Why does subject.pipe(op1(), ...) returns an AnonymousSujbect

[LcsGa]

I've always thought that calling the .pipe() method to a subject (with at least one operator) resulted in an observable and thus, I didn't need to call .asObservable too. It appears that I was wrong as I tried to log something like subject.pipe(op1()) and it logged an AnonymousSubject on which I can still use the next, error and complete methods.

I tried to find out in the source code why this happens but couldn't find anywhere it should transform a subject into an anonymousSubject... Can you please explain to me where this happens 😅?

(NB: Here is an example of what I did to figure out this https://stackblitz.com/edit/rxjs-nw7h6x?file=index.ts)

[voliva]

This is because pipe applies the operators one by one, and those use "lift", which keeps the original constructor intact #60

The only problem is that this can't be easily done with TS, so the type definition for pipe returns an Observable, but it actually returns whatever the original observable type's.

Related #6148 and #7201, quoting Ben Lesh:

The only issue I see is currently RxJS supports the composition of our subject variants through the operator chain, via lift. This is a little known aspect of RxJS that isn't used much, in no smart part because TypeScript can't support it:

const subject = new Subject<number>()

const lifted = subject.pipe(map(n => n + '?'), map(s => s + '!');

lifted.subscribe(console.log);

(lifted as any).next(42); // logs "42?!"

This won't apply for v8.x, as lift was removed: #7202

[LcsGa]

Thank you very much for your very clear answer! 😁