countdown.js

 // Set the date we're counting down to
 var countDownDate = new Date("Oct 31, 2020 23:59:59").getTime();

 // Update the count down every 1 second
 var x = setInterval(function () {
   // Get today's date and time
   var now = new Date().getTime();

   // Find the distance between now and the count down date
   var distance = countDownDate - now;

   // Time calculations for days, hours, minutes and seconds
   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);

   // Output the result in an element with id="demo"
   document.getElementById("demo").innerHTML =
     "<b>" +
     days +
     "</b>" +
     "d " +
     "<b>" +
     hours +
     "</b>" +
     "h " +
     "<b>" +
     minutes +
     "</b>" +
     "m " +
     "<b>" +
     seconds +
     "</b>" +
     "s ";

   // If the count down is over, write some text
   if (distance < 0) {
     clearInterval(x);
     document.getElementById("demo").innerHTML = "EXPIRED";
   }
 }, 1000);