Firebase is not defined

hi everybody… please is there a tutorial to do the firebase setup? i am getting this error:

firebase is not defined

my app.js:
import $$ from ‘dom7’;
import Framework7 from ‘./framework7-custom.js’;
import firebase from ‘firebase/app’;
import ‘firebase/auth’;

my code:

firebase.auth().settings.appVerificationDisabledForTesting = false;
var phoneNumber = “+12345678910”;
var testVerificationCode = “123456”;
var appVerifier = new firebase.auth.RecaptchaVerifier(‘recaptcha-container’);
firebase.auth().signInWithPhoneNumber(phoneNumber, appVerifier)
.then(function (confirmationResult) {
return confirmationResult.confirm(testVerificationCode);
}).catch(function (error) {
console.log(‘erreur SMS not sent’);