countDownTimer.js

// program to create a countdown timer

// time to countdown from (in milliseconds)
let countDownDate = new Date().getTime() + 24 * 60 * 60 * 1000;

// countdown timer
let x = setInterval(function() {

    // get today's date and time in milliseconds
    let now = new Date().getTime();

    // find the interval between now and the countdown time
    let timeLeft = countDownDate - now;

    // time calculations for days, hours, minutes and seconds
    const days = Math.floor( timeLeft/(1000*60*60*24) );
    const hours = Math.floor( (timeLeft/(1000*60*60)) % 24 );
    const minutes = Math.floor( (timeLeft/1000/60) % 60 );
    const seconds = Math.floor( (timeLeft/1000) % 60 );

    // display the result in the element with id="demo"
    console.log(days + "d " + hours + "h " + minutes + "m " + seconds + "s ");

    // clearing countdown when complete
    if (timeLeft < 0) {
        clearInterval(x);
        console.log('CountDown Finished');
    }
    }, 2000);