React useEffect Hook MCQ useEffect Practice Questions

Direction: Choose the correct option

What is the useEffect hook used for?

A. Handling side effects in functional components

B. Creating refs

C. Optimizing renders

D. Managing state

Direction: Choose the correct option

By default, when does the effect function in useEffect run?

A. Only once after initial render

B. Only when dependencies change

C. Never

D. After every completed render (including first)

Direction: Choose the correct option

How do you make useEffect run only once (on mount)?

A. Pass an empty dependency array []

B. Use useMountEffect hook

C. Pass a non-empty array

D. Omit the second argument

Direction: Choose the correct option

What is the purpose of the cleanup function in useEffect?

A. To memoize values

B. To handle errors

C. To update state

D. To cancel subscriptions or timers before the component unmounts or before the next effect runs

Direction: Choose the correct option

Which of the following is a correct way to use useEffect for fetching data?

A. useEffect(() => { async function fetchData() { await ... }; fetchData(); }, []);

B. Both B and C

C. useEffect(async () => { await fetch(...); }, []);

D. useEffect(() => { fetch(...); }, []);

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