how to run a countdown timer in javascript code example

Example 1: countdown in javascript

<!DOCTYPE html>
<html lang="en">
   <head>
      <meta charset="UTF-8" />
      <title>Countdown timer using HTML and JavaScript</title>
   </head>
   <body>
      Registration closes in <span id="timer">05:00<span> minutes!

      <!-- custom js -->
      <script>
         window.onload = function () {
            var minute = 5;
            var sec = 60;
            setInterval(function () {
               document.getElementById("timer").innerHTML =
                  minute + " : " + sec;
               sec--;
               if (sec == 00) {
                  minute--;
                  sec = 60;
                  if (minute == 0) {
                     minute = 5;
                  }
               }
            }, 1000);
         };
      </script>
   </body>
</html>

Example 2: countdown in js

function startTimer(duration, display) {
    var timer = duration, minutes, seconds;
    setInterval(function () {
        minutes = parseInt(timer / 60, 10);
        seconds = parseInt(timer % 60, 10);

        minutes = minutes < 10 ? "0" + minutes : minutes;
        seconds = seconds < 10 ? "0" + seconds : seconds;

        display.textContent = minutes + ":" + seconds;

        if (--timer < 0) {
            timer = duration;
        }
    }, 1000);
}

window.onload = function () {
    var fiveMinutes = 60 * 5,
        display = document.querySelector('#time');
    startTimer(fiveMinutes, display);
};