JS制作簡單的倒計時功能

<script>
 (function () {

 var tian = document.getElementsByClassName('JS-tian')[0];
 var shi = document.getElementsByClassName('JS-shi')[0];
 var fen = document.getElementsByClassName('JS-fen')[0];
 var miao = document.getElementsByClassName('JS-miao')[0];

 var endTime = new Date('2117/07/12 23:59:59').getTime() + 1000;

 var interval = null;
 interval = setInterval(function () {
 var syhm = endTime - Date.now(); // 剩余毫秒
 if (syhm >= 0) {
 tian.innerText = Math.floor(syhm / 1000 / 60 / 60 / 24);
 shi.innerText = Math.floor(syhm / 1000 / 60 / 60 % 24);
 fen.innerText = Math.floor(syhm / 1000 / 60 % 60);
 miao.innerText = Math.floor(syhm / 1000 % 60);
 } else {
 clearInterval(interval);
 }
 }, 0);

 })();
</script>

<div>
 距結束還剩：<span class="JS-tian"></span>天<span class="JS-shi"></span>時<span class="JS-fen"></span>分<span class="JS-miao"></span>秒
</div>