The Hooks Library — Chapter Quiz

Question 1

1

Where can you legally call a hook?

AAnywhere — hooks are just functionsBTop level of a component or another hookCInside an event handlerDInside an if to skip it conditionally

Rules of hooks: top level only, from a component or another hook. The order has to be identical every render.

Question 2

2

Mutating ref.current triggers a re-render.

TTrueFFalse

Refs are mutable but NOT reactive. Use state for values that should drive the UI; use refs for internal bookkeeping.

Question 3

3

What does useMemo(fn, deps) do?

ARuns fn after every renderBCaches fn's return value; only recomputes when deps changeCMemoizes a componentDMakes a function stable across renders

useMemo is a cache. useCallback is the function-identity equivalent. memo (no use) wraps components.

Question 4

4

When is useCallback actually useful?

AAlways — every function should be wrappedBWhen the function is in another hook's deps, or passed to a memo'd childCOnly inside event handlersDOnly for functions that take many arguments

The wins come from stable identity for deps and memo. For a plain DOM <button onClick={fn}> it doesn't matter.

Question 5

5

Two components want to share the same theme value. Which is the right tool?

AProp-drill it through every layerBPut it in a global letCuseContext with a ProviderDSave it to localStorage

Context is built for "many components, scattered, same value". Wrap with a custom useTheme() hook for ergonomics.

Question 6

6

A custom hook is named…

AAnything, as long as it returns stateBStarts with useCStarts with withDHas a .hook.js suffix

The use prefix is required so the linter can check the rules of hooks.

Question 7

7

Two components calling useOnlineStatus() share the same state.

TTrueFFalse

Custom hooks share CODE, not STATE. Each component instance gets its own state.

Question 8

8

For complex state logic with many transitions, the upgrade from useState is _________.

A reducer lets you keep all state transitions in one pure function, which is easier to test and reason about.

Test what you learned.