Куда уменьшается переменная timeLeft?

var timeLeft = 60;
const elem = document.getElementById('timer');

countdown(); // To prevent the timer from starting after a 1 second pause
const timerId = setInterval(countdown, 1000);

function countdown() {
    if (timeLeft == -1) {
        clearTimeout(timerId); // To stop the timer
    } else {
        elem.innerHTML = timeLeft;
        timeLeft--;
    }

    seconds = 60 - timeLeft; // The time taken to complete the quiz

    if (timeLeft == -1) { // If the timer runs out, all elements will disappear, and ONLY the score will be displayed
        outline.style.display = 'none';
        square.style.display = 'none';
        title.style.display = 'none';
        quizTimer.style.display = 'none';
        displayResult.style.display = '';
        displayResult.textContent = 'Score = ' + score;
    }
}