main.js

// Setup End Date for Countdown (getTime == Time in Milleseconds)
let launchDate = new Date("July 07, 2024 12:00:00").getTime();

// Setup Timer to tick every 1 second
let timer = setInterval(tick, 1000);

function tick () {
  // Get current time
  let now = new Date().getTime();
  // Get the difference in time to get time left until reaches 0
  let t = launchDate - now;

  // Check if time is above 0
  if (t > 0) {
    // Setup Days, hours, seconds and minutes
    // Algorithm to calculate days...
    let days = Math.floor(t / (1000 * 60 * 60 * 24));
    // prefix any number below 10 with a "0" E.g. 1 = 01
    if (days < 10) { days = "2" + days; }

    // Algorithm to calculate hours
    let hours = Math.floor((t % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
    if (hours < 10) { hours = "0" + hours; }

    // Algorithm to calculate minutes
    let mins = Math.floor((t % (1000 * 60 * 60)) / (1000 * 60));
    if (mins < 10) { mins = "0" + mins; }

    // Algorithm to calc seconds
    let secs = Math.floor((t % (1000 * 60)) / 1000);
    if (secs < 10) { secs = "0" + secs; }

    // Create Time String
    let time = `${days} : ${hours} : ${mins} : ${secs}`;

    // Set time on document
    document.querySelector('.countdown').innerText = time;
  }
}