九宫格转圈圈抽奖活动，有加速，减速效果

在线访问demo和代码在底部

代码，复制就可以跑

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

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>🐯🐯🐯</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .box {
            position: relative;
            width: 300px;
            height: 300px;
            border: 1px solid grey;
        }

        .item {
            width: 80px;
            height: 80px;
            position: absolute;
            background-color: gainsboro;
            display: flex;
            justify-content: center;
            align-items: center;
        }

        .item.active {
            background-color: red;
            font-weight: 600;

        }
    </style>
</head>

<body>
    <h1 id="result">这一次结果</h1>
    <div class="box" id="box"></div>
    <button id="start">开始</button>
    <script>
        let box = document.querySelector("#box")
        let start = document.querySelector("#start")
        let result = document.querySelector("#result");
        //奖项个数
        const itemLen = 8;
        let arr = [];
        //开启位置
        let startIndex = 0;
        let timer = null;
        let speed = 80;

        //随机工具函数
        function getRandomNumber(min, max) {
            return Math.floor(Math.random() * (max - min + 1)) + min;
        }
        //基础圈数
        let baseTarget = getRandomNumber(4, 6) * itemLen;
        //开奖索引
        let targetIndex = null;
        //基础圈数+开奖索引
        let totalCount = 0;
        //初始化dom渲染
        for (let i = 0; i < itemLen; i++) {
            arr.push("奖项：" + i)
        }
        let domStr = document.createDocumentFragment();
        const domItems = []
        for (let i = 0; i < arr.length; i++) {
            let dom = document.createElement("div");
            dom.className = "item";
            dom.innerHTML = arr[i];

            switch (i) {
                case 0:
                    dom.style.top = 0;
                    dom.style.left = 0;
                    break;
                case 1:
                    dom.style.top = 0;
                    dom.style.left = "110px";
                    break;
                case 2:
                    dom.style.top = 0;
                    dom.style.right = 0;
                    break;
                case 3:
                    dom.style.top = "100px";
                    dom.style.right = 0;
                    break;
                case 4:
                    dom.style.bottom = 0;
                    dom.style.right = 0;
                    break;
                case 5:
                    dom.style.bottom = 0;
                    dom.style.right = "110px";
                    break;
                case 6:
                    dom.style.bottom = 0;
                    dom.style.left = 0;
                    break;
                case 6:
                    dom.style.bottom = "100px";
                    dom.style.left = 0;
                    break;
                case 7:
                    dom.style.bottom = "120px";
                    dom.style.left = 0;
                    break;
            }
            box.appendChild(dom)
            domItems.push(dom);
        }
        box.appendChild(domStr);

        function frame() {

            //清除定时器
            clearTimeout(timer);
            //获取递增过程的索引变量对饮奖项的索引
            let currentpos = startIndex % itemLen;
            //更新奖项的高亮样式
            for (let i = 0; i < itemLen; i++) {
                if (currentpos == i) {
                    domItems[i].classList.add("active");
                }
                else {
                    domItems[i].classList.remove("active");
                }
            }
            //如果达到中奖的目标位置就停止
            if (startIndex == totalCount) {
                clearTimeout(timer);
                return;
            }
            //地址的索引不断的递增
            startIndex++;
            //获取运行比例
            let percent = Math.floor(startIndex / totalCount * 100);
            //递增的索引跑了目标值的50%前都加快
            if (percent <= 50) {
                //需要兜底，否则会出意外
                if (speed > 10) {
                    speed--;
                }
            }
            else {
                //后50%速度开始减速
                speed += 6;
            }
            //这里的定时器的时间是动态的！！！！重要
            timer = setTimeout(() => {
                frame();
            }, speed)
        }
        function startGame() {
            //基础圈数
            baseTarget = getRandomNumber(4, 6) * itemLen;
            //随机目标位置
            targetIndex = getRandomNumber(0, 7);
            //总个数
            totalCount = baseTarget + targetIndex;

            result.innerHTML = "这次开奖的结果：" + arr[targetIndex];
            startIndex = 0;
            //初始化速度
            speed = 80;
            //重置完所有配置后，开始跑定时器
            frame();

        }
        start.onclick = startGame;







    </script>
</body>

</html>