In Next.js, API routes allow you to build backend functionality within your application. These routes run on the server and can handle requests like REST APIs.

📌 Creating an API Route

API routes are placed inside the pages/api/ directory. Each file inside this directory is mapped to /api/<filename>.

🔹 Basic Example

Create pages/api/hello.js:

javascript
export default function handler(req, res) {  if (req.method === "GET") {    res.status(200).json({ message: "Fetching user data" });  } else if (req.method === "POST") {    res.status(201).json({ message: "User created" });  } else {    res.setHeader("Allow", ["GET", "POST"]);    res.status(405).end(`Method ${req.method} Not Allowed`);  }}

• GET /api/user → Returns "Fetching user data"

• POST /api/user → Returns "User created"

• Other methods → Returns 405 Method Not Allowed

📌 Using Query Parameters

🔹 Example: Get User by ID

Create pages/api/user/[id].js:

javascript
export default function handler(req, res) {  if (req.method === "POST") {    const { name, email } = req.body;    res.status(201).json({ message: `User ${name} with email ${email} created` });  } else {    res.status(405).json({ message: "Method Not Allowed" });  }}

• Send a POST request with JSON body { "name": "John", "email": "john@example.com" }

• Response: { "message": "User John with email john@example.com created" }

📌 Connecting to a Database

Next.js API routes work well with databases like PostgreSQL, MongoDB, or Firebase.

🔹 Example: Fetch Data from PostgreSQL

Using pg for PostgreSQL:

javascript
import { Pool } from "pg";const pool = new Pool({  user: "your_user",  host: "localhost",  database: "your_db",  password: "your_password",  port: 5432,});export default async function handler(req, res) {  if (req.method === "GET") {    const { rows } = await pool.query("SELECT * FROM users");    res.status(200).json(rows);  } else {    res.status(405).json({ message: "Method Not Allowed" });  }}

• GET /api/users → Returns users from PostgreSQL.

📌 Middleware in API Routes

Middleware can be used for authentication, logging, etc.

🔹 Example: Authentication Middleware

javascript
export function withAuth(handler) {  return async (req, res) => {    const token = req.headers.authorization;    if (!token || token !== "your-secret-token") {      return res.status(401).json({ message: "Unauthorized" });    }    return handler(req, res);  };}// Apply to an API routeexport default withAuth(async function handler(req, res) {  res.status(200).json({ message: "Authenticated request" });});

📌 When to Use API Routes?

✅ When you need server-side logic (e.g., fetching data from a database).
✅ When handling form submissions.
✅ When interacting with third-party APIs securely.
❌ Not recommended for real-time updates (use WebSockets or Next.js Edge Functions).