Allow EventListener to be removed within its own handler

[mikesol]

I'm wondering if it'd be possible to have some sort of Lazy instantiation of EventListener? It's often the case that I call removeEventListener in the body of an event listener, which requires having a handle to the event listener.

Conceptually laziness seems to be safe, as I don't think an EventListener can be called during the same tick as its creation without some unsafeCoerce-ery. At the same time, I'm not quite sure how to implement that API wise. I'm pretty sure there's a language extension that accomplishes this in Haskell (when you have a left-binded expression that refers to its own variable name) but I forget the name.

[garyb]

Perhaps the simplest way of resolving this would be to include a pre-fix'ed version of eventListener? I added something similar for Refs.

I've used AVars in the past to get a reference to the listener into itself, but that's a lot of machinery (since it also only works in Aff - could also be done with Refs, but that introduces partiality that needs handling, even though it failing is "impossible") for something that could be easily solved with a bit of FFI.

[mikesol]

I didn't know about AVar - that does the trick for me for now! I don't mind the extra machinery personally. Maybe leave this open and if anyone else complains we can revisit?

[JordanMartinez]

I think this issue can be renamed to something like "Allow EventListener to be removed within its own handler"