JavaScript——鼠标点击事件

//第一个盒子<div id="box1"><a href="###">点击我出现蓝盒子</a></div>//第二个盒子<div id="box2"></div>//javascript脚本      <script type="text/javascript">    var a = document.getElementsByTagName('a')[0],        box2 = document.getElementById('box2'),        flag = 1;    a.onclick = function () {        if(flag){            box2.style.display = 'block';            flag = 0;        }else {            box2.style.display = 'none';            flag = 1;        }    }</script>//样式如下        <style type="text/css">
        *{margin: 0; padding: 0;}
        div{width: 100px; height: 100px;}
        #box1{background-color: red;}
        #box2{background-color: blue; display: none;}
    </style>