How to create a new collection using Firestore v9

You’re might — like me — already familiar with Firestore <=8, and you now want to try out the new features in v9. There have been made some clear changes, working with collections and documents.

When I saw the documents, how to migrate from 8 to 9:
https://firebase.google.com/docs/firestore/manage-data/add-data#set_a_document

I was still pretty confused. And for that reason, I will try to explain how I made it much more simple, with this small amount of codes.

Let’s start with the firebase config file

/app/firebase/firebase.js 
import { initializeApp } from "firebase/app"; 
import { getFirestore } from "firebase/firestore"; 
const firebaseConfig = { 
  apiKey: process.env.NEXT_PUBLIC_API_KEY, 
  authDomain: process.env.NEXT_PUBLIC_AUTH_DOMAIN, 
  databaseUrl: process.env.NEXT_PUBLIC_DATABASE_URL, 
  projectId: process.env.NEXT_PUBLIC_PROJECT_ID, 
  storageBucket: process.env.NEXT_PUBLIC_STORAGE_BUCKET,
  messagingSenderId: process.env.NEXT_PUBLIC_MESSAGING_SENDER_ID, 
  appId: process.env.NEXT_PUBLIC_APP_ID, 
  measurementId: process.env.NEXT_PUBLIC_MEASUREMENT_ID
}; 
const app = initializeApp(firebaseConfig); 
const db = getFirestore(app);