React Hooks useContext and useReducer 3

Question 1

Which hook do you use inside a component to read a context value?

Accepted Answer

useContext

Answer

The useContext hook is the built-in React hook for reading a context value inside a function component.

Question 2

How do you update context value from a child component?

Accepted Answer

Provide a setter or dispatch function as part of the context value

Answer

Including an updater function (setState or dispatch) in the context value allows consumers to trigger changes.

Question 3

What performance optimization prevents context consumers from re-rendering when unrelated state changes in the Provider?

Accepted Answer

Memoizing the context value with useMemo

Answer

Wrapping the context value in useMemo ensures the same reference is passed unless the actual data changes.

Question 4

What is the immer library often used for with useReducer?

Accepted Answer

Writing reducers with mutable syntax that produce immutable state

Answer

Immer lets you write reducer logic as if you are mutating state, while actually producing a new immutable state.

Question 5

Can you call dispatch from inside a useEffect?

Accepted Answer

Yes, and dispatch is stable so it won't need to be in the dependency array

Answer

React guarantees dispatch identity is stable across renders, so it does not need to be listed as a dependency.

React Practice Test