如何停止 JavaScript 计时器？

Question

I have a simple Bootstrap page that includes a 45 second countdown timer and a button which I intend to include on a bigger project later. The countdown timer will start on a click of the button.

What I wanted to do is that when I click on the button again within the 45 seconds countdown interval, the counter will reset. I am not able to do that. What I tried to do is to use the clearInterval function at the very beginning of the errorTimer function. But, it did not work.

Here are my codes:

 // Timer for error message - 45 seconds. function startTimer(duration, display) { var timer = duration, minutes, seconds; setInterval(function() { minutes = parseInt(timer / 60, 10) seconds = parseInt(timer % 60, 10); minutes = minutes < 10 ? "0" + minutes : minutes; seconds = seconds < 10 ? "0" + seconds : seconds; display.textContent = minutes + ":" + seconds; if (--timer < 0) { timer = duration; } }, 1000); } function errorTimer() { var fortyFiveSeconds = 60 * .75, display = document.querySelector('#time'); startTimer(fortyFiveSeconds, display); };

 <link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.2.1/css/bootstrap.min.css" rel="stylesheet" /> <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.2.1/js/bootstrap.min.js"></script> <div class="container-fluid"> <div class="row"> <div class="col-md-12 mt-5">&nbsp;</div> </div> <div class="row"> <div class="col-md-4"></div> <div class="col-md-4 text-center"> <p id="time"></p> </div> <div class="col-md-4"></div> </div> </div> <button type="button" class="btn btn-info" onclick="errorTimer()">Submit Button</button>

Answer 1

Use clearInterval like this

...
    // Timer for error message - 45 seconds.    
    var timerId;
    function startTimer(duration, display) {
    var timer = duration, minutes, seconds;
    if(timerId != undefined) {
        clearInterval(timerId)
    }
    timerId = setInterval(function () {
        minutes = parseInt(timer / 60, 10)
        seconds = parseInt(timer % 60, 10);

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

        display.textContent = minutes + ":" + seconds;
        if (--timer < 0) {
            timer = duration;
        }
    }, 1000);
    }

    function errorTimer () {
        var fortyFiveSeconds = 60 * .75,
        display = document.querySelector('#time');
    startTimer(fortyFiveSeconds, display);
    };
    ...

Answer 2

As @Shidersz mentioned, you need to store the id associated with the interval and use that id to clear the interval before resetting the clock.

 // Timer for error message - 45 seconds. var id = null; function startTimer(duration, display) { if (id !== null) { clearInterval(id); id = null; } var timer = duration, minutes, seconds; id = setInterval(function() { minutes = parseInt(timer / 60, 10) seconds = parseInt(timer % 60, 10); minutes = minutes < 10 ? "0" + minutes : minutes; seconds = seconds < 10 ? "0" + seconds : seconds; display.textContent = minutes + ":" + seconds; if (--timer < 0) { timer = duration; } }, 1000); } function errorTimer() { var fortyFiveSeconds = 60 * .75, display = document.querySelector('#time'); startTimer(fortyFiveSeconds, display); };

 <link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.2.1/css/bootstrap.min.css" rel="stylesheet" /> <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.2.1/js/bootstrap.min.js"></script> <div class="container-fluid"> <div class="row"> <div class="col-md-12 mt-5">&nbsp;</div> </div> <div class="row"> <div class="col-md-4"></div> <div class="col-md-4 text-center"> <p id="time"></p> </div> <div class="col-md-4"></div> </div> </div> <button type="button" class="btn btn-info" onclick="errorTimer()">Submit Button</button>

Answer 3

You could stop the timer by clearing the interval:

// Timer for error message - 45 seconds.    
function startTimer(duration, display) {
var timer = duration, minutes, seconds;
var interval = setInterval(function () {
    minutes = parseInt(timer / 60, 10)
    seconds = parseInt(timer % 60, 10);

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

    display.textContent = minutes + ":" + seconds;
    if (--timer < 0) {
        timer = duration;
    }
}, 1000);
    return function(){ clearInterval(interval); };
}

function errorTimer () {
    var fortyFiveSeconds = 60 * .75,
    var display = document.querySelector('#time');
    var stopper = startTimer(fortyFiveSeconds, display);
    setTimeout(stopper, 20 * 1000); // stop timer 20 seconds later.
};

---

I make use of a simple function returned by the startTimer function, that can be used to clear the interval at a later point.