Chapter quiz · Building REST APIs

Test what you learned.

8 questions on Building REST APIs. Pass 70% to clear the chapter.

Quiz

Building a REST API — Chapter Quiz

Eight questions on koa-bodyparser, controllers/services split, validation 422, pagination, content negotiation, ctx.throw, and versioning.

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Question 1
1
After adding koa-bodyparser middleware, where does Koa place the parsed JSON request body?
Actx.bodyBctx.request.bodyCctx.req.bodyDctx.json
koa-bodyparser attaches the parsed body to ctx.request.body. Do not confuse with ctx.body, which is the **response** body you set to send data back to the client.
Question 2
2
Which HTTP status code should be returned when a request body fails validation?
A400 Bad RequestB401 UnauthorizedC422 Unprocessable EntityD500 Internal Server Error
422 signals that the syntax was valid but the data failed semantic validation (missing required fields, wrong types, etc.). 400 is acceptable too, but 422 is more semantically precise for validation errors.
Question 3
3
How does ctx.throw(404, 'Not found') differ from throw new Error('Not found')?
Actx.throw creates an HttpError with .status set, which error middleware can inspect; plain throw defaults to 500BThey are identicalCctx.throw terminates the processDPlain throw sets ctx.status automatically
ctx.throw uses the http-errors package to create an error with a .status property and .expose = true so the message is safe to send to the client. Error middleware reads err.status to set the response code.
Question 4
4
What is a simple cursor-based or offset/limit pagination response envelope?
A{ data: [...], total: N, page: P, limit: L }B{ items: [...] } onlyC{ results: [...], next: \"cursor\" }DBoth A and C are valid envelopes depending on strategy
Offset/limit APIs return { data, total, page, limit }. Cursor-based APIs return { results, next }. Both are valid; choose based on data size and mutation frequency.
Question 5
5
How do you implement API versioning via URL path in a Koa app using @koa/router?
ASet router.prefix(\"/v1\") and mount a second router with prefix /v2BAdd a version query parameter to every routeCUse separate Koa apps on separate portsDSet ctx.apiVersion in middleware
Create one router per version, call router.prefix('/v1') (or /v2), and mount both with app.use. Each version's routes are isolated and can differ independently.
Question 6
6
Content negotiation via ctx.accepts('json', 'html') returns the best match from the Accept header, or false if none match.
TTrueFFalse
ctx.accepts() compares the request Accept header against your listed types and returns the best match string or false. Use it to serve JSON to API clients and HTML to browsers from the same route.
Question 7
7
A controller should delegate business logic to a ___ layer, keeping route handlers thin.
The controller/service split is a common pattern: controllers handle HTTP concerns (parsing body, setting status), services contain business logic and DB access. This makes services independently testable.
Question 8
8
Which practices improve a Koa REST API's reliability and maintainability?
Select all that apply.
AValidate request bodies with a schema library (Zod, Joi) before processingBReturn consistent error envelopes { error: { code, message } }CPut all DB queries directly in the router handlerDUse ctx.throw with appropriate status codes instead of generic 500s
Schema validation, consistent error envelopes, and precise HTTP status codes are all best practices. Embedding DB queries directly in route handlers couples concerns and makes testing harder.