tab.html

<!doctype html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style type="text/css">
    * {
      margin: 0;
      padding: 0;
      font-size: 13px;
      list-style: none;
    }

    .menu {
      width: 210px;
      margin: 50px auto;
      border: 1px solid #ccc;
    }

    .menu p {
      height: 25px;
      line-height: 25px;
      font-weight: bold;
      background: #eee;
      border-bottom: 1px solid #ccc;
      cursor: pointer;
      padding-left: 5px;
    }

    .menu div ul {
      display: none;
    }

    .menu li {
      height: 24px;
      line-height: 24px;
      padding-left: 5px;
    }
  </style>
  <script type="text/javascript">
    window.onload = function () {

      // 将所有点击的标题和要显示隐藏的列表取出来
      var titles = document.getElementsByTagName("p");
      var divs = document.getElementsByTagName("ul")
      console.log(divs)
      console.log(titles)
      // 遍历所有要点击的标题且给它们添加索引及绑定事件
      for (var i = 0; i < titles.length; i++) {
        titles[i].id = i;
        titles[i].onclick = function () {
          //alert(this.id)
          // 获取点击的标题上的索引属性，根据该索引找到对应的列表
          var p = divs[this.id]
          // 判断该列表，如果是显示的则将其隐藏，如果是隐藏的则将其显示出来
          if (p.style.display == "block") {
            p.style.display = "none"
          } else {
            for (var j = 0; j < divs.length; j++) {
              divs[j].style.display = "none"
            }
            p.style.display = "block"
          }
        }
      }


    }
  </script>
</head>

<body>
  <div class="menu" id="menu">
    <div>
      <p>Web前端</p>
      <ul style="display:block">
        <li>JavaScript</li>
        <li>DIV+CSS</li>
        <li>jQuery</li>
      </ul>
    </div>
    <div>
      <p>后台脚本</p>
      <ul>
        <li>PHP</li>
        <li>ASP.net</li>
        <li>JSP</li>
      </ul>
    </div>
    <div>
      <p>前端框架</p>
      <ul>
        <li>Extjs</li>
        <li>Esspress</li>
        <li>YUI</li>
      </ul>
    </div>
  </div>
</body>

</html>