Create filtered Subject to Observable in Angular

Question

Hi I have a private Subject that I do not want to expose, so I am creating different Observables from the single Subject:

public numberChange$: Observable<number>;
public oddChange$: Observable<number>;
public evenChange$: Observable<number>;
private number: Subject<number>;
constructor() {
  this.number = new Subject<number>();
  this.numberChange$ = this.number.asObservable();
  this.oddChange$ = this.number.filter(n => n % 2 === 1).asObservable();
  this.evenChange$ = this.number.filter(n => n % 2 === 0).asObservable();
}

So that others can subscribe to numberChange$ if they want to know when the number has changed. If they want to know ONLY when the change is an odd number, they can subscribe to oddChange$. Same goes for evenChange$.

The code above does not work because after this.number.filter() I cannot call asObservable() anymore. How do you fix the code above to achieve what I have described?

Answer 1

An Observable is returned from Observable.filter. So there isn't a need to call asObservable(), just subscribe to the returned value.

this.number = new Subject<number>();
this.numberChange$ = this.number.asObservable();
this.oddChange$ = this.number.filter(n => n % 2 === 1);
this.evenChange$ = this.number.filter(n => n % 2 === 0);
this.oddChange$.subscribe((x) => { console.log(x) } );