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[v12.x] events: assume an EventEmitter if emitter.on is a function #35818

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[v12.x] events: assume an EventEmitter if emitter.on is a function #35818

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lpinca
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@lpinca lpinca commented Oct 26, 2020

Assume that the emitter argument of EventEmitter.once() is an
EventEmitter if emitter.on is a function.

Refs: 4b3654e923e7c3c2
Refs: websockets/ws#1795

Checklist
  • make -j4 test (UNIX), or vcbuild test (Windows) passes
  • tests and/or benchmarks are included
  • commit message follows commit guidelines

@lpinca
events: assume an EventEmitter if emitter.on is a function
32067a6 
Assume that the `emitter` argument of `EventEmitter.once()` is an
`EventEmitter` if `emitter.on` is a function.

Refs: nodejs@4b3654e923e7c3c2
Refs: websockets/ws#1795
@nodejs-github-bot nodejs-github-bot added events Issues and PRs related to the events subsystem / EventEmitter. v12.x labels Oct 26, 2020
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lpinca commented Oct 26, 2020 •
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This fixes a breaking change introduced in 9150c4dc72.

The EventTarget implementation is still experimental so I don't think
#33556 and all the PRs linked in #33556 (comment) will be packported to v12.x

@lpinca lpinca changed the title events: assume an EventEmitter if emitter.on is a function [v12.x] events: assume an EventEmitter if emitter.on is a function Oct 26, 2020
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@lpinca note that that PR was added in order to support EventTarget in userland, Node's own EventTarget isn't actually directly exposed to user-land (outside AbortController).

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I don't think this use case (of something that behaves like both eventemitter and eventtarget) is common and a quick GitHub search doesn't find interesting results.

I am fine with landing this change as semver-patch.

Preferring EventTarget makes sense to me - the only thing that might break is NodeEventTarget but that looks fine to me.

The biggest difference here is error handling (adding the error event handler to the EventEmitter).

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Also fwiw I am fine with this change in master (and not just 12.x)

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lpinca commented Oct 26, 2020 •
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On master, v15.x, and v14.x it's already like this. See linked refs.

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@lpinca Ah lmao, I am the author of that and absolutely forgot about that 😅

@MylesBorins MylesBorins added the request-ci Add this label to start a Jenkins CI on a PR. label Nov 3, 2020
@github-actions github-actions bot removed the request-ci Add this label to start a Jenkins CI on a PR. label Nov 3, 2020
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@lpinca lpinca mentioned this pull request Nov 4, 2020
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CI: https://ci.nodejs.org/job/node-test-pull-request/34049/

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@nodejs/events can we please get one more sign off on this

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pinging @nodejs/events can we please get another sign-off here?

maybe @mcollina ?

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mcollina approved these changes Nov 16, 2020
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lgtm

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Landed in a211c70e04aa

MylesBorins pushed a commit that referenced this pull request Nov 16, 2020
@lpinca @MylesBorins
events: assume an EventEmitter if emitter.on is a function
b484732 
Assume that the `emitter` argument of `EventEmitter.once()` is an
`EventEmitter` if `emitter.on` is a function.

Refs: 4b3654e923e7c3c2
Refs: websockets/ws#1795

PR-URL: #35818
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
@lpinca lpinca deleted the fix/events-once branch November 16, 2020 19:20
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@mcollina mcollina mcollina approved these changes

@benjamingr benjamingr benjamingr approved these changes

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