React Hooks Javascript 2

Question 1

What does the useState hook return?

Accepted Answer

An array with the state value and a setter function

Answer

useState returns a pair: the current state and a function to update it.

Question 2

Which hook lets you perform side effects in a function component?

Accepted Answer

useEffect

Answer

useEffect handles side effects such as data fetching and subscriptions.

Question 3

When does an effect with an empty dependency array `[]` run?

Accepted Answer

Only once after the initial mount

Answer

An empty dependency array runs the effect only once after the first render.

Question 4

What is the purpose of the cleanup function returned by useEffect?

Accepted Answer

To run before the component unmounts or before re-running the effect

Answer

The returned function cleans up subscriptions or timers before unmount or re-run.

Question 5

Which hook returns a mutable object whose `.current` persists across renders without causing re-renders?

Accepted Answer

useRef

Answer

useRef returns a mutable ref object that persists without triggering re-renders.

React Practice Test