前端计数器：实时显示小时分钟秒-优快云博客

本文链接：https://blog.youkuaiyun.com/Asmruan/article/details/121940238

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      header {
        height: 500px;
        width: 400px;
        background-color: cyan;
        margin: auto;
        text-align: center;
        padding-top: 40px;
      }
      button {
        margin: 10px;
      }
    </style>
  </head>
  <body>
    <header>
      <div>
        <span>00 </span>
        <span>00 </span>
        <span>00 </span>
      </div>
      <div><button>开始</button></div>
      <div><button>暂停</button></div>
      <div><button>归零</button></div>
    </header>
  </body>
</html>
<script>
  function add0(num) {
    return num >= 10 ? num : "0" + num;
  }

  var start = document.querySelectorAll("button")[0];
  var pause = document.querySelectorAll("button")[1];
  var stop = document.querySelectorAll("button")[2];
  var h = document.querySelectorAll("span")[0];
  var m = document.querySelectorAll("span")[1];
  var s = document.querySelectorAll("span")[2];

  var num = 0;
  var timer = null;
  start.addEventListener("click", function () {
    timer = setInterval(function () {
      num++;
      s.innerHTML = add0(num);
      // 小时向下取整
      var hour = add0(Math.floor(num / 60 / 60));
      //   66  1分零6秒
      // 1小时 = 60*60 = 3600s
      //   3666   1小时1分6秒
      // 62
      var minutes = add0(Math.floor(num / 60) % 60);
      var second = add0(num % 60);
      h.innerHTML = hour;
      m.innerHTML = minutes;
      s.innerHTML = second;
    }, 0);
  });
</script>