原生js实现跑马灯抽奖效果

目前好多的微信活动都有一些抽奖活动，其中就有跑马灯。
<!DOCTYPE html>

<html>

<head>

<title>跑马灯效果</title>

<style>

table .pao{

    border:1px solid #e5e5e5;

    padding:10px 20px;

}

table .on{

    border-color:red;

    color:red;

}

</style>

<script>

window.onload = function(){

    var paomadeng = {

        currentIndex : 1, //当前索引

        indexCount : 12, //个数

        timer : 0, //定时器

        currentCycle : 0, //当前圈数

        cycles : 4, //跑的圈数

        speed : 400, //速度，即定时器的时间间隔

        key : 0, //钥匙,随机数

        btn : 0, //触发按钮

        classPrefix : "pao-", //元素类名class前缀

        reset : function(){

            //触发对象

            paomadeng.btn = this;

            paomadeng.btn.style.display = "none";

            clearInterval(paomadeng.timer);

            paomadeng.currentCycle = 0;

            paomadeng.speed = 400;

            paomadeng.key = Math.ceil(Math.random() * paomadeng.indexCount);

            console.log("key:" + paomadeng.key);

            paomadeng.run();

        },

        run : function(){

            console.log("speed:" + paomadeng.speed);

            var before = paomadeng.currentIndex == 1 ? paomadeng.indexCount : paomadeng.currentIndex - 1;

            //设置上一索引的类名

            var beforeNode = document.getElementsByClassName(paomadeng.classPrefix + before)[0];

            var beforeClassNewName = beforeNode.className.replace("on","");

            beforeNode.className = beforeClassNewName;

            //设置当前索引的类名

            var currentNode = document.getElementsByClassName(paomadeng.classPrefix + paomadeng.currentIndex)[0];

            currentNode.className += " on"; //注意前面有空格

            paomadeng.upSpeed();

            paomadeng.downSpeed();

            paomadeng.currentIndex += 1;

            paomadeng.currentIndex = paomadeng.currentIndex > paomadeng.indexCount ? 1: paomadeng.currentIndex;

        },

        //加速

        upSpeed : function(){

            //前2圈且speed>100时加速

            if(paomadeng.currentCycle < 2 && paomadeng.speed > 100){

                paomadeng.speed -= 5 * paomadeng.currentIndex ;

                paomadeng.stop();

                paomadeng.start();

            }

        },

        //增加圈数 并 减速

        downSpeed : function(){

            //增加圈数

            if(paomadeng.currentIndex == paomadeng.indexCount){

                paomadeng.currentCycle += 1;

            }

            //如果当前所跑圈数小于总圈数-1 并且 速度小于400，那么减速

            if(paomadeng.currentCycle > paomadeng.cycles-1 && paomadeng.speed < 400){

                paomadeng.speed += 20;

                paomadeng.stop();

                paomadeng.start();

            }

            //如果当前所跑圈数大于总圈数 且 索引值等于key，那么停止奔跑

            if(paomadeng.currentCycle > paomadeng.cycles && paomadeng.currentIndex == paomadeng.key){

                paomadeng.stop();

                paomadeng.showPrize();

            }

        },

        stop : function(){

            clearInterval(paomadeng.timer);

        },

        start : function(){

            paomadeng.timer = setInterval(paomadeng.run , paomadeng.speed);

        },

        showPrize : function(){

            //过一会再显示提示信息

            setTimeout(function(){

                alert("恭喜，你中了" + paomadeng.key + "等奖");

                paomadeng.btn.style.display = "block";

            },700);

        }

    };

    document.getElementById("startPao").onclick= paomadeng.reset;

};

</script>

</head>

<body>

<div class="container">

<table>

    <tr>

        <td class="pao pao-1">1</td>

        <td class="pao pao-2">2</td>

        <td class="pao pao-3">3</td>

        <td class="pao pao-4">4</td>

    </tr>

    <tr>

        <td class="pao pao-12">12</td>

        <td class="pao"></td>

        <td class="pao"></td>

        <td class="pao pao-5">5</td>

    </tr>

    <tr>

        <td class="pao pao-11">11</td>

        <td class="pao"></td>

        <td class="pao"></td>

        <td class="pao pao-6">6</td>

    </tr>

    <tr>

        <td class="pao pao-10">10</td>

        <td class="pao pao-9">9</td>

        <td class="pao pao-8">8</td>

        <td class="pao pao-7">7</td>

    </tr>

</table>

<br/>

<input type="button" value="开始跑" id="startPao" />

</div>

</body>

</html>