events.once creates an error listener that is not removed on abort.

[draivin]

• Version: v15.5.0
• Platform: Microsoft Windows NT 10.0.20279.0 x64
• Subsystem:

What steps will reproduce the bug?

let events = require('events');

let ac = new AbortController();
let e = new events.EventEmitter();

events.once(e, 'test', {signal: ac.signal});

ac.abort();

console.log(e.listeners('test'));
console.log(e.listeners('error'));

How often does it reproduce? Is there a required condition?

Always.

What is the expected behavior?

The error listener should be removed, so console.log should print an empty array.

What do you see instead?

console.log prints an array with one listener.

Additional information

It seems the wrong listener is being removed in the following line:

node/lib/events.js

Line 739 in eb8422c

eventTargetAgnosticRemoveListener(emitter, 'error', resolver);

The error listener is called errorListener, not resolver.

[ronag]

@benjamingr

[benjamingr]

Good catch!

[benjamingr]

I'll note that it's frustrating that we support the signal option for addEventListener but not for on/once (due to performance considerations) - using that instead of removeEventListener with a reference would have made this sort of bug a lot less likely.