Express.js Roadmap

Express is a small web framework on top of Node.js.

It helps you build APIs using routes, middleware, request objects, response objects, and centralized error handling.

Study order

Routes -> Request input -> Middleware -> Controllers -> REST -> Validation -> Auth -> Errors -> API exercises

Do not start with project folders. First understand how one request moves through Express.

What matters most

• Routes match HTTP method and URL.
• Middleware runs in order.
• Controllers should handle HTTP concerns.
• Services should hold business logic.
• Errors should be centralized.
• Auth has two parts: authentication and authorization.

Interview angle

If asked about Express, explain the request lifecycle: request enters the app, matching middleware/routes run, handlers produce a response, and errors flow to error-handling middleware.