How to use serverless functions with Next.js?

How to use serverless functions with Next.js?

Next.js has gained popularity in the web development community for its ease of use, performance, and versatility. One of its powerful features is the support for serverless functions, which allows developers to run backend code without having to manage a server infrastructure. This feature is particularly useful for building scalable applications, handling API requests, server-side logic, or integrating with databases and other services. In this article, we'll explore how to use serverless functions with Next.js, covering setup, development, and deployment.

Understanding Serverless Functions in Next.js


Serverless functions, also known as API routes in Next.js, enable you to create server-side logic that is hosted on serverless computing platforms. These functions are event-driven and execute in response to requests. In the context of Next.js, serverless functions are written as Node.js functions and can be deployed as individual endpoints within your Next.js application.

Benefits of Using Serverless Functions

  • Scalability: Automatically scales with the number of requests.
  • Cost-Effectiveness: Pay only for the compute time you use.
  • Simplicity: Simplify backend code management and deployment.
  • Flexibility: Easily integrate with databases, authentication, and external APIs.

Setting Up a Next.js Project

Before diving into serverless functions, ensure you have a Next.js project set up. If you're starting from scratch, follow these steps:

  1. Install Node.js: Ensure you have Node.js installed on your system. You can download it from the official Node.js website.

  2. Create a Next.js App: Use the create-next-app CLI to set up a new Next.js project. Open your terminal and run:

    npx create-next-app@latest my-next-app
    cd my-next-app
  3. Start the Development Server: Run npm run dev to start the local development server. You can now access your Next.js app at http://localhost:3000.

Creating Serverless Functions

Serverless functions in Next.js are created in the pages/api directory. Each file within this directory is treated as an API endpoint.

Example: A Simple API Endpoint

  1. Create a New Function: Inside your Next.js project, navigate to the pages/api directory and create a new file named hello.js.

  2. Write the Function Code:

    // pages/api/hello.js
    export default function handler(req, res) {
      res.status(200).json({ message: "Hello World!" });
  3. Testing Your Endpoint: Start your development server if it's not running (npm run dev) and visit http://localhost:3000/api/hello in your browser. You should see the JSON response { "message": "Hello World!" }.

Handling Different HTTP Methods

You can handle different HTTP methods (GET, POST, etc.) within the same API route by checking the req.method property.

// pages/api/post.js
export default function handler(req, res) {
  if (req.method === "POST") {
    // Handle POST request
    res.status(200).json({ message: "Handling POST request" });
  } else {
    // Handle any other HTTP method
    res.setHeader("Allow", ["POST"]);
    res.status(405).end(`Method ${req.method} Not Allowed`);

Deploying Your Next.js Application with Serverless Functions


Deploying a Next.js application with serverless functions is straightforward, especially if you use Vercel, the platform created by the creators of Next.js. Vercel provides seamless integration for Next.js applications, automatically handling the deployment of your serverless functions.

Deploying with Vercel

  1. Sign Up/Login to Vercel: Visit Vercel's website and sign up or log in.

  2. Connect Your GitHub/GitLab/Bitbucket: Connect your repository hosting service to easily deploy projects.

  3. Import Your Next.js Project: Click on "New Project", select your Next.js repository, and import it.

  4. Deploy: Configure your project settings if necessary and click "Deploy". Vercel will automatically detect it as a Next.js project and deploy it, including your serverless functions.

Alternative Deployment Options

While Vercel is the most integrated option for Next.js applications, you can also deploy your Next.js app with serverless functions on other cloud platforms like AWS Lambda, Azure Functions, or Google Cloud Functions. Each platform has its own set of tools and services for deploying serverless functions, so you'll need to follow the specific instructions for your chosen platform.

Advanced Usage of Serverless Functions in Next.js

Expanding upon the basics, let's delve into more advanced concepts and practices that can enhance your use of serverless functions within Next.js applications. These include environment variables, middleware, and connecting to a database.

Leveraging Environment Variables

For any application that requires API keys, connection strings, or any sensitive information, environment variables are essential. They help keep your secrets safe and separate from your codebase, which is especially important for public repositories.

  1. Setting up Environment Variables: Create a .env.local file at the root of your Next.js project. Define your variables here, like so:

  2. Using Environment Variables in Your Serverless Functions: Access these variables using process.env:

    // pages/api/secret.js
    export default function handler(req, res) {
      const secretKey = process.env.API_SECRET_KEY;
      // Use secretKey for your logic
      res.status(200).json({ message: "Secret Key used!" });

Implementing Middleware

Next.js supports middleware, allowing you to run code before a request is completed. You can use middleware for various purposes, such as authentication, logging, and setting headers globally.

  1. Creating Middleware: Create a _middleware.js file in your pages or pages/api directory. Here's an example that adds a custom header to every response:

    // pages/_middleware.js
    import { NextResponse } from "next/server";
    export function middleware(request) {
      const response =;
      response.headers.set("X-Custom-Header", "MyValue");
      return response;
  2. Conditional Logic: Middleware can run conditionally based on the request. For instance, you might want to authenticate API routes:

    // pages/api/_middleware.js
    import { NextResponse } from "next/server";
    export function middleware(req) {
      const { pathname } = req.nextUrl;
      if (pathname.startsWith("/api/secret")) {
        const token = req.headers.get("Authorization");
        if (!token || token !== `Bearer your-secret-token`) {
          return new Response(JSON.stringify({ error: "Not Authorized" }), {
            status: 401,
            headers: {
              "Content-Type": "application/json",

Connecting to a Database

Serverless functions in Next.js can easily connect to databases, making it suitable for full-stack applications. Here’s a simple example using MongoDB:

  1. Install MongoDB Driver: Run npm install mongodb.

  2. Create a Utility for Database Connection:

    // lib/mongodb.js
    import { MongoClient } from "mongodb";
    const uri = process.env.DATABASE_URL;
    const options = {
      useUnifiedTopology: true,
      useNewUrlParser: true,
    let client;
    let clientPromise;
    if (!process.env.DATABASE_URL) {
      throw new Error("Please add your Mongo URI to .env.local");
    if (process.env.NODE_ENV === "development") {
      // In development mode, use a global variable so the database connection
      // is preserved between hot reloads in Next.js.
      if (!global._mongoClientPromise) {
        client = new MongoClient(uri, options);
        global._mongoClientPromise = client.connect();
      clientPromise = global._mongoClientPromise;
    } else {
      // In production mode, it's best to not use a global variable.
      client = new MongoClient(uri, options);
      clientPromise = client.connect();
    export default clientPromise;
  3. Using the Database Connection in an API Route:

    // pages/api/data.js
    import clientPromise from "../../lib/mongodb";
    export default async function handler(req, res) {
      try {
        const client = await clientPromise;
        const db = client.db("your-database-name");
        const data = await db.collection("your-collection").find({}).toArray();
      } catch (e) {
        res.status(500).json({ error: "Unable to fetch data" });


Integrating serverless functions into your Next.js application can significantly enhance its capabilities, allowing you to build dynamic, scalable, and cost-effective web applications. Whether you're handling API requests, server-side processing, or integrating with other services, serverless functions provide a powerful and flexible solution. By following the steps outlined in this guide, you'll be well on your way to leveraging serverless functions in your Next.js projects.

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