Firebase config for Next.js

firebase-config-nextjs.js

import firebase from "firebase/app";
import "firebase/auth";
import "firebase/firestore";
import "firebase/app-check";

const CONFIG = {
  apiKey: process.env.NEXT_PUBLIC_FIREBASE_KEY,
  authDomain: process.env.NEXT_PUBLIC_FIREBASE_DOMAIN,
  projectId: process.env.NEXT_PUBLIC_FIREBASE_PROJECT_ID,
  databaseURL: process.env.NEXT_PUBLIC_FIREBASE_DATABASE_URL,
  storageBucket: process.env.NEXT_PUBLIC_FIREBASE_STORAGE_BUCKET,
  messagingSenderId: process.env.NEXT_PUBLIC_FIREBASE_SENDER_ID,
  appId: process.env.NEXT_PUBLIC_FIREBASE_APP_ID,
  measurementId: process.env.NEXT_PUBLIC_FIREBASE_MEASUREMENT_ID,
};

let app;

if (!firebase.apps.length) {
  firebase.initializeApp(CONFIG);
} else {
  firebase.app(); // if already initialized, use that one
}

const appCheck = firebase.appCheck(app);

export default app;
export { app };
export { appCheck };