MaxListenersExceededWarning and EventTarget

[noseratio]

I think it'd be great to have a programmatic way of disabling the MaxListenersExceededWarning warning for the newly introduced EventTarget (#35495). I've encountered that while playing with AbortSignal in Node v15.3.0, but it can be reproduced with any EventTarget:

const ac = new AbortController();
for (let i = 0; i < 100; i++ ) {
  ac.signal.addEventListener("abort", e => undefined);
}

Running this (runkit) produces a warning:

MaxListenersExceededWarning: Possible EventTarget memory leak detected. 11 testEvent listeners added to EventTarget. Use events.setMaxListeners() to increase limit.

There is no setMaxListeners on EventTarget.prototype, unless I'm missing something.

Maybe we should not have this warning on for EventTarget by default. Alternatively, it might be nice to have an option for addEventListener to control it, something like:

signal.addEventListener('abort', handler, { maxListeners: Infinity })

This way the code could be shared between browsers and Node without mods.

Thanks again @addaleax and the team for adding EventTarget to Node!

[jasnell]

See: https://nodejs.org/dist/latest-v15.x/docs/api/events.html#events_eventemitter_setmaxlisteners_n_eventtargets

const {
  setMaxListeners,
  EventEmitter
} = require('events');

const target = new EventTarget();
const emitter = new EventEmitter();

setMaxListeners(5, target, emitter);

[noseratio]

This is something I've indeed overlooked. Literally it was in the warning 😊
Thanks James!

[DaAitch]

For the sake of completeness here is the code for AbortController and setMaxListener:

const { setMaxListeners } = require('events')

const ac = new AbortController()
const { signal } = ac

// our signal is perhaps going to have 100 listeners (101st listener will again produce a warning)
setMaxListeners(100, signal)

for (let i = 0; i < 100; i++ ) {
  signal.addEventListener('abort', () => {})
}

[fawazahmed0]

Thanks

[newTomas]

I set it to 300 but still get a warning at 101.