React Hooks useContext and useReducer 2

Question 1

What is the third argument to useReducer used for?

Accepted Answer

Lazy initialization of state via an init function

Answer

The optional third argument is an init function called with the second argument to lazily initialize state.

Question 2

How does React compare Provider values to decide if consumers re-render?

Accepted Answer

Object.is (reference equality)

Answer

React uses Object.is to compare old and new context values, so new object literals always trigger re-renders.

Question 3

Which pattern combines useContext and useReducer to mimic a Redux-like store?

Accepted Answer

Storing state and dispatch in a context Provider

Answer

Placing useReducer's state and dispatch into Context lets any descendant read and update shared state without prop drilling.

Question 4

What happens if no Provider wraps a component that calls useContext?

Accepted Answer

The hook returns the default value passed to createContext

Answer

If no Provider is found, useContext returns the default value specified when the context was created.

Question 5

In a useReducer action, what property typically identifies the type of state change?

Accepted Answer

action.type

Answer

By convention, actions have a type string that the reducer uses to determine which state transition to perform.

React Practice Test