setInterval() 在 clearInterval() 后不起作用

Question

I am currently making a pomodoro timer in Javascript with start and stop buttons. I'm running into issues with using setInterval() to start the countdown after it has been stopped using clearInterval(). I have 2 functions which are called on click of a button, one starts the countdown using setInterval(), the other stops it using clearInterval(). I'm not sure what's going on, this is my implementation below:

var startTime = 25; // this value will change depending on what the user selects, default value is 25:00
var time = startTime * 60; //number of seconds total
var intervalID; //used for setInterval()

var pomodoroTimer = document.getElementById('pomodoro-timer');


function updateTimer(){
    let minutes = Math.floor(time/60);
    let seconds = time % 60;

    minutes = minutes < 10 ? '0' + minutes : minutes;
    seconds = seconds < 10 ? '0' + seconds : seconds; 

    pomodoroTimer.innerHTML = minutes + ':'+ seconds;
    time--;
}

function startTimer(){
    if(!intervalID){ // to prevent multiple setIntervals being queued up
        updateTimer(); // call this once to stop clock from taking too long on first use of the setInterval function
        intervalID = setInterval(updateTimer, 1000);
    }
}

function stopTimer(){
    clearInterval(intervalID);
}

Answer 1

function stopTimer(){
    clearInterval(intervalID);
    intervalID = undefined;
}