JS Promises

Question 1

Which queue do callbacks from promises go to when waiting to be being executed?

Answer 1

The microtasks queue

Question 2

How does these microtasks differ from the callbacks that enter the callback queue?

Answer 2

It has priority over the callback queue, meaning at the end of an event loop tick it’ll check the microtasks queue BEFORE running a task from the callback queue

Question 3

What happens if a microtask generates another during exectution?

Answer 3

That new microtask would be executed before any other callback (even if they are there waiting in the callback queue)

Question 4

Which arguments does a promise take?

Answer 4

Resolve & Reject

Question 5

How do you create a promise?

Answer 5

new Promise( (resolve, reject) => { } );

Question 6

What does calling resolve() mark the promise as?

Answer 6

Fulfilled

Question 7

What does calling reject() mark the promise as?

Answer 7

Rejected

Question 8

What state does the promise need to be in order to call .then() on it?

Answer 8

Resolved/Fulfilled

Question 9

What is resolve()?

Answer 9

A static method on the Promise constructor where we pass in the resolved value of the promise

Question 10

What is the different between passing in the resolved value like this: Promise.resolve(‘resolved value here’) as opposed to within a promise code block?

Answer 10

Promise.resolve(‘ ‘) will resolve the promise immediately.