clearInterval() not working [duplicate]

Asked 2/2, 2013 at 21:53 Answered 3/2, 2013 at 0:53

Solved javascript scope setinterval clearinterval

Possible Duplicate:
JS - How to clear interval after using setInterval()

I have a function that changes the font-family of some text every 500 ms using setInterval (I made it just to practice JavaScript.) The function is called by clicking on an "on" button and the interval is supposed to be cleared using a separate button, "off". However, the "off" button doesn't actually clear the interval, it just continues. I suspect that this has something to do with scope but I'm not sure how to write it any other way. Also, I don't want to do this with jQuery because, after all, I'm doing it to learn.

<body>
<p><span id="go" class="georgia">go</span> Italian</p>
<p>
    <button id="on" type="button" value="turn on">turn on</button>
    <button id="off" type="button" value="turn off">turn off</button>
</p>

<script>
var text = document.getElementById("go");
var on = document.getElementById("on");
var off = document.getElementById("off");

var fontChange = function() {
    switch(text.className) {
        case "georgia":
            text.className = "arial";
            break;
        case "arial":
            text.className = "courierNew";
            break;
        case "courierNew":
            text.className = "georgia";
            break;      
    }
};

on.onclick = function() {
    setInterval(fontChange, 500);
};

off.onclick = function() {
    clearInterval(fontChange);
}; 
</script>
</body>

Facia answered 2/2, 2013 at 21:53 Comment(2)

I did look at the MDN spec first but it didn't help me with the problem. – Facia 3/2, 2013 at 0:35

window.timer = setInterval(fontChange, 500); clearInterval(window.timer) – Assyrian 25/2, 2018 at 12:8

setInterval returns an ID which you then use to clear the interval.

var intervalId;
on.onclick = function() {
    if (intervalId) {
        clearInterval(intervalId);
    }
    intervalId = setInterval(fontChange, 500);
};

off.onclick = function() {
    clearInterval(intervalId);
};

Burundi answered 2/2, 2013 at 21:56 Comment(1)

this is fine, but you'll run into another problem if you are using setInterval() (or setTimeout()) in a situation where it's possible to run it multiple time. If you'll click twice, you'll never clear the first setInterval(). You either need if(intervalId !== undefined) { intervalId = setInterval(... or make intervalId an Array if you want more setIntervals on each additional click – Hauptmann 10/1, 2017 at 1:49

The setInterval function returns an integer value, which is the id of the "timer instance" that you've created.

It is this integer value that you need to pass to clearInterval

e.g:

var timerID = setInterval(fontChange,500);

and later

clearInterval(timerID);

Monogenic answered 2/2, 2013 at 21:56 Comment(0)

i think you should do:

var myInterval
on.onclick = function() {
    myInterval=setInterval(fontChange, 500);
};

off.onclick = function() {
    clearInterval(myInterval);
};

Dick answered 2/2, 2013 at 21:57 Comment(0)

You're using clearInterval incorrectly.

This is the proper use:

Set the timer with

var_name = setInterval(fontChange, 500);

and then

clearInterval(var_name);

Benford answered 2/2, 2013 at 21:58 Comment(0)

The setInterval method returns an interval ID that you need to pass to clearInterval in order to clear the interval. You're passing a function, which won't work. Here's an example of a working setInterval/clearInterval

var interval_id = setInterval(myMethod,500);
clearInterval(interval_id);

Beguile answered 2/2, 2013 at 21:56 Comment(0)

There are errors in your functions, but the first thing you should do, is to set the body tag correctly:

<body>
<p><span id="go" class="georgia">go</span> Italian</p>
<p>
    <button id="on" type="button" value="turn on">turn on</button>
    <button id="off" type="button" value="turn off">turn off</button>
</p>
</body>

<script>....</script>

The problem sometimes may be, that you call 'var text' and the other vars only once, when the script starts. If you make changements to the DOM, this static solution may be harmful.

So you could try this (this is more flexible approach and using function parameters, so you can call the functions on any element):

<body>
<p><span id="go" class="georgia">go</span> Italian</p>
<p>
    <button type="button" value="turn on"
         onclick=turnOn("go")>turn on</button>
    <button type="button" value="turn off"
         onclick=turnOff()>turn off</button>
</p>
</body>

<script type="text/JavaScript">
var interval;

var turnOn = function(elementId){
    interval = setInterval(function(){fontChange(elementId);}, 500);
};

var turnOff = function(){
    clearInterval(interval);
};

var fontChange = function(elementId) {
    var text = document.getElementById(elementId);
    switch(text.className) {
        case "georgia":
            text.className = "arial";
            break;
        case "arial":
            text.className = "courierNew";
            break;
        case "courierNew":
            text.className = "georgia";
            break;      
    }
};
</script>

You don't need this anymore, so delete it:

var text = document.getElementById("go");
var on = document.getElementById("on");
var off = document.getElementById("off");

This is dynamic code, meaning JS code which runs generic and doesn't adress elements directly. I like this approach more than defining an own function for every div element. ;)

Kabuki answered 3/2, 2013 at 0:53 Comment(0)

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