JSFiddle - React, Tailwind, and code Playground

HTML

<div id="countdown"></div>

CSS

body {
  padding: 50px;
  font: 14px "Lucida Grande", Helvetica, Arial, sans-serif;
}

a {
  color: #00B7FF;
}

JavaScript

CountDownTimer('October 21, 2015 19:00:00', 'countdown');

function CountDownTimer(date, id) {
    var end       = new Date(date);
    
    var _second   = 1000;
    var _minute   = _second * 60;
    var _hour     = _minute * 60;
    var _day      = _hour * 24;
    var timer;
    
    var showRemaining = function() {
        var now = new Date();
        var distance = end - now;

        if (distance < 0) {   
            clearInterval(timer);
            document.getElementById(id).innerHTML = 'EXPIRED!';
            return;
        }

        var days = Math.floor(distance / _day);
        var hours = Math.floor((distance % _day) / _hour);
        var minutes = Math.floor((distance % _hour) / _minute);
        var seconds = Math.floor((distance % _minute) / _second);
        
        document.getElementById(id).innerHTML =  days + ' days ';
        document.getElementById(id).innerHTML += hours + ' hours ';
        document.getElementById(id).innerHTML += minutes + ' mins ';
        document.getElementById(id).innerHTML += seconds + ' secs';
    };
    
    timer = setInterval(showRemaining, 1000);
}