State with RxJS

state.ts

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

export interface Todo {
  text: string;
  complete: boolean;
}

export interface State {
  todos: Todo[];
}

const initialState: State = {
  todos: []
}

export class Store {
  private subject = new BehaviorSubject<State>(initialState);
  private store = this.subject.asObservable().pipe(distinctUntilChanged());

  private get value() {
    return this.subject.getValue();
  }

  set(name: keyof State, state: any) {
    this.subject.next({ ...this.value, [name]: state });
  }

  select(name: keyof State): Observable<any> {
    return this.store.pipe(pluck(name));
  }
}