i=0;i<ah2.length;i++){      ah2[i].index = i;//給h2添加索引值，點擊誰就給誰添加索引值  ah2[i].onclick = function(){   if(this.className == ''){//判斷所點擊的h2標簽是否有類，    //this.index指h2身上的索引數，this指h2，h2的索引值為this.index    uls[this.index].style.display = 'block';     this.className = 'active';//給當前點擊的h2添加類，更改箭頭方向   }else{    uls[this.index].style.display = 'none';    this.className = '';   }  } }}