App Router API Middleware

Show how to implement middleware with the new App Router to perform server-side checks, like authentication or redirections before rendering a page.
const express = require('express');
const app = express();

// Middleware for authentication
const checkAuth = (req, res, next) => {
  // Insert your authentication logic here
  const userIsAuthenticated = true; // Just for example

  if (!userIsAuthenticated) {
    res.status(401).send('User is not authenticated');
  } else {

// Middleware for redirection
const redirectionMiddleware = (req, res, next) => {
  // Insert your redirection logic here
  const shouldBeRedirected = false; // Just for example

  if (shouldBeRedirected) {
  } else {
Defines two pieces of middleware: one for authenticating the user and another for redirecting the request. If the user is not authenticated, a 401 response is sent. If a redirection condition is met, the request is redirected to another page.

Applies the authentication and redirection middleware to all incoming requests.
app.get('/protected-page', (req, res) => {
  // This route is protected, and user will see it only if authenticated and not redirected
  res.send('Welcome to the protected page!');

app.listen(3000, () => {
  console.log('Server running on port 3000');
Creates a protected route that will only render if the user passes the authentication and redirection middleware. The server listens on port 3000.