<div class="wrapper">
    <div>謝謝惠顧</div>
    <div>十萬元現金</div>
    <div>謝謝惠顧</div>
    <div>iphone11</div>
    <div>抽獎</div>
    <div>美的冰箱</div>
    <div>謝謝惠顧</div>
    <div>50元紅包</div>
    <div>謝謝惠顧</div>
  </div>
<div class="result"></div>

<style>
    .wrapper {
      width: 300px;
      height: 300px;
      display: flex;
      flex-flow: row wrap;
      position: absolute;
      top: 0;
      left: 0;
      right: 0;
      bottom: 0;
      margin: auto;
      border: 1px solid red;
    }
    
    .wrapper div {
      flex: none;
      width: 100px;
      height: 100px;
      box-sizing: border-box;
      border: 1px solid red;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    
    .active {
      background-color: red;
    }
    
    .wrapper div:nth-child(5) {
      cursor: pointer;
    }
    
    .result {
      height: 100px;
      display: inline-block;
      position: absolute;
      top: 50px;
      left: 0;
      right: 0;
      margin: auto;
      text-align: center;
      line-height: 100px;
      font-size: 40px;
      font-weight: 700;
      color: #ff4400;
    }
</style>

<script>
    var t, m, num, time, index, target, current;
    //以索引值為0，1，2，5，8，7，6，3的div元素為循環目標，
    //因為以num總數遞減的方式進行循環，故將數組倒序定義
    var arr = [3, 6, 7, 8, 5, 2, 1, 0];
    var div = document.querySelectorAll('.wrapper div');
    var result = document.querySelector('.result');
    div[4].onclick = function() {
      clearInterval(time);
      div[4].innerHTML = '抽獎中...';
      result.innerHTML = '';
      //中獎目標設為0到7的隨機整數
      target = Math.floor(Math.random() * 8);
      //起始位置設為隨機，且以num為總的循環數
      num = Math.floor(Math.random() * 8) + 40;
      //將總循環數的2/3保存，方便調整速率峰值出現的時間
      //若m為總循環的1/2，則速度峰值會在總時長的中間出現
      m = Math.floor(num * 2 / 3);
      //此處if語句可限制中獎，從第一個開始外圈順時針分別對應7，6，5，4，3，2，1，0
      //如設置target == 6 即限制中十萬元現金，以下代碼為100%不中獎
      if (target == 6|| target == 4 || target == 2 || target == 0) { 
         target++;
       }
      speed();

      function speed() {
        //將循環目標div的索引值轉換為循環總數的表達式
        index = arr[num % 8];
        //給當前循環元素添加樣式，并移除之前的樣式
        if (current) {
          current.remove('active');
        }
        div[index].classList.add('active');
        current = div[index].classList;
        //速度函數，可調試速率
        t = Math.floor(Math.pow((num - m), 2) + 250);
        //一次性定時器，嵌套遞歸循環控制速度
        time = setTimeout(function() {
            speed()
          }, t)
        //判斷中獎結果
        if (num == target) {
          clearTimeout(time);
          div[4].innerHTML = '抽獎';
          switch (target) {
            case 6:
              result.innerHTML = '恭喜您抽中' + div[arr[target % 8]].innerHTML + '大獎';
              break;
            case 4:
              result.innerHTML = '恭喜您抽中' + div[arr[target % 8]].innerHTML;
              break;
            case 2:
              result.innerHTML = '恭喜您抽中' + div[arr[target % 8]].innerHTML;
              break;
            case 0:
              result.innerHTML = '恭喜您抽中' + div[arr[target % 8]].innerHTML;
              break;
            default:
              result.innerHTML = div[arr[target % 8]].innerHTML;
          }
        }
        num--;
      }
    }


</script>