firebase.js

// @flow
import * as firebase from "firebase";
import "firebase/firestore";

const config = {
    apiKey: "AIzaSyD",
    authDomain: "react-native.firebaseapp.com",
    databaseURL: "https://react-native.firebaseio.com",
    projectId: "react-native",
    storageBucket: "react-native.appspot.com",
    messagingSenderId: "111"
};

export default class Firebase {

    static firestore: firebase.firestore.Firestore;
    static auth: firebase.auth.Auth;
    static storage: firebase.storage.Storage;

    static init() {
        firebase.initializeApp(config);
        Firebase.auth = firebase.auth();
        Firebase.firestore = firebase.firestore();
        Firebase.storage = firebase.storage();
    }
}