Javascript incluido la data de Blogger para contador regresivo

contador-regresivo.js

//<![CDATA[
'use strict';
var getRemainingTime = function getRemainingTime(deadline) {
  var now = new Date(),
      remainTime = (new Date(deadline) - now + 1000) / 1000,
      remainSeconds = ('0' + Math.floor(remainTime % 60)).slice(-2),
      remainMinutes = ('0' + Math.floor(remainTime / 60 % 60)).slice(-2),
      remainHours = ('0' + Math.floor(remainTime / 3600 % 24)).slice(-2),
      remainDays = Math.floor(remainTime / (3600 * 24));

  return {
    remainSeconds: remainSeconds,
    remainMinutes: remainMinutes,
    remainHours: remainHours,
    remainDays: remainDays,
    remainTime: remainTime
  };
};

var countdown = function countdown(deadline, elem, finalMessage) {
  var el = document.getElementById(elem);

  var timerUpdate = setInterval(function () {
    var t = getRemainingTime(deadline);
    el.innerHTML = '<span class="counter-clock__item">' + t.remainDays + 'd</span><span class="counter-clock__item">' + t.remainHours + 'h</span><span class="counter-clock__item">' + t.remainMinutes + 'm</span><span class="counter-clock__item">' + t.remainSeconds + 's</span>';

    if (t.remainTime <= 1) {
      clearInterval(timerUpdate);
      el.innerHTML = '<p class="counter-clock__info">' + finalMessage + '</p>';
    }
  }, 1000);
};
//]]>
countdown('<b:eval expr='data:items[1]'/> <b:eval expr='data:items[2]'/>', 'counter-clock', '<b:eval expr='data:items[3]'/>');