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events: getEventListeners static #35991

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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):

Screen Shot 2020-11-05 at 21 02 17

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

@benjamingr 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
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
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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

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

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

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

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This is needed for NodeEventTarget no?

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Oh, I ended up not needing it, fun

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

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

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

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github-actions bot commented Nov 9, 2020

Landed in ad98cf0...1a6d4dc

@github-actions github-actions bot closed this Nov 9, 2020
nodejs-github-bot pushed a commit that referenced this pull request Nov 9, 2020
PR-URL: #35991
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
danielleadams pushed a commit that referenced this pull request Nov 9, 2020
PR-URL: #35991
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
@danielleadams danielleadams mentioned this pull request Nov 9, 2020
danielleadams added a commit that referenced this pull request Nov 9, 2020
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
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
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
danielleadams added a commit that referenced this pull request Nov 10, 2020
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
danielleadams added a commit that referenced this pull request Nov 10, 2020
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
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targos pushed a commit to targos/node that referenced this pull request Apr 24, 2021
PR-URL: nodejs#35991
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
targos pushed a commit to targos/node that referenced this pull request Apr 26, 2021
PR-URL: nodejs#35991
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
targos pushed a commit to targos/node that referenced this pull request Apr 30, 2021
PR-URL: nodejs#35991
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
targos pushed a commit that referenced this pull request Apr 30, 2021
PR-URL: #35991
Backport-PR-URL: #38386
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
@danielleadams danielleadams mentioned this pull request May 3, 2021
deokjinkim added a commit to deokjinkim/node that referenced this pull request Apr 28, 2023
Use `getEventListeners` instead of `listenerCount` because nodejs#35991
was landed.

Refs: nodejs#35991
Refs: nodejs#36006
nodejs-github-bot pushed a commit that referenced this pull request May 3, 2023
Use `getEventListeners` instead of `listenerCount` because #35991
was landed.

Refs: #35991
Refs: #36006
PR-URL: #47759
Reviewed-By: Daeyeon Jeong <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Mestery <[email protected]>
targos pushed a commit that referenced this pull request May 3, 2023
Use `getEventListeners` instead of `listenerCount` because #35991
was landed.

Refs: #35991
Refs: #36006
PR-URL: #47759
Reviewed-By: Daeyeon Jeong <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Mestery <[email protected]>
targos pushed a commit that referenced this pull request May 3, 2023
Use `getEventListeners` instead of `listenerCount` because #35991
was landed.

Refs: #35991
Refs: #36006
PR-URL: #47759
Reviewed-By: Daeyeon Jeong <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Mestery <[email protected]>
danielleadams pushed a commit that referenced this pull request Jul 6, 2023
Use `getEventListeners` instead of `listenerCount` because #35991
was landed.

Refs: #35991
Refs: #36006
PR-URL: #47759
Reviewed-By: Daeyeon Jeong <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Mestery <[email protected]>
MoLow pushed a commit to MoLow/node that referenced this pull request Jul 6, 2023
Use `getEventListeners` instead of `listenerCount` because nodejs#35991
was landed.

Refs: nodejs#35991
Refs: nodejs#36006
PR-URL: nodejs#47759
Reviewed-By: Daeyeon Jeong <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Mestery <[email protected]>
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