Follow one task request
Trace a browser request through the API into PostgreSQL and back.
HTTP is the agreement between client and server
Understand methods, status codes, headers, and resource identifiers.
Node runs JavaScript outside the browser
Separate the language, runtime, process, and application configuration.
Waiting and blocking are different
Explain asynchronous database calls and CPU work in the Node event loop.
Middleware order changes what a route can trust
Understand the Express request pipeline and the special case for webhook bodies.
Validate where untrusted data enters
Separate frontend feedback, runtime validation, and database guarantees.