useReducer and Complex State Quiz

Question 1

What does a reducer function receive and return?

Accepted Answer

The current state and an action, returning the next state

Answer

Props and children, returning JSX

Answer

An action and a dispatch, returning nothing

Answer

The previous props, returning a boolean

Question 2

Which situation most clearly calls for useReducer over useState?

Accepted Answer

Several state values that always change together in the same handlers

Answer

A single boolean toggle

Answer

A value read from a prop

Answer

A ref to a DOM node

Question 3

Why is this reducer case wrong?

Accepted Answer

It mutates the existing state instead of returning a new object

Answer

push is not allowed in JavaScript

Answer

The action type should be a string constant

Answer

It should return undefined

Question 4

Why should crypto.randomUUID() be called in the component rather than in the reducer?

Accepted Answer

It makes the reducer impure, producing different results for the same inputs

Answer

It is slower inside a reducer

Answer

Reducers cannot access browser APIs

Answer

It would generate invalid ids

Question 5

How should actions be named?

Accepted Answer

After what happened, such as submitted or deleted

Answer

After the field they set, such as setLoading

Answer

After the component that dispatched them

Answer

With numeric codes

Question 6

What is true of the dispatch function returned by useReducer?

Accepted Answer

It is stable for the life of the component, so it is safe to omit from dependency arrays

Answer

It changes identity on every render

Answer

It must be memoised with useCallback

Answer

It re-creates the reducer

Question 7

What problem do TanStack Query and SWR solve that a reducer does not?

Accepted Answer

Caching, refetching and deduplicating server data along with its loading and error states

Answer

Rendering lists efficiently

Answer

Type checking state

Answer

Styling components