useCallback optimization in React Native - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of useCallback in React Native?

useCallback helps remember a function so it doesn’t get recreated on every render. This saves work and can make your app faster.

beginner

When should you use useCallback?

Use it when you pass functions to child components that depend on props or state, to avoid unnecessary re-renders.

intermediate

What happens if you forget to add dependencies in useCallback?

The function may use old values and cause bugs because it won’t update when those values change.

intermediate

How does useCallback help with React Native's FlatList performance?

By memoizing item render functions, useCallback prevents unnecessary re-renders of list items, making scrolling smoother.

advanced

Can useCallback always improve performance?

No. If the function is simple or not passed to children, useCallback might add extra work and slow things down.

What does useCallback return?

A A state variable

B A new component

C A memoized version of the callback function

D A side effect

useCallback returns a memoized function that only changes if its dependencies change.

Which of these is a correct use of useCallback?

A const memoFn = useCallback(() => doSomething(), [dependency]);

B const memoFn = useCallback(doSomething());

C const memoFn = useCallback(doSomething, []);

D const memoFn = useCallback(() => doSomething());

You must pass a function and a dependency array to useCallback. Option A is correct.

What is a common mistake when using useCallback?

A Not including dependencies in the array

B Using it for state variables

C Calling it inside loops

D Returning JSX from it

Forgetting dependencies causes stale closures and bugs.

How does useCallback help child components?

A Makes them load faster

B Prevents them from re-rendering if props don’t change

C Changes their state automatically

D Removes them from the UI

Memoized functions keep props stable, so children skip re-rendering.

When might useCallback hurt performance?

A When used with state setters

B When used with many dependencies

C When used inside <code>useEffect</code>

D When used on simple functions that don’t change

Memoizing simple functions can add overhead without benefit.

Explain how useCallback helps optimize React Native apps.

Think about how functions passed to children can cause extra work.

Describe common mistakes when using useCallback and their effects.

What happens if the function uses old values?