What does useEffect(fn, []) do, and how is it different from useEffect(fn) with no dependency array? Answer in 2 to 3 sentences.

Write a Counter component using useState. Include increment, decrement, and a reset button that returns the count to the initial value.

Implement a useLocalStorage(key, initial) custom hook that mirrors useState but persists writes to window.localStorage. Handle the SSR case where window is undefined.

Refactor this counter from useState to useReducer. Why is useReducer a better fit once a component's state has multiple interrelated transitions?

The list below re-renders all 1000 rows whenever the parent rerenders, even though only query changes. Use useMemo and useCallback to fix it. Where is each hook actually doing work?

What are the two Rules of Hooks and why does React enforce them? Be specific about what breaks when you violate them.