javascript - What happens to event listeners when element is removed? - Stack Overflow

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If, for example, I have series of event listeners created like this:

var els = document.getElementyById('myList').getElementsByTagName('li');
for (i=0;i<els.length;i++) {
    els[i].addEventListener(eventType, function(e){ /* do stuff */ }, true);
}

First off, am I mitting some kind of heresy like this? I mean, is there a faaar simpler way of doing this other than an event for each <li> element?

In either case, the main question is: what happens to those event listeners if the <li>s are removed/replaced? What would happen if I did this:

document.getElementyById('myList').innerHTML = 'Hello World!';

Do the listeners stay 'suspended' thus slowing down the browser (assume I have a lot of <li>s), or are they automatically removed? Is it even an issue?

If, for example, I have series of event listeners created like this:

var els = document.getElementyById('myList').getElementsByTagName('li');
for (i=0;i<els.length;i++) {
    els[i].addEventListener(eventType, function(e){ /* do stuff */ }, true);
}

First off, am I mitting some kind of heresy like this? I mean, is there a faaar simpler way of doing this other than an event for each <li> element?

In either case, the main question is: what happens to those event listeners if the <li>s are removed/replaced? What would happen if I did this:

document.getElementyById('myList').innerHTML = 'Hello World!';

Do the listeners stay 'suspended' thus slowing down the browser (assume I have a lot of <li>s), or are they automatically removed? Is it even an issue?

• javascript
• dom-events

Share Improve this question Follow edited Mar 17, 2023 at 21:04 Brian Tompsett - 汤莱恩 5,8937272 gold badges6161 silver badges133133 bronze badges asked Jul 10, 2013 at 13:05 Sean BoneSean Bone 3,55688 gold badges3434 silver badges5050 bronze badges 6

• 3 they are also garbage collected – Arun P Johny Commented Jul 10, 2013 at 13:05
• @ArunPJohny ...meaning? – Sean Bone Commented Jul 10, 2013 at 13:06
• 5 "is there a faaar simpler way of doing this other than an event for each <li> element?" - Using a delegated handler attached to the containing ul element makes sense here. Not necessarily simpler, but only slightly more plicated and more efficient - or maybe it is simpler if you are dynamically adding li elements. And it pletely avoids the issue you are worried about. – nnnnnn Commented Jul 10, 2013 at 13:07
• 2 Meaning they are removed from memory. Also, if every one of your events does the same thing, bind them to the enpassing <ul> - click events will bubble up from the lis to the ul. – Maxim Kumpan Commented Jul 10, 2013 at 13:07
• If the same code is to be executed by the event, you'd want to at least create the function first and then reference it to the eventListener so you don't have multiple identical anonymous functions. – Salketer Commented Jul 10, 2013 at 14:52

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1 Answer 1

Sorted by: Reset to default 13

Event handlers assigned to destroyed elements are marked for garbage collection. Meaning they are removed from memory. Also, if every one of your events does the same thing, bind them to the enpassing <ul> - click events will bubble up from the lis to the ul.

Also,

"is there a faaar simpler way of doing this other than an event for each <li> element?"

Using a delegated handler attached to the containing ul element makes sense here. Not necessarily simpler, but only slightly more plicated and more efficient - or maybe it is simpler if you are dynamically adding li elements. And it pletely avoids the issue you are worried about.

(Courtesy of @nnnnnn)

Converted ment to answer as it seems to have helped answer the question.

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