In Part 1, we introduced Express.js as a powerful framework for Node.js web development and explored the concept of middleware—functions that process HTTP requests during the request-response cycle. Middleware has access to the req, res, and next objects, enabling tasks like modifying requests, sending responses, or passing control to the next handler. We covered the middleware function signature, its execution flow, and how to implement application-level and router-level middleware with examples like logging and basic authentication. Part 2 dives into built-in, third-party, and error-handling middleware, real-world use cases, and best practices for effective middleware development.

Built-in Middleware

Express provides several built-in middleware functions that simplify common tasks. These are included with Express and require no external dependencies. Below are two widely used examples:

express.json()

Parses incoming requests with JSON payloads, populating req.body with the parsed data.

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

// Parse JSON payloads
app.use(express.json());

// Example route using parsed JSON
app.post('/user', (req, res) => {
  const { name, email } = req.body;
  res.json({ message: `Received: ${name}, ${email}` });
});

app.listen(3000, () => console.log('Server running on port 3000'));