React Hooks Javascript 3

Question 1

What does useMemo do?

Accepted Answer

Memoizes a computed value to avoid recalculating on every render

Answer

useMemo caches an expensive computed value, recomputing only when dependencies change.

Question 2

What does useCallback return?

Accepted Answer

A memoized version of the callback function

Answer

useCallback returns a memoized callback that only changes when dependencies change.

Question 3

Which hook subscribes a component to a React context value?

Accepted Answer

useContext

Answer

useContext reads the current value of a context within a component.

Question 4

What happens if you omit the dependency array entirely in useEffect?

Accepted Answer

It runs after every render

Answer

Without a dependency array, the effect runs after every render.

Question 5

Why might updating state inside useEffect without dependencies cause an infinite loop?

Accepted Answer

Each state update re-renders, which re-runs the effect, updating state again

Answer

The render-update-render cycle repeats endlessly without proper dependencies.

React Practice Test