React Hooks 2

Question 1

What does the useReducer hook return?

Accepted Answer

The current state and a dispatch function

Answer

useReducer returns an array containing the current state and a dispatch function to trigger state updates.

Question 2

When does the function passed to useEffect run if the dependency array is empty?

Accepted Answer

Only once after the initial render

Answer

An empty dependency array means the effect runs only once after the initial render, similar to componentDidMount.

Question 3

What is the purpose of the useRef hook?

Accepted Answer

To persist a mutable value across renders without causing re-renders

Answer

useRef returns a mutable ref object whose .current property persists across renders and does not cause re-renders when changed.

Question 4

Which hook would you use to read a context value in a function component?

Accepted Answer

useContext

Answer

useContext accepts a context object and returns the current context value for that context.

Question 5

What does useMemo return?

Accepted Answer

A memoized value recomputed only when dependencies change

Answer

useMemo returns a memoized value that is recomputed only when one of its dependencies changes.

React Practice Test