Streams & Performance — Series 3

Preview — 3 of 10 questions

What is logged?

javascript

const { Readable, Writable } = require('node:stream');
const { pipeline } = require('node:stream/promises');

const out = [];
await pipeline(
  Readable.from([1, 2, 3]),
  async function* (src) {
    for await (const n of src) yield n * 2;
  },
  new Writable({ objectMode: true, write(c, _e, cb) { out.push(c); cb(); } }),
);

console.log(out.join(','));

A1,2,3

BTypeError: generator is not a stream

C2,4,6

D6 — only the final value reaches the writable.

writable.write(chunk) returns false. What should the producer do?

AStop writing and wait for the 'drain' event before resuming — the false means the internal buffer is above highWaterMark, and ignoring it grows memory without bound.

BRetry immediately in a loop until it returns true.

CNothing — false means the chunk was rejected, so resend it.

DCall end(), since the stream is full.

What is logged? (CommonJS.)

javascript

const order = [];
setTimeout(() => order.push('timeout'), 0);
process.nextTick(() => order.push('nextTick'));
Promise.resolve().then(() => order.push('promise'));
order.push('sync');

setTimeout(() => console.log(order.join(' ')), 20);

Async promise nextTick timeout

BnextTick sync promise timeout

Csync timeout nextTick promise

Dsync nextTick promise timeout

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