React Advanced Topics 2

Question 1

What is the primary purpose of React.memo?

Accepted Answer

To prevent a function component from re-rendering when its props are unchanged

Answer

React.memo is a higher-order component that skips re-rendering when props are shallowly equal.

Question 2

What does the useCallback hook return?

Accepted Answer

A memoized version of the callback function

Answer

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

Question 3

When should you use useMemo?

Accepted Answer

To memoize an expensive computed value between renders

Answer

useMemo caches a computed value so it is only recalculated when dependencies change.

Question 4

What is the purpose of the key prop when rendering lists?

Accepted Answer

To help React identify which items changed, added, or removed

Answer

Keys give elements a stable identity so React can efficiently reconcile list changes.

Question 5

What problem does the useRef hook commonly solve?

Accepted Answer

Holding a mutable value that persists without causing re-renders

Answer

useRef returns a mutable object whose .current persists across renders without triggering re-renders.

React Practice Test