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EventDispatcher: remove unwanted references in event objects. #18564

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Mar 27, 2021
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EventDispatcher: remove unwanted references in event objects. #18564

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2 changes: 2 additions & 0 deletions src/core/EventDispatcher.js
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Expand Up @@ -76,6 +76,8 @@ Object.assign( EventDispatcher.prototype, {

}

event.target = null;
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Um, I'm not sure it's a good idea to alter the event object after it was dispatched. Users could work with the event object not just within the event listener. They could save the event and work with it later on. In this case it would be unexpected when target is suddenly null.

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I see your point, although anyone being called knows what target is (this), in the listener functions. Is target used anywhere within Three? I can't see any obvious uses.

An alternative would be to zap it specifically in the Object3D.remove() method after the dispatch call. In those cases anyone saving the event object could get surprises anyway since it would be shared with other _removed events after that point.

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I was thinking the same thing but if that's the case any reused event definitions like this would be problematic because target will get overwritten with every subsequent call. TrackballControls, TransformControls, OrbitControls and I'm sure others all use this same pattern.

These events were originally moved to be reused in order to save on memory allocation (see #17224, #17134 (comment)) but I missed that the object was modified in the dispatchEvent function. I personally am okay with denoting that an event is only valid during the execution of the callback, which would allow us to save memory allocation in quite a few other places.

Setting the target to null in the dispatchEvent function would change the functionality relative to the built relative to the EventTarget.dispatchEvent function, though, so it might be more sensible to set target to null in the remove() function, instead.

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@Mugen87 Mugen87 Feb 7, 2020 •
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I've totally forgot that three.js code already reuses event objects...

In this case, I prefer whatever @mrdoob likes. Also note that this class comes from a separate github repo. It could be useful to make changes also there: https://github.com/mrdoob/eventdispatcher.js/


}

}
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