How to stop JavaScript Timer?

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>

In order to use clearInterval, you have to assign setInterval to a variable and then use that variable as a pararmeter to clearInterval. You can probably use the answer at stackoverflow.com/questions/16599878/… — Doug F
– Doug F, Commented Mar 1, 2019 at 22:13
setInterval() returns an id for the created and running interval. You need to store it on a variable if you want to clear ir later. Then you can call clearInterval(<some_id>);. — Shidersz
– Shidersz, Commented Mar 1, 2019 at 22:13

aristarinsv · Accepted Answer · 2019-03-01 22:25:54Z

2

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);
    };
    ...

answered Mar 1, 2019 at 22:25

aristarinsv

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Comments

Adam Chubbuck · Accepted Answer · 2019-03-01 22:17:26Z

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>

Vladimir Ivanov · Accepted Answer · 2019-03-01 22:17:51Z

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.

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