[firebase_database]: connect to different database of app

How can I connect to another database of the same app?

I can get the database instance with the below code but it always connects to the default database.
```
var app = fb.initializeApp();
fb.database(app); // this will connect to default database of the app.
```

https://firebase.google.com/docs/reference/js/database.md#getdatabase

