Module Overview

What You’ll Learn

• Explain what Express middleware is and how it processes a request
• Use Express’s built-in middleware and well-known third-party packages
• Write your own custom middleware

💡 Why this module matters: Nearly everything an Express app does beyond a single route handler, parsing JSON bodies, logging requests, setting security headers, handling cookies, runs through middleware. Understanding the pattern unlocks how the rest of a real Express app is actually built.

What’s Covered

• Express middleware, the request-handling pipeline every request flows through.
• Built-in middleware, including express.json(), express.urlencoded(), and static file serving.
• Custom middleware, writing your own function to run on every matching request.
• Morgan, logging every incoming request.
• Helmet, setting security-related HTTP headers.
• CORS, controlling which origins can call your API.
• Cookie parser, reading cookies sent with a request.
• Compression, shrinking response sizes automatically.

Hands-On

By the end of this module, you’ll have built a custom logging middleware from scratch, and wired up a real Express app with JSON parsing, security headers, CORS, and cookie support.

Next module: error handling, what happens when something inside a route or middleware goes wrong.