React REACT 2

Question 1

What does the useEffect cleanup function run before?

Accepted Answer

Before the next effect re-runs and on unmount

Answer

Only on initial mount

Answer

After every render unconditionally

Answer

Only when state is reset

Question 2

Which hook should you use to memoize an expensive computed value?

Accepted Answer

useMemo

Answer

useCallback

Answer

useRef

Answer

useReducer

Question 3

What is the purpose of the key prop when rendering a list?

Accepted Answer

Help React identify which items changed, added, or removed

Answer

Style each list item uniquely

Answer

Set the order numerically

Answer

Bind event handlers automatically

Question 4

Why is using an array index as a key often discouraged?

Accepted Answer

It can cause incorrect state when the list reorders

Answer

It is slower to compute

Answer

React forbids numeric keys

Answer

It breaks TypeScript typing

Question 5

What does useCallback return?

Accepted Answer

A memoized version of the callback function

Answer

A cached computed value

Answer

A ref object

Answer

A new component instance

Question 6

In React, what is a controlled component?

Accepted Answer

A form input whose value is driven by React state

Answer

A component wrapped in memo

Answer

A class component with refs

Answer

A component rendered by a portal

Question 7

What hook lets you access a DOM node directly?

Accepted Answer

useRef

Answer

useState

Answer

useContext

Answer

useMemo