<ul id="list">
 <li class="lis">
  <h2>我的好友</h2>
  <ul>
   <li>张三</li>
   <li>李四</li>
   ...
  </ul>
 </li>
 <li class="lis">
  <h2>企业好友</h2>
  <ul>
   <li>小明</li>
   <li>小红</li>
   ...
  </ul>
 </li>
 <li class="lis">
  <h2>黑名单</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;/*文字缩进20px*/
 background: url(img/ico1.gif) no-repeat 5px center pink;/*前面小箭头*/
 cursor: pointer;
}
#list .active { /* 点击时添加的类名 */
 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;/*文字缩进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进行匹配，所以我们要用索引值，给h2身上添加索引值
 for(var i=0;i<ah2.length;i++){    
  ah2[i].index = i;//给h2添加索引值，点击谁就给谁添加索引值
  ah2[i].onclick = function(){
   if(this.className == ''){//判断所点击的h2标签是否有类，
    //this.index指h2身上的索引数，this指h2，h2的索引值为this.index
    uls[this.index].style.display = 'block'; 
    this.className = 'active';//给当前点击的h2添加类，更改箭头方向
   }else{
    uls[this.index].style.display = 'none';
    this.className = '';
   }
  }
 }
}