getAuth method incompatible with hot reloading

[markjaniczak]

Describe your environment

• Operating System version: MacOS Big Sur 11.2.1
• Browser version: Edge 88.0.705.74
• Firebase SDK version: 0.900.15
• Firebase Product: auth

Describe the problem

The getAuth function appears to always initialise a new instance when called. So in a Next.JS app that hot reloads you'll get the auth/already-initialized error.

The getApp method doesn't initialise a new app, it only returns the default or specified app. Combined with getApps, that pattern can be used to do an effective quick check to prevent duplicate instances:

// firebaseClient.js
import { initializeApp, getApps } from "firebase/app";

if (getApps().length === 0) {
  initializeApp({
    // ...config
  });
}

There doesn't appear to be a method for checking for existing instances before calling getAuth and I suspect the problem is the same for firestore, database etc. as the documentation suggests they also create a new instance when called.

[Feiyang1]

Thanks for the report. It will be fixed by #4519 once it's released

[retronav]

@markjaniczak Till the release comes out, you can follow up the conversation in #4510. That'll probably help you.
Thanks.