JavaScript Async Programming 2

Question 1

What does the `Promise.allSettled()` method return?

Accepted Answer

A promise that resolves with an array of outcome objects for all promises

Answer

`Promise.allSettled()` waits for all promises to settle (either fulfill or reject) and returns a promise that resolves with an array of objects, each describing the outcome with a `status` property of `'fulfilled'` or `'rejected'`.

Question 2

Which keyword is used to pause execution inside an async function until a promise resolves?

Accepted Answer

await

Answer

The `await` keyword is used inside `async` functions to pause execution until the awaited promise resolves or rejects, making asynchronous code look and behave like synchronous code.

Question 3

What is the output of: `console.log(1); setTimeout(() => console.log(2), 0); console.log(3);`?

Accepted Answer

1, 3, 2

Answer

Synchronous code runs first: `1` and `3` are logged immediately. The `setTimeout` callback is placed in the macrotask queue and runs after the call stack is empty, so `2` is logged last.

Question 4

What does `Promise.race()` return?

Accepted Answer

A promise that resolves or rejects with the value of the first settled promise

Answer

`Promise.race()` returns a promise that settles (resolves or rejects) as soon as the first input promise settles, adopting its value or reason.

Question 5

How do you handle errors in async/await code?

Accepted Answer

Using try/catch blocks inside the async function

Answer

You can wrap `await` expressions in `try/catch` blocks to handle rejected promises. You can also chain `.catch()` on the returned promise, but try/catch is the idiomatic approach inside async functions.

JavaScript Practice Test

JavaScript Practice Test

JavaScript Async Programming 2