React Hooks useCallback Hook

Question 1

What does the useCallback hook primarily do in React?

Accepted Answer

It memoizes a callback function so it only changes if its dependencies change

Answer

It automatically calls a function every render

Answer

It replaces the need for event handlers in functional components

Answer

It creates a new function on every render for performance

Question 2

What is the correct syntax for using useCallback?

Accepted Answer

useCallback(fn, [deps])

Answer

useCallback(fn)

Answer

useCallback([deps], fn)

Answer

useCallback(fn, deps, options)

Question 3

When is it most beneficial to use useCallback?

Accepted Answer

When passing a callback function as a prop to a child component wrapped in React.memo

Answer

When you want to run a function immediately on mount

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When you need to access the DOM directly

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When replacing useState for complex state logic

Question 4

What happens if you pass an empty dependency array [] to useCallback?

Accepted Answer

The callback is memoized once and never changes

Answer

The callback is recreated on every render

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The callback is never called

Answer

useCallback throws an error

Question 5

What is the key difference between useCallback and useMemo?

Accepted Answer

useCallback memoizes a function itself; useMemo memoizes the return value of a function

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useCallback is for class components; useMemo is for functional components

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useCallback can only handle async functions; useMemo handles sync functions

Answer

There is no difference; they are interchangeable

Question 6

Which of the following is a common problem that useCallback helps solve?

Accepted Answer

Unnecessary re-renders of child components due to new function references on each render

Answer

Memory leaks from asynchronous operations

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Stale state values inside event handlers

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Blocking the main thread during expensive computations

Question 7

What is a 'stale closure' problem in the context of useCallback?

Accepted Answer

When a memoized callback captures outdated values from a previous render because dependencies were omitted

Answer

A callback that is never garbage collected

Answer

When useCallback is called inside a loop or condition

Answer

A callback that executes after the component unmounts