Project setup and initialization

identify the Firebase project (client SDK)

The config object stores credentials to identify the Firebase project when interacting with Google servers. These credentials are not sensitive or confidential per se since they only serve to identify the project, and they are exposed on the client.

const firebaseConfig = {
    apiKey: "....",
    authDomain: ".....firebaseapp.com",
    projectId: "....",
    storageBucket: ".....firebasestorage.app",
    messagingSenderId: "....",
    appId: "....",
}

register one or more configs

We give the config to the client SDK. It returns a helper object that we initialize other services with.

const app = initializeApp(firebaseConfig)

When working with several Firebase projects, we get a helper for each project. The first helper has a "[DEFAULT]" internal string identifier. We must provide a string identifier for additional project we want to work with.

const app1 = initializeApp(firebaseConfig1)
const app2 = initializeApp(firebaseConfig2, "two")

When initializing the admin SDK from Cloud Functions, the environment is automatically configured: we don't have a config object at all, and we get a helper config-less.

const app = initializeApp()