Chapter quiz · Data & Realtime

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8 questions on Data & Realtime. Pass 70% to clear the chapter.

Quiz

Data, Files & Real-Time — Chapter Quiz

Eight questions on DB pooling, ORM, multipart uploads, koa-static, streaming ctx.body, SSE, websockets, ETag caching, and background jobs.

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Question 1
1
Why should you use a connection pool instead of creating a new DB connection per request?
AConnection pools encrypt traffic automaticallyBEstablishing TCP + TLS + auth handshakes is expensive; a pool reuses warm connections, reducing latencyCPools are required by all databasesDA pool prevents SQL injection
Connection setup (TCP, TLS, DB auth) can take 20–100 ms. A pool keeps a set of warm connections ready, so queries are served with sub-millisecond connection overhead.
Question 2
2
How do you serve a Node.js ReadStream as the HTTP response body in Koa?
Actx.body = streamBctx.send(stream)Cstream.pipe(ctx.res)Dctx.response.stream = stream
Koa detects that ctx.body is a stream and pipes it to the response automatically, setting Transfer-Encoding: chunked. This works for file downloads, generated content, and proxied responses.
Question 3
3
Which package handles multipart/form-data file uploads in a Koa app?
Akoa-bodyparserB@koa/multer or busboy-based middleware like koa-bodyCkoa-staticDkoa-compress
koa-bodyparser does not handle multipart. @koa/multer (a Koa port of multer) or koa-body (wraps busboy) parse multipart/form-data and expose uploaded files on ctx.request.files.
Question 4
4
How do you implement Server-Sent Events (SSE) in Koa?
ASet ctx.body to a PassThrough stream and write data: ...\n\n chunks; set Content-Type: text/event-streamBUse ctx.sse.send(\"message\")CSet ctx.status = 206 and write binary chunksDSSE is not possible with Koa
SSE uses a long-lived HTTP response with Content-Type: text/event-stream. Assign a readable/passthrough stream to ctx.body, write SSE-formatted chunks (data: ...\n\n), and Koa streams them to the client.
Question 5
5
How do you attach a WebSocket server to a Koa app without a separate port?
Aapp.useWebSocket(wss)BPass app.callback() to http.createServer, then pass the server to new WebSocket.Server({ server })CSet ctx.upgrade = true in middlewareDWebSocket servers require a separate port from HTTP
app.callback() returns a standard Node request listener. Pass it to http.createServer to get an http.Server, then hand that server to ws (or socket.io) so HTTP and WebSocket share port 80/443.
Question 6
6
Setting ctx.set('ETag', hash) and checking ctx.fresh lets Koa respond with 304 Not Modified for unchanged resources.
TTrueFFalse
After setting ETag (and/or Last-Modified), ctx.fresh returns true when the client's If-None-Match / If-Modified-Since headers match. Set ctx.status = 304 and skip the body to send a conditional response.
Question 7
7
Use koa-___ to serve files from a directory as static assets with correct MIME types and caching headers.
koa-static (backed by koa-send) serves a directory tree over HTTP, sets Content-Type from the file extension, and supports maxAge, etag, and lastModified options.
Question 8
8
Which patterns are appropriate for running background jobs from a Koa app?
Select all that apply.
APush tasks to a queue (BullMQ, RabbitMQ) and process them in a separate worker processBUse setInterval inside a middleware for periodic tasksCRun a separate cron process that reads from the same databaseDSpawn child_process.fork() for CPU-intensive jobs
Queue-based workers, dedicated cron processes, and forked child processes are all valid patterns. setInterval inside middleware is brittle — it ties job scheduling to the HTTP process lifecycle and can block the event loop.