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Add async emit methods to EventEmitter #18646

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Add async emit methods to EventEmitter#18646
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eventsIssues and PRs related to EventEmitter and the events module.feature requestIssues requesting new Node.js features.

Description

@matthewadams
matthewadams
opened on Feb 8, 2018

  • Version:
    v8.9.4

  • Platform:
    Darwin pumba-5.local 17.4.0 Darwin Kernel Version 17.4.0: Sun Dec 17 09:19:54 PST 2017; root:xnu-4570.41.2~1/RELEASE_X86_64 x86_64

  • Subsystem:
    events

https://nodejs.org/api/events.html#events_asynchronous_vs_synchronous instructs users to cause asynchronous event execution in the event handlers by using setImmediate or process.nextTick, which means that, when using EventEmitter#emit, asynchronous event handling is left to clients, and the EventEmitter has no control over whether an event is handled asynchronously or synchronously. In cases where the EventEmitter is sensitive to performance, the EventEmitter itself can dictate the event emission is asynchronous via code similar to the following:

class MyClass extends EventEmitter {
  // ...
  doSomething() {
    process.nextTick(() => this.emit.bind(this).call('myEvent', {foo:'bar'}))
    // ...
  }
}

The emit line above could be replaced by something convenient like

this.emitNextTick('myEvent', {foo:'bar'})
// or
this.emitImmediate('myEvent', {foo:'bar'})

or, even more conveniently,

this.emitAsync('myEvent', {foo:'bar'})

which uses either setImmediate or process.nextTick according to the current environment.

Activity

  1. bnoordhuis
    added
    eventsIssues and PRs related to EventEmitter and the events module.
    feature requestIssues requesting new Node.js features.
    on Feb 15, 2018

  2. bnoordhuis commented on Feb 15, 2018

    @bnoordhuis
    bnoordhuis
    on Feb 15, 2018
    Member

    Asynchronous emit has been discussed as early as 2010 or 2011. It never happened and I wouldn't expect it to happen now. Ultimately (and as you mention), it's a convenience, not a necessity.

  3. apapirovski commented on Apr 14, 2018

    @apapirovski
    apapirovski
    on Apr 14, 2018
    Contributor

    There doesn't seem to be much movement or interest in this feature so I'll close this out but feel free to re-open if you feel strongly about including this in core and/or plan to work on a PR. I tend to agree that it's a convenience that can be easily implemented either in a user-land module or even on a per project basis (it's a 1 liner).

  4. apapirovski
    closed this as completedon Apr 14, 2018

  5. macedd commented on Mar 13, 2019

    @macedd
    macedd
    on Mar 13, 2019

    This is how I solved the async emitter https://github.com/thiagof/async-event-emitter

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