MediaWiki:Common.js

/* Any JavaScript here will be loaded for all users on every page load. */
     const countDownDate = 'January 21 2021 05:00:00 GMT+0000';

    function getTimeRemaining(endtime) {
        const total = Date.parse(endtime) - Date.parse(new Date());
        const seconds = Math.floor((total / 1000) % 60);
        const minutes = Math.floor((total / 1000 / 60) % 60);
        const hours = Math.floor((total / (1000 * 60 * 60)) % 24);
        const days = Math.floor(total / (1000 * 60 * 60 * 24));
        return {
          total: total, 
          days: days, 
          hours: hours,  
          minutes: minutes, 
          seconds: seconds
        };
    }
    function tick(id, endtime) {
      const clock = document.getElementById(id);
      const t = getTimeRemaining(endtime);
      clock.innerHTML = t.days + "d " + t.hours + "h " + t.minutes + "m " + t.seconds + "s ";
            if (t.total <= 0) { clearInterval(timeinterval); }
    }

    function initializeClock(id, endtime) {
        const timeinterval = setInterval(function() { tick(id, endtime) }, 1000);
        tick(id, endtime);
    }

    initializeClock('launch_timer', countDownDate);