Gadget-countdown.js

function countdown(targetDate, elementId) {

   var countdownDate = new Date(targetDate).getTime();
   var x = setInterval(function() {
       var now = new Date().getTime();
       var distance = countdownDate - now;

       var days = Math.floor(distance / (1000 * 60 * 60 * 24));
       var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
       var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
       var seconds = Math.floor((distance % (1000 * 60)) / 1000);

       document.getElementById(elementId).innerHTML = days + "d " + hours + "h " + minutes + "m " + seconds + "s ";

       if (distance < 0) {
           clearInterval(x);
           document.getElementById(elementId).innerHTML = "EXPIRED";
       }
   }, 1000);

}