React Hooks useRef and useMemo

Question 1

What does useRef return?

Accepted Answer

A mutable ref object with a .current property

Answer

A state value and setter

Answer

A memoized value

Answer

A DOM element directly

Question 2

Does mutating a ref's .current property cause a re-render?

Accepted Answer

No, mutations to ref.current do not trigger re-renders

Answer

Yes, always

Answer

Only if the ref is connected to a DOM element

Answer

Yes, but only in StrictMode

Question 3

How do you attach a ref to a DOM element?

Accepted Answer

Pass it as the ref prop on the JSX element

Answer

Pass it as a prop called innerRef

Answer

Call useRef(element)

Answer

Assign it in useEffect

Question 4

What is useMemo used for?

Accepted Answer

Memoizing expensive computed values between renders

Answer

Storing DOM references

Answer

Triggering side effects

Answer

Managing async state

Question 5

What are the two arguments to useMemo?

Accepted Answer

A factory function and a dependency array

Answer

A value and a default

Answer

A ref and a callback

Answer

An initial value and a reducer

Question 6

When does useMemo recompute its value?

Accepted Answer

When one or more items in the dependency array change

Answer

On every render

Answer

Never after the first render

Answer

When the parent re-renders only