setInterval与clearInervar实现秒表功能

<button class="start">开始</button>
  <button class="stop">暂停</button>
  <button class="end">结束</button>
  <h1 class="time">10:9</h1>
  <script>
    let start = document.querySelector('.start')
    let stop = document.querySelector('.stop')
    let end = document.querySelector('.end')
    let time = document.querySelector('.time')
    let seconds = 0
    let ms = 0
    time.innerHTML = `${seconds}:${ms}`
    let timer = null
    // 开启计时器
    start.onclick = function () {
      // 开始的时候删掉之前的计时器并重新开启一个计时器 防止多次开启计时器越来越快的情况
      clearInterval(timer)
      timer = setInterval(() => {
        // 设置进制
        if (ms === 9) {
          seconds++
          ms = 0
        }
        ms++
        time.innerHTML = `${seconds}:${ms}`
      }, 100)
    }
    // 暂停计时器
    stop.onclick = function () {
      clearInterval(timer)
    }
    // 结束计时器
    end.onclick = function () {
      seconds = 0
      ms = 0
      time.innerHTML = `${seconds}:${ms}`
    }
  </script>