index.js

import 'react-native-gesture-handler';

import '@react-native-firebase/app';
import firestore from '@react-native-firebase/firestore';

import { registerRootComponent } from 'expo';

import App from './App';

if(__DEV__){
  firestore().terminate().then(() => {
    firestore().clearPersistence().then(() => {
      firestore().useEmulator('localhost', 8080);
    }).catch(() => {
      console.log('Error clearing persistence');
    });
  }).catch(() => {
    console.log('Error terminating');
  });
}

firestore();

// registerRootComponent calls AppRegistry.registerComponent('main', () => App);
// It also ensures that whether you load the app in Expo Go or in a native build,
// the environment is set up appropriately
registerRootComponent(App);