Rx.Subject.never() and Rx.Subject.empty() in rxjs7

[milahu]

static methods like never or empty are deprecated/removed in rxjs7

Rx.NEVER and Rx.EMPTY are typeof Observable

how should i create empty Subject and never Subject?

// index.ts
// rxjs version 7.5.5
var enableSubject = false;

var someSubject = enableSubject
  ? new Rx.Subject<SomeType>()
  : Rx.Subject.never() as Rx.Subject<SomeType>; // `Rx.Subject.never()` is rxjs6 api
// typescript error: Property 'never' does not exist on type 'typeof Subject'
// runtime error: TypeError: Rx.Subject.never is not a function

var someSubject = enableSubject
  ? new Rx.Subject<SomeType>()
  : Rx.EMPTY as Rx.Subject<SomeType>;
// typescript error: Conversion of type 'Observable<never>' to type 'Subject<SomeType>'
// may be a mistake because neither type sufficiently overlaps with the other.
// If this was intentional, convert the expression to 'unknown' first.

var someSubject = enableSubject
  ? new Rx.Subject<SomeType>()
  : Rx.EMPTY as unknown as Rx.Subject<SomeType>;
// runtime error: someSubject.next is not a function

var someSubject = new Rx.Subject<SomeType>();
if (!enableSubject) {
  someSubject.next = () => null; // monkey-patch to create a "never subject"
}
// this works, but its dirty

api docs

• https://rxjs.dev/api/index/const/NEVER
• https://rxjs.dev/api/index/const/EMPTY
• https://rxjs.dev/api/index/class/Subject
• https://rxjs.dev/api/index/class/Observable

stackoverflow

• RxJS5 - dummy observables

real code

• @pnpm/default-reporter

[voliva]

Not sure why would you need it....

But an empty subject is just

const subject = new Subject();
subject.complete();
// subject will now immediately complete when a new subscriber joins

And a "never" subject is just

const subject = new Subject();
// subject will never emit as long as you don't call `.next()` on it.

The concept of empty and never only applies for Observables. It doesn't really make sense to have a "never" subject, as a subject is both an observer and an observable.

[milahu]

const subject = new Subject();
subject.complete();

that works : )

documentation is sparse ... https://rxjs.dev/api/index/class/Subject#complete-
but there is https://rxjs.dev/guide/glossary-and-semantics#complete

Not sure why would you need it....

use case: logging with loglevels. depending on the current loglevel, i want to enable or disable the Subject

subject will never emit as long as you don't call .next() on it

that's the point ... i need a subject that emits nothing when i call subject.next()