Expose setMaxListeners property on AbortSignal

What is the problem this feature will solve?

Right now, there is no stable way to change the maxEventTargetListeners of an AbortSignal without importing from node:events.

This makes it impossible to write isomorphic library code that adds more than the default 10 event listeners, without having to resort to workarounds such as

/**
 * A workaround to set the `maxListeners` property of a node EventEmitter without having to import
 * the `node:events` module, which would make the code non-portable.
 */
function setMaxListeners(maxListeners: number, emitter: any) {
  const key = Object.getOwnPropertySymbols(new AbortController().signal).find(
    (key) => key.description === "events.maxEventTargetListeners"
  );
  if (key) emitter[key] = maxListeners;
}

This relies on the events.maxEventTargetListeners symbol description, which, to my knowledge is not part of any public API and could change at any time.

What is the feature you are proposing to solve the problem?

Add a AbortSignal.setMaxListeners instance method so isomorphic code could do something like

if ('setMaxListeners' in signal) signal.setMaxListeners(20)

What alternatives have you considered?

Alternatively, if this is not an option as it could pollute a spec-defined object with additional properties, use Symbol.for instead of new Symbol for kMaxEventTargetListeners and make that a part of the official api.

I would be willing to implement this feature.

The right avenue to purse this change is WHATWG (the group maintaining those standards). From past experience, any time we deviate from the standard we cause more harm than good.

But isn't maxEventTargetListeners in itself - a limit on the number of listeners and issuing a warning - already a node-only deviation from the standard?

So this would try to explore a way to get closer to the standard, not further away.

By that logic, another alternative suggestion here could be:

Alternative suggestion: set no default listener count limit on `AbortController`

On all newly created AbortSignal instances, set the kMaxEventTargetListeners to 0 by default to align with standard behaviour - users that want a limit on event listeners can still use setMaxListeners to set a specific limit.

In the research before opening this ticket, I've seen a lot of instances where people were getting this warning with undici fetch, so this seems to be a somewhat common problem.

In my case, this is ironically caused because I want to pass an AbortSignal as the signal option to a lot of addEventListener calls so I can make sure to clean them up.

Either way, it seems that AbortSignal is just made to be reused by many fetch calls or addEventListener calls, so the current limit of 10 is easily reached by normal intended usage (and afaik not to spec).

@jasnell

@jasnell you added the warning in
#36001

@KhafraDev you added those getters/setters in
#47039

What do you folks think?

node shouldn't have implemented warnings or interop with EventEmitter in the first place, but we absolutely shouldn't deviate further from the spec and other implementations

@nodejs/web-standards what do you all think?

@lucacasonato

Pinging @lucacasonato too (hope you don't mind).

@KhafraDev

Agree with @KhafraDev. If anything this should be a setter function you import from node:events that you pass the signal to as the first argument.

I agree. We should not extend the standard API with non-standard extensions.

+1 (no nonstandard extensions). I do like the alternative suggestion tho (#54758 (comment))

I agree with the alternative suggestion as well

@phryneas

@phryneas I think that library is simple to create, as I think most bundlers allow for browsers alternates, so that some code will execute in Node.js but never in the browsers, making it isomorphic.

So we've gone from a library with a single (and rather short) published code file to a library with 3 published code files (2 environment-specific ones, one shared), an exports field with nested conditions and a sophisticated build setup.

I might as well publish this on npm as isomorphic-abortsignal in the end, to not bloat the original library and enable others to use it without going through the same pain.

Honestly, this feels wrong - and I'm sorry that I voice my frustration here, but I feel like it needs to be said.

This is not how things should end up when node starts picking up web standards - the need for these workarounds should go down, not up :(

@phryneas

@phryneas even if we removed the warning, this will hardly trickle down to past releases. I'm not even sure we should make it semver-minor or not.

Anyhow, would you like to send a PR to remove the warning limit? I don't see much opposition in keeping it.

@phryneas

@phryneas even if we removed the warning, this will hardly trickle down to past releases. I'm not even sure we should make it semver-minor or not.

That's still a lot better than doing nothing :)

Anyhow, would you like to send a PR to remove the warning limit? I don't see much opposition in keeping it.

Will do!

lib: disable default memory leak warning for AbortSignal

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Solved for my use case via #55816

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Expose `setMaxListeners` property on `AbortSignal` #54758

What is the problem this feature will solve?

What is the feature you are proposing to solve the problem?

What alternatives have you considered?

Alternative suggestion: set no default listener count limit on `AbortController`

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Expose setMaxListeners property on AbortSignal #54758

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What is the problem this feature will solve?

What is the feature you are proposing to solve the problem?

What alternatives have you considered?

Activity

mcollina commented on Sep 4, 2024

phryneas commented on Sep 4, 2024

phryneas commented on Sep 4, 2024

Alternative suggestion: set no default listener count limit on AbortController

mcollina commented on Sep 4, 2024

KhafraDev commented on Sep 4, 2024

mcollina commented on Sep 4, 2024

mcollina commented on Sep 4, 2024

lucacasonato commented on Sep 4, 2024

jasnell commented on Sep 4, 2024

ljharb commented on Sep 4, 2024

benjamingr commented on Sep 4, 2024

7 remaining items

mcollina commented on Nov 10, 2024

phryneas commented on Nov 10, 2024

mcollina commented on Nov 11, 2024

phryneas commented on Nov 11, 2024

github-actions commented on May 11, 2025

phryneas commented on May 11, 2025

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Expose `setMaxListeners` property on `AbortSignal` #54758

Alternative suggestion: set no default listener count limit on `AbortController`