Timer continues after 0

I made a timer for a project in school (I am still in school yes and I do not have JavaScript as a lesson that we get this semester) in JavaScript and it continues after the 0. I got some help from a teacher but I can’t reach him with the pandemic and stuff.

This is the code that I wrote and what happens is that when it reaches the date that I put in it goes into -0 -0 -0 -01 and continues from there.

const countdown = () => {
    let countDate = new Date('Febuary 9, 2022 00:00:00').getTime();
    let now = new Date().getTime();
    let gap = countDate - now;

    let second = 1000;
    let minute = second * 60;
    let hour = minute * 60;
    let day = hour * 24;

    let textDay = Math.floor(gap / day);
    let textHour = Math.floor((gap % day) / hour);
    let textMinute = Math.floor((gap % hour) / minute);
    let textSecond = Math.floor((gap % minute) / second);

    document.querySelector('.day').innerText = textDay;
    document.querySelector('.hour').innerText = textHour;
    document.querySelector('.minute').innerText = textMinute;
    document.querySelector('.second').innerText = textSecond;

};

setInterval(countdown, 1000);

>Solution :

setInterval returns a value which you can pass to clearInterval to stop the interval from running. Store that value in a variable, for example:

let countInterval = 0;

const countdown = () => {
  //...
};

countInterval = setInterval(countdown, 1000);

Then within countdown you can check if you want to clear that interval. For example, if you want to clear it when gap <= 0 you would perform that logic:

if (gap <= 0) {
  clearInterval(countInterval);
  return;
}

This would stop the interval from running when that condition is eventually met.

Example:

let countInterval = 0;

const countdown = () => {
    let countDate = new Date('January 11, 2022 13:35:00').getTime();
    let now = new Date().getTime();
    let gap = countDate - now;
    
    if (gap <= 0) {
      clearInterval(countInterval);
      return;
    }

    let second = 1000;
    let minute = second * 60;
    let hour = minute * 60;
    let day = hour * 24;

    let textDay = Math.floor(gap / day);
    let textHour = Math.floor((gap % day) / hour);
    let textMinute = Math.floor((gap % hour) / minute);
    let textSecond = Math.floor((gap % minute) / second);

    document.querySelector('.day').innerText = textDay;
    document.querySelector('.hour').innerText = textHour;
    document.querySelector('.minute').innerText = textMinute;
    document.querySelector('.second').innerText = textSecond;

};

countInterval = setInterval(countdown, 1000);

<div class="day"></div>
<div class="hour"></div>
<div class="minute"></div>
<div class="second"></div>