State Service where all Feature State's extend from

state.service.ts

import { BehaviorSubject, Observable } from 'rxjs';
import { distinctUntilChanged, map } from 'rxjs/operators';

export class StateService {
  private state$!: BehaviorSubject<any>;

  protected get state(): any {
    return this.state$.getValue();
  }

  constructor(initialState: any) {
    this.state$ = new BehaviorSubject<any>(initialState);
  }

  protected select<K>(mapFn: (state: any) => K): Observable<K> {
    return this.state$.asObservable().pipe(
      map((state: any) => mapFn(state)),
      distinctUntilChanged()
    );
  };

  // Return state snapshot after merging partial state with full obj state
  protected setState(newState: Partial<any>) {
    this.state$.next({
      ...this.state,
      ...newState
    })
  }
}