events: getEventListeners static #35991

benjamingr · 2020-11-06T10:10:53Z

This adds a static getEventListeners to events. The major difference between it and .listeners is that it works with EventTargets and not just EventEmitters.

This is useful after talking to users of EventTarget and AbortController for two main reasons:

For diagnostics and digging into why EventTargets are behaving and trying to isolate possible memory leaks.
For creating linked AbortSignals potentially.

cc @bterlson

This has to be a static because we are not allowed to add this method on EventTarget.prototype. I checked with WHATWG and the only way I could come up with that is both spec compliant and addresses the use case.

The web platform itself does not have a way to do this (due to encapsulation) but I double checked we are allowed to expose this functionality as long as it's not on EventTarget itself (from the public #whatwg IRC channel):

Checklist

make -j4 test (UNIX), or vcbuild test (Windows) passes
tests and/or benchmarks are included
documentation is changed or added
commit message follows commit guidelines

addaleax · 2020-11-06T10:11:56Z

doc/api/events.md

+For `EventEmitter`s this behaves exactly the same as calling `.listeners` on
+the emitter.
+
+For `EventTargegt`s this is the only way to get the event listeners for the


Suggested change

For `EventTargegt`s this is the only way to get the event listeners for the

For `EventTarget`s this is the only way to get the event listeners for the

aduh95

It seems unlikely this will be backported to v12 (going to maintenance this month), so we may as well use optional chaining

lib/events.js

nodejs-github-bot · 2020-11-06T10:42:32Z

CI: https://ci.nodejs.org/job/node-test-pull-request/34121/

nodejs-github-bot · 2020-11-07T09:10:27Z

CI: https://ci.nodejs.org/job/node-test-pull-request/34158/

aduh95 · 2020-11-07T10:23:49Z

test/parallel/test-events-static-geteventlisteners.js

@@ -0,0 +1,37 @@
+// Flags: --expose-internals --no-warnings


That seems unnecessary:

Suggested change

// Flags: --expose-internals --no-warnings

This is needed for NodeEventTarget no?

Oh, I ended up not needing it, fun

nodejs-github-bot · 2020-11-08T11:48:59Z

CI: https://ci.nodejs.org/job/node-test-pull-request/34194/

doc/api/events.md

Trott · 2020-11-08T13:30:18Z

doc/api/events.md

@@ -829,6 +829,39 @@ class MyClass extends EventEmitter {
 }
 ```

+### `events.getEventListeners(emitterOrTarget, eventName)`


Suggested change

### `events.getEventListeners(emitterOrTarget, eventName)`

## `events.getEventListeners(emitterOrTarget, eventName)`

nodejs-github-bot · 2020-11-08T13:52:50Z

CI: https://ci.nodejs.org/job/node-test-pull-request/34205/

benjamingr · 2020-11-08T16:43:00Z

@addaleax @Trott @mcollina any chance this can get a second LGTM to not wait a week :]?

github-actions · 2020-11-09T07:39:36Z

Landed in ad98cf0...1a6d4dc

PR-URL: #35991 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Notable changes: * events: getEventListeners static (Benjamin Gruenbaum) (#35991) * fs: add support for AbortSignal in readFile (Benjamin Gruenbaum) (#35911) PR URL: #36055

Notable changes: * events: * getEventListeners static (Benjamin Gruenbaum) (#35991) * fs: * support abortsignal in writeFile (Benjamin Gruenbaum) (#35993) * add support for AbortSignal in readFile (Benjamin Gruenbaum) (#35911) * stream: * fix thrown object reference (Gil Pedersen) (#36065) PR URL: #36055

sperez841

PR-URL: nodejs#35991 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

PR-URL: #35991 Backport-PR-URL: #38386 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Use `getEventListeners` instead of `listenerCount` because nodejs#35991 was landed. Refs: nodejs#35991 Refs: nodejs#36006

Use `getEventListeners` instead of `listenerCount` because #35991 was landed. Refs: #35991 Refs: #36006 PR-URL: #47759 Reviewed-By: Daeyeon Jeong <daeyeon.dev@gmail.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Mestery <mestery@protonmail.com>

Use `getEventListeners` instead of `listenerCount` because nodejs#35991 was landed. Refs: nodejs#35991 Refs: nodejs#36006 PR-URL: nodejs#47759 Reviewed-By: Daeyeon Jeong <daeyeon.dev@gmail.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Mestery <mestery@protonmail.com>

benjamingr added events Issues and PRs related to the events subsystem / EventEmitter. semver-minor PRs that contain new features and should be released in the next minor version. labels Nov 6, 2020

benjamingr requested review from mcollina, jasnell and addaleax November 6, 2020 10:10

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bterlson mentioned this pull request Nov 6, 2020

Warn on EventTarget maxListeners > THRESHOLD #35990

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events: add max listener warning for EventTarget #36001

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events: getEventListeners static

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events: getEventListeners static

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PR-URL: #35991 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

todo bot mentioned this pull request Nov 9, 2020

[pull] master from nodejs:master daddyfatstacksBIG/node#973

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events: getEventListeners static

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PR-URL: #35991 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

danielleadams mentioned this pull request Nov 9, 2020

v15.2.0 proposal #36055

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danielleadams added a commit that referenced this pull request Nov 9, 2020

2020-11-10, Version 15.2.0 (Current)

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Notable changes: * events: getEventListeners static (Benjamin Gruenbaum) (#35991) * fs: add support for AbortSignal in readFile (Benjamin Gruenbaum) (#35911) PR URL: #36055

danielleadams added a commit that referenced this pull request Nov 10, 2020

2020-11-10, Version 15.2.0 (Current)

5d9154f

Notable changes: * events: getEventListeners static (Benjamin Gruenbaum) (#35991) * fs: add support for AbortSignal in readFile (Benjamin Gruenbaum) (#35911) PR URL: #36055

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[pull] master from nodejs:master daddyfatstacksBIG/node#1193

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events: getEventListeners static

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PR-URL: nodejs#35991 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

targos mentioned this pull request Apr 24, 2021

[v14.x] Backport AbortController and friends #38386

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targos pushed a commit to targos/node that referenced this pull request Apr 26, 2021

events: getEventListeners static

b02e11c

PR-URL: nodejs#35991 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

targos pushed a commit to targos/node that referenced this pull request Apr 30, 2021

events: getEventListeners static

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PR-URL: nodejs#35991 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

targos pushed a commit that referenced this pull request Apr 30, 2021

events: getEventListeners static

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PR-URL: #35991 Backport-PR-URL: #38386 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

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v14.17.0 proposal #38507

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deokjinkim added a commit to deokjinkim/node that referenced this pull request Apr 28, 2023

test: refactor to use getEventListeners in timers

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Use `getEventListeners` instead of `listenerCount` because nodejs#35991 was landed. Refs: nodejs#35991 Refs: nodejs#36006

deokjinkim mentioned this pull request Apr 28, 2023

test: refactor to use getEventListeners in timers #47759

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events: getEventListeners static #35991

events: getEventListeners static #35991

benjamingr commented Nov 6, 2020

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sperez841 left a comment

	For `EventTargegt`s this is the only way to get the event listeners for the
	For `EventTarget`s this is the only way to get the event listeners for the

	### `events.getEventListeners(emitterOrTarget, eventName)`
	## `events.getEventListeners(emitterOrTarget, eventName)`

events: getEventListeners static #35991

events: getEventListeners static #35991

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