Quiz: Async JavaScript

5 questionsNo time limitPass: 60%+10 XP on first pass

Why JavaScript doesn't freeze while waiting, the event loop as a picture, callbacks vs promises vs async/await, error handling, Promise.all and calling APIs with fetch.

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Question 1

In what order does this print the letters?

setTimeout(() => console.log("A"), 0);
Promise.resolve().then(() => console.log("B"));
console.log("C");

C B AA B CC A BB C A

Question 2
What does an async function always return?
undefinedA PromiseThe value directlyA callback
Question 3
fetch() to a URL that returns HTTP 404. What happens?
The promise rejectsThe promise resolves; you must check res.okThe browser crashesIt retries automatically
Question 4
Which runs three independent requests in parallel and waits for all?
await a; await b; await c;await Promise.all([a, b, c])Promise.race([a, b, c])setTimeout(a, b, c)

Question 5

What does this print?

async function f() { return 5; }
f().then((v) => console.log(v + 1));

56[object Promise]1undefined