<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container {
            width: 600px;
            height: 600px;
            border: 1px solid;
            display: flex;
            flex-wrap: wrap;
            margin: 100px auto;
        }

        .block {
            width: 33.33%;
            height: 33.33%;
            outline: 1px solid black;
            text-align: center;
            line-height: 200px;
            font-size: 26px;
        }

        .block5 {
            background-color: skyblue;
            cursor: pointer;
        }
    </style>
</head>
<body>
     <div class="container">
        <div class="block1 block">小米笔记本</div>
        <div class="block2 block">iPhoneX</div>
        <div class="block3 block">PS4游戏机</div>
        <div class="block4 block">谢谢参与</div>
        <div class="block5 block">开始抽奖</div>
        <div class="block6 block">索尼电视机</div>
        <div class="block7 block">西门子冰箱</div>
        <div class="block8 block">老板抽油烟机</div>
        <div class="block9 block">空气净化机</div>
    </div>
    <script>
        var blocks = document.getElementsByClassName("block");
        // 数组存放的是盒子的下标，按照顺时针的顺序
        var arr = [0, 1, 2, 5, 8, 7, 6, 3], i = 0, count = 0, stopTimer;
        var rand = Math.floor(Math.random() * 8 + 50); // 给出一个停止计时器的随机数 count的值等于这个随机数时停止计时器
        var around = function () {
            // 将其他盒子都变为白色
            for (var j = 0; j < arr.length; j++) {
                blocks[arr[j]].style.background = "white";
            }
            // 这里blocks的取值为 blocks[0] blocks[1] blocks[2] blocks[5] blocks[8] blocks[7] blocks[6] blocks[3]
            // 将当前arr[i]值所对应的盒子修改为粉色
            blocks[arr[i]].style.background = "pink";
            i++; 
            // 重制i的值
            if (i === arr.length) {
                i = 0;
            }
            count++; // count是一个计数器 根据count的值来调整速度
            // 下面的4个if根据count的值来关闭计时器和重启计时器 改变计时器的时间间隔
            if (count === 5 || count === 45) {
                clearInterval(stopTimer);
                stopTimer = setInterval(around, 200);
            }
            if (count === 10 || count === 35) {
                clearInterval(stopTimer);
                stopTimer = setInterval(around, 100);
            }
            if (count === 15) {
                clearInterval(stopTimer);
                stopTimer = setInterval(around, 50);
            }
            // 当等于上面的随机数时，停止计时器
            if (count === rand) {
                clearInterval(stopTimer);
            }
        }
        // 给开始按钮绑定点击事件 点击后执行 around 
        var start = function () {
            blocks[4].removeEventListener("click", start); // 当用户点击了开始按钮后 必须要移除该事件 防止用户重复点击
            stopTimer = setInterval(around, 300);
        }
        blocks[4].addEventListener("click", start);
    </script>
</body>
</html>