Client side Countdown Timer

How to build global countdown timer using JavaScript

If you are asked to build a countdown timer but you don't have access to server-side language.

"use strict";
var deadline = "Wed, 29 June 2016 18:30:00 GMT-04:00";

function getEndTime(endtime) {
	var t = Date.parse(endtime) - (new Date()).getTime();
	// var end = Date.parse(endtime);
	// var g_current = (new Date().getTime());
	var seconds = Math.floor((t / 1000) % 60);
	var minutes = Math.floor((t / 1000 / 60) % 60);
	var hours = Math.floor((t / (1000 * 60 * 60)) % 24);
	var days = Math.floor(t / (1000 * 60 * 60 * 24));
	return {
		t: t,
		seconds: seconds,
		minutes: minutes,
		hours: hours,
		days: days
	};
}

function countdown(id, endtime) {
	var clock = document.getElementById(id);
	var timeinterval = setInterval(function() {
		var end = getEndTime(endtime);
		var remain = end.t;
		var days = ("0" + end.days).slice(-2);
		var hours = ("0" + end.hours).slice(-2);
		var minutes = ("0" + end.minutes).slice(-2);
		var seconds = ("0" + end.seconds).slice(-2);
		clock.innerHTML = '<table>' +
			'<tr class="days">' +
			'<td colspan="2">' + days + '</td><td>days</td>' +
			'</tr>' +
			'<tr class="hours">' +
			'<td>' + hours + ':</td><td>' + minutes + ':</td><td>' + seconds + '</td>' +
			'</tr>' +
			'<tr class="units">' +
			'<td>hrs</td><td>min</td><td>sec</td>' +
			'</tr>' +
			'</table>';
		if (remain <= 1000) {
			clearInterval(timeinterval);
		}
	}, 1000);
}
countdown('timer', deadline);