Chapter quiz · Async, Modules & Errors

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8 questions on Async, Modules & Errors. Pass 70% to clear the chapter.

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Quiz

Async, Modules & Errors — Chapter Quiz

Eight questions on modules, promises, async/await, fetch, errors, and iterators.

0/ 8

Question 1
1
How many default exports can a single ES module have?
AZeroBExactly oneCAs many as you wantDOne per type (one class, one function, etc.)
A module can have at most one export default. Named exports have no limit.
Question 2
2
What does this code log (eventually)?
```
Promise.resolve(1)
  .then(n => n + 1)
  .then(n => n * 10)
  .then(console.log);
```
A1B10C20D11
1 → +1 → 2 → *10 → 20. Each .then returns the next promise resolving to whatever its callback returned.
Question 3
3
A fetch() call rejects when the server returns a 404.
TTrueFFalse
fetch only rejects on network failure. 404, 500, and other HTTP error codes still RESOLVE — you have to check res.ok yourself.
Question 4
4
Inside an async function, what does await somePromise do?
APauses the function and returns the resolved valueBBlocks the entire program until the promise settlesCConverts the promise into a synchronous callDSchedules a callback for later
await pauses ONLY this async function — the rest of the program keeps running. When the promise settles, the function resumes with the resolved value (or the rejection becomes a throw inside the function).
Question 5
5
Which is the right way to run two async calls in parallel and wait for both?
Aawait a(); await b();Bconst [x, y] = await Promise.all([a(), b()]);CPromise.race([a(), b()])DYou can only run them sequentially
Promise.all runs concurrently and resolves with both values. Option a runs them SEQUENTIALLY (slower). Option c gives the first to settle, not both.
Question 6
6
What is logged?
```
try {
  null.x;
} catch (e) {
  console.log(e.name);
}
```
A"Error"B"TypeError"C"ReferenceError"D"SyntaxError"
Reading a property of null or undefined throws a TypeError. The runtime picks the most specific built-in subclass.
Question 7
7
A generator function (function*) returns an iterator that you can use with for..of.
TTrueFFalse
Generators return an iterator that's also iterable. You can for..of over them, spread them, or call Array.from(...).
Question 8
8
To consume an async iterable (one yielding promises), use for ____ (const x of stream) { ... }.
for await..of waits for each promise to resolve before moving to the next item — used for streams, paginated APIs, and async generators.