Tampermonkey Vacation Countdown

gistfile1.js

// ==UserScript==
// @name         Vacation Countdown
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  GTFO Counter!
// @author       You
// @match        *://*/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

function getTimeRemaining(endtime) {
  var t = Date.parse(endtime) - Date.parse(new Date());
  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 {
    'total': t,
    'days': days,
    'hours': hours,
    'minutes': minutes,
    'seconds': seconds
  };
}

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

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

    daysSpan.innerHTML = t.days;
    hoursSpan.innerHTML = ('0' + t.hours).slice(-2);
    minutesSpan.innerHTML = ('0' + t.minutes).slice(-2);
    secondsSpan.innerHTML = ('0' + t.seconds).slice(-2);

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

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



var b = document.createElement("div");
b.innerHTML = '<div id="clockdiv"><h3><center><span class="days"></span> Days ,<span class="hours"></span> Hours, <span class="minutes"></span> Minutes, <span class="seconds"></span> Seconds till Vacation</center></h3></div>';
document.body.insertBefore(b, document.body.firstChild);

var deadline = new Date(2016,9,8,0,0,0,0);
initializeClock('clockdiv', deadline);

})();