Timer

const days = document.getElementById("days");
const hours = document.getElementById("hours");
const minutes = document.getElementById("minutes");
const seconds = document.getElementById("seconds");
const input = document.getElementById("date");
const show = document.getElementById("show");
let intervalId

const getCurrentDate = (from, to) => {
  return {
    remainingDays: Math.floor((from - to) / 1000 / 60 / 60 / 24),
    remainingHours: Math.floor((from - to) / 1000 / 60 / 60 % 24),
    remainingMinutes: Math.floor((from - to) / 1000 / 60 % 60),
    remainingSeconds: Math.floor((from - to) / 1000 % 60),
  }
}

const render = (date) => {
  const {
    remainingDays,
    remainingHours,
    remainingMinutes,
    remainingSeconds,
  } = date

  days.textContent = remainingDays +" д "
  hours.textContent = remainingHours +" ч "
  minutes.textContent = remainingMinutes +" м "
  seconds.textContent = remainingSeconds +" с "
}

const timer = (from) => {
    const to = Date.now()

    render(getCurrentDate(from, to))

    if (!intervalId) {
     intervalId = setInterval(() => timer(from), 1000);
    }

    if(
      Object.values(getCurrentDate(from, to)).every(param => !param)
    ) {
        clearInterval(intervalId)
    }
}

const countdownTimer = () => {
    const target = new Date(input.value)

    timer(target)
}

input.addEventListener("keydown", (e) => {
    if(e.keyCode < 48 || e.keyCode > 57) {
        e.preventDefault();
    }
    let len = input.value.length
    if(len == 4) {

        input.value = input.value + "."
    }
    if(len == 7) {
        input.value = input.value + "."
    }
    if(len == 10) {
        input.value = input.value + " / "
    }
    if(len == 15) {
        input.value = input.value + ":"
    }
    if(len == 18) {
        e.preventDefault();
    }
});

show.addEventListener("click", countdownTimer)