JSFiddle - React, Tailwind, and code Playground

HTML

<div id="counter-container">
      <div class="counter-box">
        <div class="counter"><p id="d" class="counter-p">#</p></div>
        <p class="counter-box-p">days</p>
      </div>
      <div class="counter-box">
        <div class="counter"><p id="h" class="counter-p">#</p></div>
        <p class="counter-box-p">hours</p>
      </div>
      <div class="counter-box">
        <div class="counter"><p id="m" class="counter-p">#</p></div>
        <p class="counter-box-p">minutes</p>
      </div>
      <div class="counter-box">
        <div class="counter"><p id="s" class="counter-p">#</p></div>
        <p class="counter-box-p">seconds</p>
      </div>

JavaScript

function counter(futureDate) {
  var today = new Date(); // today
  count = Math.floor((futureDate-today)/1000);
  countdown = setInterval(function(){
    var temp;
    $("p#d").html(Math.floor(count/(60*60*24)));
    temp = count%(60*60*24);
    $("p#h").html(Math.floor(temp/(60*60)));
    temp = count%(60*60);
    $("p#m").html(Math.floor(temp/(60)));
    temp = count%(60);
    $("p#s").html(temp);
    if (count == 0) {
         alert("time's up");
         clearInterval(countdown);       
    }
    count--;
  }, 1000);
}

counter(new Date(2012,4,8)); // May 8, 2012 00:00:00
/* counter(new Date(2012,4,8,15,49,10)); // May 8, 2012 15:49:00 */