Dans le cas de Babel / Flow, cela ressemblerait à ceci:
Disposition du répertoire
.
├── /build/                     # Compiled output for Node.js 6.x
├── /src/                       # Application source files
│   ├── db.js                   # Cloud SQL client for Postgres
│   ├── index.js                # Main export(s)
│   ├── someFuncA.js            # Function A
│   ├── someFuncA.test.js       # Function A unit tests
│   ├── someFuncB.js            # Function B
│   ├── someFuncB.test.js       # Function B unit tests
│   └── store.js                # Firebase Firestore client
├── .babelrc                    # Babel configuration
├── firebase.json               # Firebase configuration
└── package.json                # List of project dependencies and NPM scripts
src/index.js - Principales exportations
export * from './someFuncA.js';
export * from './someFuncB.js';
src/db.js - Client Cloud SQL pour Postgres
import { Pool } from 'pg';
import { config } from 'firebase-functions';
export default new Pool({
  max: 1,
  user: '<username>',
  database: '<database>',
  password: config().db.password,
  host: `/cloudsql/${process.env.GCP_PROJECT}:<region>:<instance>`,
});
src/store.js - Client Firebase Firestore
import firebase from 'firebase-admin';
import { config } from 'firebase-functions';
firebase.initializeApp(config().firebase);
export default firebase.firestore();
src/someFuncA.js - Fonction A
import { https } from 'firebase-functions';
import db from './db';
export const someFuncA = https.onRequest(async (req, res) => {
  const { rows: regions } = await db.query(`
    SELECT * FROM regions WHERE country_code = $1
  `, ['US']);
  res.send(regions);
});
src/someFuncB.js - Fonction B
import { https } from 'firebase-functions';
import store from './store';
export const someFuncB = https.onRequest(async (req, res) => {
  const { docs: regions } = await store
    .collection('regions')
    .where('countryCode', '==', 'US')
    .get();
  res.send(regions);
});
.babelrc
{
  "presets": [["env", { "targets": { "node": "6.11" } }]],
}
firebase.json
{
  "functions": {
    "source": ".",
    "ignore": [
      "**/node_modules/**"
    ]
  }
}
package.json
{
  "name": "functions",
  "verson": "0.0.0",
  "private": true,
  "main": "build/index.js",
  "dependencies": {
    "firebase-admin": "^5.9.0",
    "firebase-functions": "^0.8.1",
    "pg": "^7.4.1"
  },
  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-core": "^6.26.0",
    "babel-jest": "^22.2.2",
    "babel-preset-env": "^1.6.1",
    "jest": "^22.2.2"
  },
  "scripts": {
    "test": "jest --env=node",
    "predeploy": "rm -rf ./build && babel --out-dir ./build src",
    "deploy": "firebase deploy --only functions"
  }
}
$ yarn install                  # Install project dependencies
$ yarn test                     # Run unit tests
$ yarn deploy                   # Deploy to Firebase