JavaScript 倒计时

JavaScript 倒计时是指使用 JavaScript 语言编写的一种实现倒计时功能的代码。这个功能通常用于倒数计时，如网站倒计时广告，定时器等。

以下是一个简单的 JavaScript 倒计时代码：

<p id="demo"></p>

<script>
// Set the date we're counting down to
var countDownDate = new Date("Jan 5, 2023 15:37:25").getTime();

// Update the count down every 1 second
var x = setInterval(function() {

  // Get today's date and time
  var now = new Date().getTime();

  // Find the distance between now and the count down date
  var distance = countDownDate - now;

  // Time calculations for days, hours, minutes and seconds
  var days = Math.floor(distance / (1000 * 60 * 60 * 24));
  var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
  var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
  var seconds = Math.floor((distance % (1000 * 60)) / 1000);

  // Display the result in the element with id="demo"
  document.getElementById("demo").innerHTML = days + "d " + hours + "h "
  + minutes + "m " + seconds + "s ";

  // If the count down is finished, write some text
  if (distance < 0) {
    clearInterval(x);
    document.getElementById("demo").innerHTML = "EXPIRED";
  }
}, 1000);
</script>

这段代码实现了一个倒数计时器，每一秒更新一次倒计时信息。当倒计时结束时，代码会在页面上显示“EXPIRED”。