How to Use Firebase Functions With Express and Firestore for a Full Backend API

#firebase #serverless #api #backend

If you're looking to deploy a full-featured serverless backend using Firebase, pairing Express with Firestore inside Firebase Cloud Functions is a flexible and powerful setup. This guide shows you how to deploy an Express API using Firebase Functions, backed by Firestore as your NoSQL database.

Step 1: Initialize Firebase Project

npm install -g firebase-tools
firebase login
firebase init functions

Choose:

Functions (yes to TypeScript or JavaScript)
Firestore if you want to test locally too
Install dependencies

Step 2: Set Up Express in Your Functions

// functions/index.js or functions/src/index.ts
const functions = require("firebase-functions");
const admin = require("firebase-admin");
const express = require("express");

admin.initializeApp();
const db = admin.firestore();

const app = express();

app.get("/users", async (req, res) => {
  const snapshot = await db.collection("users").get();
  const users = snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() }));
  res.json(users);
});

app.post("/users", async (req, res) => {
  const user = req.body;
  const ref = await db.collection("users").add(user);
  res.status(201).json({ id: ref.id });
});

exports.api = functions.https.onRequest(app);

Step 3: Enable Firestore Rules

In firestore.rules, allow reads/writes for testing (don’t use in prod):

service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write: if true;
    }
  }
}

Step 4: Deploy Your Backend

firebase deploy --only functions

You’ll get a URL like:

https://your-region-your-project.cloudfunctions.net/api/users

Step 5: Test It

# GET users
curl https://your-url/api/users

# POST user
curl -X POST https://your-url/api/users -H "Content-Type: application/json" -d '{"name":"Jane"}'

Conclusion

This setup gives you a scalable, serverless backend with full CRUD API capabilities, using Firebase’s managed services. You can layer on authentication, validation, and complex querying with minimal infrastructure concerns.

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