Typing of 3 param version of fromEvent in v7 is not compatible with EventEmitter of node.js

[thynson]

Bug Report

Current Behavior
Typing of fromEvent in v7 is not compatible with EventEmitter of node.js, while its declaration claims it's accepted.

Expected behavior
It shall be compatible with v6.

Reproduction

fromEvent(process, 'SIGINT', {once: true}); // Does not compile

Environment

• Runtime: Node v14
• RxJS version: 7

Actually, it's Typescript that does not resolve function overload properly when the function signature contains union type, but at least Typescript is still able to resolve overload by the number of arguments, which is why declaration in v6 works.

[thynson]

Caused by #6214

[cartant]

Needs a minimal reproduction. This seems to be fine, for me with the versions you mentioned:

import { fromEvent } from "rxjs";
const beforeExit = fromEvent(process, "beforeExit");

[thynson]

Sorry, I imported an EventEmitter that is not from 'node' when trying to craft a minimal repo.
But

fromEvent(process, 'SIGINT', {once: true});

does not compile.

[cartant]

AFAICT, this doesn't compile using the Node types:

process.addListener("SIGINT", { once: true });

And the Node documentation makes no mention of an options parameter, so I don't see why we should pass it.

If you were relying on this in v6, I am not at all sure that it would have been doing what you thought it was. This is the v6 implementation and it does not pass options to a Node-style target.

rxjs/src/internal/observable/fromEvent.ts

Lines 221 to 223 in 881cacd

	const source = sourceObj;
	sourceObj.addListener(eventName, handler as NodeEventHandler);
	unsubscribe = () => source.removeListener(eventName, handler as NodeEventHandler);

[thynson]

Umm, the original intent in my codebase was to subscribe to the event for once, so the {once: true} is a misuse and shall be fixed by .pipe(first()).

[thynson]

And the 3-param overload of fromEvent for node's EventEmitter is invalid and shall be removed.