javascript - Observable vs Subject and asObservable

Question

I am learning RxJs, I am seeking confirmation or correction on my assumption.

I am trying to make a public read only observable in a service that I can use .next() on in various places in my service class. I am wondering if this is the proper way to do it:

private myObservable = new Subject<T>();
public myObservable$: Observable<T> = this.myObservable.asObservable();

• The user can subscribe to myObservable$
• I can usemyObservable.next(...);

It works perfectly but I am experience enough to know that I may just be being an unwitting idiot (RxJS is huge). Is this correct pattern and correct object for said use case?

Answer 1

What you're doing is correct. There's however still a little shorter notation. Since Subject is already an Observable (it inherits the Observable class) you can leave the type checking to TypeScript:

private myObservable = new Subject<T>();
public myObservable$: Observable<T> = this.myObservable;

Any consumer of your service can subscribe to myObservable$ but won't be able to call myObservable$.next() because TypeScript won't let you do that (Observable class doesn't have any next() method).

This is actually the recommended way of doing it and RxJS internally never uses asObservable anyway. For more detailed discussion see:

• https://github.com/ReactiveX/rxjs/pull/2408

• https://github.com/ReactiveX/rxjs/issues/2391

See a very similar question: Should rxjs subjects be public in the class?