js实现随机点名程序

最近用到了一下随机点名程序，就自己整理一下。代码实现后的截图如下。

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>随机点名</title>
  <style>
    #content{
      width: 600px;
      height: 400px;
      background: #000;
      margin: 100px auto;
      text-align: center;
      position: relative;
      line-height: 300px;
      color: dodgerblue;
      font-size: 70px;
    }
    #btn1{
      background: #ccc;
      width: 180px;
      height: 80px;
      font-size: 30px;
      color: #f40;
      border-radius: 12px;
      position: absolute;
      bottom: 30px;
      left: 50%;
      margin-left: -90px;

    }

  </style>
</head>
<body>
  <div id="content">
    <span id="span1">
      点击开始
    </span>
    <button id="btn1">
      start
    </button>

  </div>

  <script>
    var arr = ['中国','英国','德国','美国','意大利','法国','西班牙','日本','阿联酋','荷兰','葡萄牙'];
    var $btn1 = document.getElementById('btn1');
    var $content = document.getElementById('content');
    var $span1 = document.getElementById('span1');
    var timer;//计时器
    var testNum = true;
    $btn1.onclick = function(){
      if(testNum){
        // console.log(1);
        start();
        $btn1.innerHTML = 'stop';
        testNum = false;
      }
      else{
        // console.log(0);
        stop();
        $btn1.innerHTML = 'start';
        testNum = true;
      }
    }
    function start(){
        timer = setInterval(function(){
          var num = random(0,arr.length - 1);
          $span1.innerHTML = arr[num];
        },50)
    }
    function stop(){
        clearInterval(timer);
    }
    // 随机函数
    function random(a,b){
      var randomNum = Math.round(Math.random() * (b - a) + a);
      return randomNum;
    }
  </script>
</body>
</html>

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