[RxJS] Subject asObservable() method

You can create your own state store, not using any state management libraray.

You might have seen the partten: People create a Subject, then use abObservable() method.

export class State {
  private prevState: INEO[];
  private neoStoreSubject: BehaviorSubject<INEO[]>;
  neoStore$: Observable<INEO[]>;

  protected constructor() {
    this.neoStoreSubject = new BehaviorSubject([]);
    this.neoStore$ = this.neoStoreSubject.asObservable();
  }

  ...
}

Main reason for that is, we want to keep:

this.neoStoreSubject = new BehaviorSubject([]);

as private, we don't want any component can call .next() method to update store. The job for updating store should only happen in 'State' class.

// State class
  setNeoStore(neoList: INEO[]) {
    this.setPrevState();
    this.neoStoreSubject.next(neoList);
    this.dismissError();
  }

For component, we can subscribe this.neoStore$. it can only receive the data, but not update the store directly.

// From Component

  biggerFasterNeo$ = this.data.neoStore$.pipe(
    filter(neoList => !!neoList === true),
    map(neoList => neoList.filter(neo => {
      if (neo.estimated_diameter > 0.5 || neo.relative_velocity > 50000) {
        return neo;
      }
    }))
  );

For component