JSFiddle - React, Tailwind, and code Playground

by mrienstra

HTML

<!--h1>Countdown Clock</h1-->
<div id="clockdiv">
  <div>
    <span class="days"></span>
    <div class="smalltext">Days</div>
  </div>
  <div>
    <span class="hours"></span>
    <div class="smalltext">Hours</div>
  </div>
  <div>
    <span class="minutes"></span>
    <div class="smalltext">Minutes</div>
  </div>
  <div>
    <span class="seconds"></span>
    <div class="smalltext">Seconds</div>
  </div>
  <div>
    <span class="all_seconds"></span>
    <div class="smalltext">All Seconds</div>
  </div>
</div>

CSS

html{
  height: 100%;
}
body{
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100%;
	text-align: center;
	background: #000;
  font-family: sans-serif;
  font-weight: 100;
}

h1{
  color: #396;
  font-weight: 100;
  font-size: 40px;
  margin: 40px 0px 20px;
}

#clockdiv{
  display: inline-block;
	font-family: sans-serif;
	color: #aaa;
	font-weight: 100;
	text-align: center;
	font-size: 30px;
}

#clockdiv > div{
  margin: 10px;
	padding: 10px;
	border-radius: 3px;
	background: #222;
	display: inline-block;
}

#clockdiv div > span{
	padding: 15px;
	border-radius: 3px;
	background: #111;
	display: inline-block;
}

.smalltext{
	padding-top: 5px;
	font-size: 16px;
  color: #444;
}

JavaScript

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,
    days,
    hours,
    minutes,
    seconds
  };
}

function initializeClock(id, endtime) {
  const clock = document.getElementById(id);
  const daysSpan = clock.querySelector('.days');
  const hoursSpan = clock.querySelector('.hours');
  const minutesSpan = clock.querySelector('.minutes');
  const secondsSpan = clock.querySelector('.seconds');
  const allSecondsSpan = clock.querySelector('.all_seconds');

  function updateClock() {
    const t = getTimeRemaining(endtime);

    daysSpan.innerHTML = -1 * t.days;
    hoursSpan.innerHTML = ('0' + t.hours).slice(-2);
    minutesSpan.innerHTML = ('0' + t.minutes).slice(-2);
    secondsSpan.innerHTML = ('0' + t.seconds).slice(-2);
    allSecondsSpan.innerHTML = (Math.abs(t.total) / 1000).toLocaleString();

    if (t.total <= 0) {
      clearInterval(timeinterval);
    }
  }

  updateClock();
  const timeinterval = setInterval(updateClock, 1000);
}

const deadline = new Date(Date.parse("January 1, 2021 00:00:00 PST"));
initializeClock('clockdiv', deadline);