Simple Countdown Timer

<div id="countdown"></div>

<script>

        function countdownTimer() {

            var endTime = new Date("December 31, 2025 23:59:59").getTime();

            var now = new Date().getTime();

            var timeLeft = endTime - now;

            var days = Math.floor(timeLeft / (1000 * 60 * 60 * 24));

            var hours = Math.floor((timeLeft % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));

            var minutes = Math.floor((timeLeft % (1000 * 60 * 60)) / (1000 * 60));

            var seconds = Math.floor((timeLeft % (1000 * 60)) / 1000);

            document.getElementById('countdown').innerHTML = days + "d " + hours + "h " +

                minutes + "m " + seconds + "s ";

            if (timeLeft < 0) {

                clearInterval(x);

                document.getElementById('countdown').innerHTML = "EXPIRED";

            }

        }

        setInterval(function() { countdownTimer(); }, 1000);

</script>