指定时间，倒计时效果

<div id="countdown"></div>
<script type="text/javascript">
    function startCountdown(targetDate, display) {
      var timer = setInterval(function () {
        var currentDate = new Date();
        var timeDiff = targetDate.getTime() - currentDate.getTime();

        if (timeDiff <= 0) {
          clearInterval(timer);
          display.textContent = "已过期";
          return;
          }

        //var days = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
        var hours = Math.floor((timeDiff / (1000 * 60 * 60)) % 24);
        var minutes = Math.floor((timeDiff / (1000 * 60)) % 60);
        var seconds = Math.floor((timeDiff / 1000) % 60);

        var countdownStr = hours + "小时 " + minutes + "分钟 " + seconds + "秒";
        display.textContent = countdownStr;

      }, 1000);
    }

var countdown = document.getElementById("countdown");
var targetDate = new Date("2023-04-20T08:56:50+08:00"); // 指定要倒计时的目标时间
startCountdown(targetDate, countdown);
</script>