observable-subject.ts

import { Injectable } from '@angular/core';
import {Subject} from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class IntermedioService {
  private observer = new Subject<string>();
  public errorMessage = this.observer.asObservable();

  constructor() { }

  updateMessage(message: string) {
    this.observer.next(message);
  }
}