Node.js Middleware

Step-by-Step Guide to Using Middleware in Node.js

1. Setting Up an Express Server

First, install Express.js if you haven't already:

npm install express

const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.send('Welcome to Node.js Middleware Tutorial!');
});

app.listen(3000, () => {
  console.log('Server running on http://localhost:3000');
});

Run the server with:

node server.js

2. Creating a Simple Middleware Function

Middleware functions take three arguments:

req (request)
res (response)
next (function to move to the next middleware)

Add a simple logging middleware before routes:

const logger = (req, res, next) => {
  console.log(`${req.method} request to ${req.url}`);
  next(); // Move to the next middleware or route
};

app.use(logger);

3. Using Built-in Middleware

Express provides built-in middleware like express.json() for parsing JSON data:

app.use(express.json()); // Parses incoming JSON requests

Example POST route:

app.post('/data', (req, res) => {
  res.json({ received: req.body });
});

4. Using Third-Party Middleware

You can install third-party middleware for additional features. Example: cors to allow cross-origin requests.

Install cors:

npm install cors

Use it in your app:

const cors = require('cors');
app.use(cors()); // Enables cross-origin requests

5. Creating an Authentication Middleware

Middleware can be used for user authentication before reaching protected routes.

const authenticate = (req, res, next) => {
  const token = req.headers['authorization'];
  if (!token) return res.status(403).json({ error: 'Access Denied' });

  next(); // Proceed to the next middleware/route
};

app.get('/protected', authenticate, (req, res) => {
  res.send('Welcome to the protected route!');
});

6. Error Handling Middleware

A global error handler catches all errors and prevents app crashes:

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send({ error: 'Something went wrong!' });
});

Conclusion

Middleware is an essential part of Express.js for handling requests, authentication, logging, and error handling. This guide covered:
✅ Creating custom middleware
✅ Using built-in middleware
✅ Implementing authentication middleware
✅ Using third-party middleware like cors
✅ Handling errors with global middleware

Now, you can enhance your Express.js applications with middleware to improve security, performance, and flexibility! 🚀

NODEJS