Is it necessary/advisable to check if an eventHandler exists before trying to remove it?

Question

I've got something like this:

if (something) {
    init();
} else {
    document.addEventListener('CUSTOM_EVENT', init, false);
}

var init = function() {
    document.removeEventListener('CUSTOM_EVENT', init, false);
    // do stuff
}

Do I need to add some kind of check around that removeEventListener call? If so, I could do:

var eventAdded = false;
if (something) {
    init();
} else {
    document.addEventListener('CUSTOM_EVENT', init, false);
    eventAdded = true;
}

var init = function() {
    if (eventAdded) {
        document.removeEventListener('CUSTOM_EVENT', init, false);
    }
    // do stuff
}

but that feels a bit inelegant. I'd rather just leave the raw removeEventListener call if that's no big deal, or do something that doesn't require having an external var if possible.

James M · Accepted Answer · 2012-03-28 16:48:02Z

16

https://developer.mozilla.org/en/DOM/element.removeEventListener

Calling removeEventListener() with arguments which do not identify any currently registered EventListener on the EventTarget has no effect.

answered Mar 28, 2012 at 16:48

James M

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2 Comments

Andrew Over a year ago

+1 for reference w3.org/TR/DOM-Level-2-Events/…

Jon Over a year ago

This documentation link might be a better first choice for reference (although MDN does say the same, to their credit).

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