Type signature review progress for v7 beta

[cartant]

This issue is for the tracking of the review of the TypeScript signatures - that involve either an Observable or ObservableInput rest parameter or a callback that returns ObservableInput or have open, type-related issues, etc. - as per the discussion in today's core-team meeting.

Deprecations for the scheduler-related changes are not in this list. My understanding is that those deprecations will remain in place, with the breaking changes being made in version 8.

@benlesh As I've review individual source files, I'll check them off in this list if they're okay and will link to a comment (or issue) if changes are required or attention is warranted.

In addition to what's shown below, I think we should look at how null and undefined are used to ensure that passing either- to indicate the absence of an argument - is supported.

• AsyncSubject.ts
• BehaviorSubject.ts
• Notification.ts - see fix: fix up notification types #5478, use more exact return type in Notification#do #5031
• Observable.ts - see Observable does not implement InteropObservable #3890, Refine subscribe and tap signatures #4159, RxJS incorrectly defines observable symbol #4415 and fix(toPromise): correct toPromise return type #5072
• Observer.ts
• Operator.ts
• ReplaySubject.ts
• Scheduler.ts
• Subject.ts - see this comment
• Subscriber.ts
• Subscription.ts
• types.ts - see from is typed to accept any Subscribable, but only accepts Observables with Symbol.observable #4532 and this comment and this comment
• observable/bindCallback.ts - needs N-args signature for values? Should fall back to unknown instead of any. Also, see this comment.
• observable/bindNodeCallback.ts - needs N-args signature for values? Should fall back to unknown instead of any. Also, see this comment.
• observable/combineLatest.ts - needs N-args signature for observable inputs? See also forkJoin should emit empty array or object given empty array or object as input #5209
• observable/concat.ts
• observable/defer.ts
• observable/dom/AjaxObservable.ts
• observable/dom/WebSocketSubject.ts
• observable/dom/ajax.ts
• observable/dom/animationFrames.ts
• observable/dom/fetch.ts - see fromFetch cannot abort all responses #4744
• observable/dom/webSocket.ts
• observable/empty.ts
• observable/forkJoin.ts - needs N-args signature for observable inputs? See also forkJoin should emit empty array or object given empty array or object as input #5209
• observable/from.ts - see from is typed to accept any Subscribable, but only accepts Observables with Symbol.observable #4532
• observable/generate.ts
• observable/iif.ts
• observable/interval.ts
• observable/merge.ts - needs N-args signature for observable inputs?
• observable/never.ts
• observable/of.ts - see Update of.ts #5027
• observable/onErrorResumeNext.ts - needs N-args signature for observable inputs?
• observable/pairs.ts - see pairs observable static function does not infers correctly #4468
• observable/partition.ts
• observable/race.ts - needs N-args signature for observable inputs?
• observable/range.ts
• observable/throwError.ts
• observable/timer.ts
• observable/using.ts - needs observable input factory handled?
• observable/zip.ts - needs N-args signature for observable inputs? Also see forkJoin should emit empty array or object given empty array or object as input #5209
• operators/audit.ts
• operators/auditTime.ts
• operators/buffer.ts
• operators/bufferCount.ts
• operators/bufferTime.ts
• operators/bufferToggle.ts
• operators/bufferWhen.ts
• operators/catchError.ts
• operators/combineAll.ts
• operators/combineLatest.ts - see Rename all operators that are duplicates of static operators to xWith variants #3927 and needs N-args signature for observable inputs?
• operators/concat.ts - see Rename all operators that are duplicates of static operators to xWith variants #3927 and needs N-args signature for observable inputs?
• operators/concatAll.ts
• operators/concatMap.ts
• operators/concatMapTo.ts
• operators/count.ts
• operators/debounce.ts
• operators/debounceTime.ts
• operators/defaultIfEmpty.ts
• operators/delay.ts
• operators/delayWhen.ts
• operators/dematerialize.ts (more work here fix: fix up notification types #5478)
• operators/distinct.ts
• operators/distinctUntilChanged.ts
• operators/distinctUntilKeyChanged.ts
• operators/elementAt.ts
• operators/endWith.ts - needs N-args signature for values?
• operators/every.ts
• operators/exhaust.ts
• operators/exhaustMap.ts
• operators/expand.ts - needs observable input factory handled?
• operators/filter.ts
• operators/finalize.ts
• operators/find.ts
• operators/findIndex.ts
• operators/first.ts
• operators/groupBy.ts
• operators/ignoreElements.ts
• operators/isEmpty.ts
• operators/last.ts
• operators/map.ts
• operators/mapTo.ts - see Amendment to mapTo operator type #5090
• operators/materialize.ts
• operators/max.ts
• operators/merge.ts - see Rename all operators that are duplicates of static operators to xWith variants #3927 and needs N-args signature for observable inputs?
• operators/mergeAll.ts
• operators/mergeMap.ts
• operators/mergeMapTo.ts
• operators/mergeScan.ts
• operators/min.ts
• operators/multicast.ts
• operators/observeOn.ts
• operators/onErrorResumeNext.ts - needs N-args signature for observable inputs?
• operators/pairwise.ts
• operators/pluck.ts
• operators/publish.ts
• operators/publishBehavior.ts - see Add selector to publishBehavior #2845
• operators/publishLast.ts
• operators/publishReplay.ts - see Add selector to publishBehavior #2845
• operators/race.ts - see Rename all operators that are duplicates of static operators to xWith variants #3927 and needs N-args signature for observable inputs?
• operators/reduce.ts
• operators/refCount.ts
• operators/repeat.ts
• operators/repeatWhen.ts
• operators/retry.ts
• operators/retryWhen.ts
• operators/sample.ts
• operators/sampleTime.ts
• operators/scan.ts
• operators/sequenceEqual.ts
• operators/share.ts
• operators/shareReplay.ts
• operators/single.ts
• operators/skip.ts
• operators/skipLast.ts
• operators/skipUntil.ts
• operators/skipWhile.ts
• operators/startWith.ts - needs N-args signature for observable inputs?
• operators/subscribeOn.ts
• operators/switchAll.ts
• operators/switchMap.ts
• operators/switchMapTo.ts
• operators/take.ts
• operators/takeLast.ts
• operators/takeUntil.ts
• operators/takeWhile.ts
• operators/tap.ts - see Refine subscribe and tap signatures #4159
• operators/throttle.ts
• operators/throttleTime.ts
• operators/throwIfEmpty.ts
• operators/timeInterval.ts
• operators/timeout.ts
• operators/timeoutWith.ts
• operators/timestamp.ts
• operators/toArray.ts
• operators/window.ts
• operators/windowCount.ts
• operators/windowTime.ts
• operators/windowToggle.ts
• operators/windowWhen.ts
• operators/withLatestFrom.ts - needs N-args signature for observable inputs?
• operators/zip.ts - see Rename all operators that are duplicates of static operators to xWith variants #3927 and needs N-args signature for observable inputs?
• operators/zipAll.ts
• scheduled/scheduled.ts

[cartant]

There is an issue with the Subject typings so that next can be called without an argument for Subject<void>, but the implementation makes Subject unsafe - see #2852. Whether or not anything can be done with this to make things safer, IDK, but we should have another look at it.

[cartant]

IMO, at some stage we should change signatures that involve errors to use unknown instead of any:

export interface NextObserver<T> {
  closed?: boolean;
  next: (value: T) => void;
  error?: (err: unknown) => void;
  complete?: () => void;
}

See #2646

However, this is likely to be an inconvenient breaking change. And it would be reasonable to argue that whilst the TypeScript typings for Promise use any for errors/rejection reasons, this library's typings should continue to use any.

Related Twitter conversation.

[benlesh]

startWith and endWith are taken care of here: #5247 #5246

[hmil]

Whether or not anything can be done with this to make things safer, IDK, but we should have another look at it.

Yes, please have another look at it.

The last comment on that issue says it all: You can just replace value?: T by value: T. When T is void, then the argument becomes optional.

const s1 = new Subject<void>();
s1.next(); // OK
s1.next(undefined); // OK

const s2 = new Subject<number>();
s2.next(); // error

The only problem is when someone does this:

const sAny = new Subject(); // No type parameter so defaults to `any`
sAny.next(); // Error because `any` is not mapped to an optional parameter

I don't know what people expect when they create a Subject without an explicit type. The default of Subject<any> is itself dangerous, and could be changed to void:

export declare class Subject<T = void> { /* ... */ }

const sVoid = new Subject(); // Defaults to Subject<void>.
sVoid.next(); // Works fine

If you like to have bugs in your code, then you can still create a subject of any with:

const sAny = new Subject<any>;

[cartant]

OMG, I received a DM question about interop observables and I was writing up some notes that I could turn into an article. The ergonomics of actually using the Subscribable type are horrible. The problem is the number of overloads that are in the type and - when used with from - RxJS always passes an observer - never separate callbacks - so including callbacks in the type is unnecessarily painful.

When #4532 is also taken into consideration, pretty much all aspects of this interop are 👎

[felixfbecker]

@cartant I replied to you in #4532 (comment) :)

[rraziel]

I will work on the following items' N-args signature/deprecating/renaming this week:

• operators/concat.ts
• operators/combineLatest.ts
• operators/zip.ts

I'll try to open a PR early just so it's visible and there is no overlapping work.

[backbone87]

idk, if i should add this here or create a new ticket:

the defaultIfEmpty operator has erroneous & inconvenient typing.

consider the follow example: const a = of(true).pipe(defaultIfEmpty(null));. this results in the following TS error:

Argument of type 'MonoTypeOperatorFunction<null>' is not assignable to parameter of type 'OperatorFunction<boolean, null>'.
  Types of parameters 'source' and 'source' are incompatible.
    Type 'Observable<boolean>' is not assignable to type 'Observable<null>'.
      Type 'boolean' is not assignable to type 'null'.ts(2345)

even explicitly typing a does not work const a: Observable<boolean | null> = of(true).pipe(defaultIfEmpty(null)); (same error as above)

even worse is passing no argument const a: Observable<boolean> = of(true).pipe(defaultIfEmpty());. this produces no error, which is wrong, because the observable should be of boolean | null.

edit: it gets even more worse: const a = of(undefined).pipe(defaultIfEmpty(undefined)); infers a as Observable<undefined> despite being Observable<undefined | null> in reality.

edit2: since this is a bug which should be addressed before ^7 i created a bug ticket: #6064

[cartant]

@backbone87

idk, if i should add this here or create a new ticket

As a general guide - for all repos - if you're unsure, open a new ticket. Anyway, thanks for opening #6064.