Middleware Mastery — Chapter Quiz

Question 1

1

What signature distinguishes an error middleware?

A(req, res)B(req, res, next)C(err, req, res, next) — 4 argsDAny function named errorHandler

Express recognizes error middleware by the 4-argument signature. Mount it last.

Question 2

2

A middleware should EITHER send a response OR call next(), never both.

TTrueFFalse

Doing both leads to "Cannot set headers after they are sent" errors. Always return after sending.

Question 3

3

Which is the standard middleware order?

ARoutes → middleware → error handlerBSecurity/logging → body parsers → routes → 404 → error handlerCError handler → middleware → routesDOrder does not matter

Security/observability/parsing happens first; routes in the middle; 404 and error handler at the very end.

Question 4

4

Where should app.use(express.json()) go?

ABefore routes that read req.bodyBAfter routesCAnywhere — it does not matterDInside the error middleware

Body parsers must run BEFORE route handlers that read req.body. Mount early in the chain.

Question 5

5

What does the factory pattern look like for middleware?

AA function returning a (req, res, next) functionBA class with init and handle methodsCAn object with before and after hooksDA Symbol

cors(), helmet(), rateLimit({...}) — all factories. Outer function takes config, returns the actual middleware.

Question 6

6

Forgetting to call ___ inside a middleware causes the request to hang.

If your middleware doesn't respond, it must call next() (or next(err)). Otherwise Express never advances the chain.

Question 7

7

Why mount helmet() early?

APerformanceBSecurity headers should be on every response — including errors and 404sCHelmet conflicts with routersDIt is required by Express

Mounted early, helmet ensures every response (success, error, 404, redirect) carries the security headers.

Question 8

8

Which middlewares are in a typical production starter pack?

Select all that apply.

All five are common. Mount them in the right order and the app is much safer/saner.

Test what you learned.