清除定时器clearInterval：

<body>
    <button class="kai">开启定时器</button>
    <button class="guan">关闭定时器</button>
  </body>
  <script>
    var begin = document.querySelector(".kai ");
    var stop = document.querySelector(".guan ");
    var att = null;
    begin.addEventListener("click", function () {
      att = setInterval(function () {
        console.log("我很好");
      }, 1000);
    });
    stop.addEventListener("click", function () {
      clearInterval(att);
    });
  </script>