Write a usePrevious hook.

• Returns undefined on the first render
• After a re-render caused by a changed value, returns the value from the render before
• Stores the value in a useRef, not useState, so the hook never triggers an extra render
• Updates the ref in an effect (useEffect), after the render, so the returned value is still the old one during the render
• Works for any value type: numbers, strings, objects and arrays are returned by reference
• Demo shows current and previous count and updates correctly on each click

Only after every requirement works.

• Variant that returns the last value that was different from the current one, so unrelated re-renders do not make previous === current
• Type the hook as usePrevious<T>(value: T): T | undefined
• Explain what you would see in React Strict Mode in development and why the hook still works