A simple JavaScript countdown timer

clock.js

(function () {
  dayjs.extend(window.dayjs_plugin_duration);

  const launchDay = Date.parse("2022-06-10T21:00:00Z");

  const daysOutput = document.getElementById("countdown-days");
  const hoursOutput = document.getElementById("countdown-hours");
  const minutesOutput = document.getElementById("countdown-minutes");
  const secondsOutput = document.getElementById("countdown-seconds");

  let duration;

  setInterval(() => {
    duration = dayjs.duration(launchDay - Date.now());
    daysOutput.textContent = duration["$d"].days;
    hoursOutput.textContent =
      duration["$d"].hours > 9
        ? duration["$d"].hours
        : `0${duration["$d"].hours}`;
    minutesOutput.textContent =
      duration["$d"].minutes > 0
        ? duration["$d"].minutes
        : `0${duration["$d"].minutes}`;
    secondsOutput.textContent =
      duration["$d"].seconds > 9
        ? duration["$d"].seconds
        : `0${duration["$d"].seconds}`;
  }, 100);
})();