create-observables-rxfire.js

import { collection } from 'rxfire/firestore';
import { map } from 'rxjs/operators';

// Query for California
var californiaRef = citiesRef.where("state", "==", "CA");

// Query for Colorado
var coloradoRef = citiesRef.where("state", "==", "CO");

// Create Observables ready for subscribe().
var california$ = collection(californiaRef)
  .pipe(map(cities => cities.map(c => c.data())));
var colorado$ = collection(coloradoRef)
  .pipe(map(cities => cities.map(c => c.data())));;