Middleware in Next.js

In Next.js, Middleware allows you to run logic before a request is completed, enabling powerful features like authentication, redirects, and request modifications.

🧠 How Middleware Works:

Middleware runs before the request reaches a page or an API route.
It can inspect and modify the request, perform checks (like authentication), or rewrite/redirect responses.

Example of Middleware for authentication:

javascript1// middleware.js
2import { NextResponse } from 'next/server';
3
4export function middleware(req) {
5  const token = req.cookies.get('token');
6  if (!token) {
7    return new NextResponse('Unauthorized', { status: 401 });
8  }
9  return NextResponse.next();
10}

In this example, the middleware checks for a token in cookies. If it's missing, the request is blocked with a 401 response.

In short:

Middleware runs code before routing completes.
Great for auth checks, logging, redirects, and other pre-processing logic.