<body>
    <button>发送</button>
  </body>
  <script>
    var btn = document.querySelector("button");
    var time = 3; //定义剩下的秒数
    btn.addEventListener("click", function () {
      btn.disabled = true;
      var timer = setInterval(function () {
        if (time == 0) {
          // 清除定时器和复原按钮
          clearInterval(timer);
          btn.disabled = false;
          btn.innerHTML = "发送";
          time = 3;
        } else {
          btn.innerHTML = "还剩下" + time + "秒";
          time--;
        }
      }, 1000);
    });
  </script>