Countdown Timer with JS

countdown.js

// JavaScript Countdown Timer

let endDate = new Date("Dec 25, 2020 00:00:00").getTime();

const timer = setInterval(tick, 1000)

function tick () {
    let currentTime = new Date().getTime();
    let timeLeft = endDate - currentTime;

    if (timeLeft > 0) {
        
        // Calculate Days
        let daysLeft = Math.floor(timeLeft / (1000*60*60*24));
        if (daysLeft < 10){
            daysLeft = "0" + daysLeft; 
        }

        // Calculate Hrs
        let hoursLeft = Math.floor((timeLeft % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
        if (hoursLeft < 10){
            hoursLeft = "0" + hoursLeft; 
        }

        // Calculate Mins
        let minLeft = Math.floor((timeLeft % (1000 * 60 * 60)) / (1000 * 60));
        if (minLeft < 10){
            minLeft = "0" + minLeft; 
        }

        // Calculate Secs
        let secLeft = Math.floor((timeLeft % (1000 * 60)) / 1000);
        if (secLeft < 10){
            secLeft = "0" + secLeft; 
        }

        // TIME STRING for display
        
        let displayTime = `Christmas countdown ${daysLeft} days  ${hoursLeft} hrs  ${minLeft} mins ${secLeft} secs `;

        document.querySelector('.countdown').innerText = displayTime;
    }
}

// create a <div> with className="countdown" for result to display