firebaseInit.js

// require with Promise wrapper / dynamic import()
import importFirebase from 'firebaseImport'

export default function firebase() {
  return importFirebase().then((firebase) => {
    // do that ever you need here.
    // something like: 
    const app = firebase.initializeApp({
      apiKey: '<your-api-key>',
      authDomain: '<your-auth-domain>',
      databaseURL: '<your-database-url>',
      storageBucket: '<your-storage-bucket>',
      messagingSenderId: '<your-sender-id>'
    })
    
    // return actully usable objects:
    return {
      database: app.database()
      auth: app.auth()
    }
  })
}