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8 questions on Async in Node. Pass 70% to clear the chapter.

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Async in Node — Chapter Quiz

Eight questions on the event loop, promises, workers, timers.

0/ 8

Question 1
1
How many threads run your JavaScript by default in Node?
AOneBOne per CPU coreCOne per requestDUnlimited
Node runs JS on a single thread by default. Worker threads or child processes give you more.
Question 2
2
Promise .then callbacks (microtasks) run before the next setTimeout callback.
TTrueFFalse
Microtasks (promise then, queueMicrotask) flush between event loop phases — before the next timer or IO callback.
Question 3
3
How do you cancel an in-flight fetch?
ACall fetch.cancel()BPass an AbortSignal and call controller.abort()CThrow inside the handlerDYou cannot cancel fetch
AbortController/AbortSignal is the standard cancellation mechanism. Pass signal to fetch, call abort() to cancel.
Question 4
4
Which is best for CPU-heavy work?
AA loop in the main threadBA worker threadCA setTimeout chainDA microtask
Worker threads run in a separate thread — main event loop stays responsive. Don't block the main thread for CPU work.
Question 5
5
What does this code print?
```
console.log("1");
Promise.resolve().then(() => console.log("2"));
setTimeout(() => console.log("3"), 0);
console.log("4");
```
A1, 2, 3, 4B1, 4, 2, 3C1, 3, 2, 4D4, 1, 2, 3
Synchronous lines first (1, 4). Then microtasks (2). Then the timer (3). Microtasks beat macrotasks.
Question 6
6
The promise-based version of setTimeout lives in node:timers/___.
node:timers/promises exposes setTimeout, setInterval, setImmediate that return promises.
Question 7
7
What's setImmediate(fn)'s difference from setTimeout(fn, 0)?
ANo differenceBsetImmediate runs in a specific event loop phase, after IOCsetImmediate runs synchronouslyDsetImmediate is faster but less reliable
setImmediate is defined to run in the "check" phase. More predictable than setTimeout(fn, 0) for "run next tick" needs.
Question 8
8
What is the BEST way to convert a callback-style API to promises?
Autil.promisify(fn)Bnew Promise((resolve, reject) => fn(...))CBoth — but built-in /promises namespaces are best where they existDUse callbacks forever
For Node std-lib, prefer /promises namespaces (e.g. node:fs/promises). For third-party callback APIs, promisify is the canonical bridge.