Quiz for useMemo

Q1: What is the primary purpose of the useMemo hook?

A. To memoize expensive calculations B. To manage state C. To fetch data D. To handle events

Q2: When does useMemo recompute the memoized value?

A. Every render B. When a dependency changes C. Only on mount D. Never

Q3: How do you use useMemo?

A. const memoValue = useMemo(() => computeValue(), [deps]) B. const memoValue = useMemo(computeValue) C. const memoValue = useMemo() D. const memoValue = useMemo(() => {}, [])

Q4: What happens if you pass an empty dependency array to useMemo?

A. Memoized value is computed once on mount B. Value is recomputed every render C. Value never computed D. Throws error

Q5: What type of values can useMemo memoize?

A. Only primitives B. Only objects C. Any value or object returned from function D. Only arrays

Q6: Does useMemo guarantee the memoized value will never change?

A. Yes, always B. No, React may discard memoized value C. Yes, if dependencies don’t change D. No, it always changes

Q7: Can useMemo be used to memoize React components?

A. No B. Yes C. Only with useCallback D. Only with useState

Q8: What is the difference between useMemo and useCallback?

A. useMemo memoizes functions, useCallback memoizes values B. useMemo memoizes values, useCallback memoizes functions C. Both do the same D. useCallback is deprecated

Q9: What problem does useMemo solve?

A. Unnecessary expensive recalculations on renders B. State management C. Event handling D. Data fetching

Q10: When should you NOT use useMemo?

A. When calculations are cheap B. When you want to avoid re-renders C. When you want to cache API calls D. Always use useMemo

Q11: Can useMemo improve performance?

A. Yes, by avoiding recalculations B. No, it slows down rendering C. Yes, by skipping renders D. No, it caches state

Q12: How do you pass dependencies to useMemo?

A. As second argument array B. As first argument C. Inside the callback D. No dependencies needed

Q13: What does useMemo return?

A. A memoized value B. A function C. A promise D. A React element

Q14: Is useMemo a replacement for useState?

A. No B. Yes C. Only sometimes D. Yes, for memoized state

Q15: Which of these is a valid use case for useMemo?

A. Memoizing a complex calculation result B. Managing form input state C. Handling button clicks D. Fetching data

Q16: Can useMemo help reduce unnecessary renders?

A. Indirectly, by memoizing props passed down B. Directly, by preventing renders C. No D. Yes, always

Q17: What happens if dependencies in useMemo change?

A. Memoized value recalculates B. Component unmounts C. Memoized value is discarded forever D. Error is thrown

Q18: Can useMemo memoize functions?

A. Yes B. No C. Only with useCallback D. Only in class components

Q19: How does useMemo differ from React.memo?

A. useMemo memoizes values; React.memo memoizes components B. Both memoize components C. Both memoize values D. React.memo is deprecated

Q20: Does useMemo guarantee avoiding all expensive recalculations?

A. No, React may discard memoized results B. Yes, always C. Only in production D. Only in development