JS小時倒計時

let t1 = new Date("2019-11-26 15:51:00");// 從什么時間開始
let t2 = new Date(t1.setHours(t1.getHours() + 1));// 延遲幾個小時
let interval = window.setInterval(() => {
  let t3 = t2 - new Date();// 延遲時間距離當前時間的時間戳 if (t3 <= 0) {
    alert("時間到！");
    window.clearInterval(interval);
    return;
  }
  let leave1 = t3 % (24 * 3600 * 1000);// 獲取毫秒數
  let hours = Math.floor(leave1 / (3600 * 1000));// 獲取小時數
  let leave2 = leave1 % (3600 * 1000);// 排除小時的毫秒數
  let minutes = Math.floor(leave2 / (60 * 1000));// 獲取分鍾
  let leave3 = leave2 % (60 * 1000);// 排除分鍾的毫秒數
  let seconds = Math.round(leave3 / 1000);// 獲取秒
  window.console.log((hours > 9 ? hours : "0" + hours) + ":" + (minutes > 9 ? minutes : "0" + minutes) + ":" + (seconds > 9 ? seconds : "0" + seconds));
}, 500);