State with useState Quiz

Question 1

Why can a plain local variable not hold values that change over time?

Accepted Answer

Changing it does not trigger a re-render, and it is reinitialised on the next render

Answer

Variables are read only inside components

Answer

React forbids let inside components

Answer

Variables cannot hold numbers in JSX

Question 2

What does count log here after one click?

Accepted Answer

0

Answer

1

Answer

undefined

Answer

It throws an error

Question 3

Starting from 0, what is count after this handler runs?

Accepted Answer

1

Answer

3

Answer

0

Answer

2

Question 4

When should you use the updater form of a setter?

Accepted Answer

Whenever the new value is computed from the previous one

Answer

Only inside effects

Answer

Only when the state is an object

Answer

Never, it is deprecated

Question 5

Why does this fail to update the screen?

Accepted Answer

The array is mutated so its reference is unchanged, and React sees no new state

Answer

push is not a function on state arrays

Answer

setTags must be called twice

Answer

Arrays cannot be stored in state

Question 6

Which of these should NOT be stored in state?

Accepted Answer

A total that can be calculated from the list of items

Answer

The list of items a user has added

Answer

The current value of a text input

Answer

Whether a dialog is open

Question 7

Two sibling components need the same value. What should you do?

Accepted Answer

Lift the state to their closest common parent and pass it down

Answer

Duplicate the state in both components

Answer

Store it in a module level variable

Answer

Pass state upward through a prop