javascript简单的选项卡

实现一个简单的选项卡功能
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>一个选项卡</title>
    <style type = "text/css">
        *{
            padding:0;
            margin:0;
        }
        #main {
            width:600px;
            height:300px;
            background:white;
            border:2px solid red;
            position:relative;
            margin:50px auto;
        }
        ul {
            height:49px;
            background:grey;
            font-size:30px;
            line-height:49px;
            color:red;
            list-style-type:none;
            border-bottom:1px dotted grey;
        }
        li {
            width:200px;
            float:left;
            text-align:center;
        }
        li#active{
            background:white;
        }
        p {
            font-size:40px;
            text-align:center;
        }
        .content>div {
            display:none;
        }
        .content>div#play {
            display:block;
            height:250px;
            background:red;
        }



    </style>
</head>
<body>
    <div id = "main">
        <ul class = "lis">
            <li id="active">电影</li>
            <li>娱乐</li>
            <li>数码</li>
        </ul>
        <div class = "content">
            <div id = "play" class="action">
                <p>
                    this is a movie
                </p>
            </div>
            <div class="action">
                <p>
                    this is about entertainment
                </p>
            </div>
            <div class="action">
                <p>
                    this is about digital product
                </p>
            </div>
        </div>
    </div>
</body>
    <script type = 'text/javascript'>
        var lis = document.getElementsByTagName("li");
        var con = document.getElementsByClassName("action");
        for(var i = 0; i < lis.length; i++){
            lis[i].index = i;
            lis[i].onclick = function(){
                for(var j = 0; j < lis.length; j++){
                lis[j].id = "";
                con[j].id = "";
            }
                this.id = "active";
                con[this.index].id = "play"
            }
        }
    </script>
</html>