import * as firebase from "firebase/app";
import 'firebase/firestore'

const firebaseConfig = {
    apiKey: "api key",
    authDomain: "asdjfg.firebaseapp.com",
    databaseURL: "aksdjgh.firebaseio.com",
    projectId: "test-asdkjkgfsg",
    storageBucket: "tasdgaest-asdfg-asgafg.appspot.com",
    messagingSenderId: "asgas5554",
    appId: "1:asgasdgasgef76b"
};

const app = firebase.initializeApp(firebaseConfig);
const db = app.firestore();
export default db

Why does it say that app.firestore is not a function?

I have installed firebase & firebase-tools