Redux selectors in React Native - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Redux selector?

A Redux selector is a function that extracts specific data from the Redux store state. It helps components get only the data they need.

beginner

Why use selectors instead of accessing state directly in components?

Selectors keep components simple, improve code reuse, and can optimize performance by memoizing data to avoid unnecessary re-renders.

intermediate

What is memoization in the context of Redux selectors?

Memoization means caching the result of a selector so if the input state hasn't changed, the selector returns the cached result, improving performance.

intermediate

How do you create a memoized selector using Reselect?

Use the createSelector function from the Reselect library. It takes input selectors and a result function, returning a memoized selector.

beginner

Give an example of a simple selector function.

Example: const selectUserName = state => state.user.name; This selector returns the user's name from the state.

What does a Redux selector do?

A Extracts specific data from the Redux store state

B Dispatches actions to update the store

C Creates the Redux store

D Defines reducers

Selectors are functions that pick specific pieces of data from the Redux state.

Which library is commonly used to create memoized selectors?

A React Router

B Redux Thunk

C Reselect

D Axios

Reselect provides createSelector to build memoized selectors.

Why is memoization useful in selectors?

A It caches results to avoid recalculating when state hasn't changed

B It makes the store bigger

C It dispatches actions faster

D It changes the state directly

Memoization improves performance by returning cached results if inputs are unchanged.

How do selectors help components?

A By managing network requests

B By handling user input events

C By styling the UI

D By providing only the data components need

Selectors simplify components by giving them just the data they require.

What is the input to a selector function?

A An action object

B The Redux store state

C A React component

D A reducer function

Selectors receive the Redux state as input to extract data.

Explain what a Redux selector is and why it is useful in a React Native app.

Think about how components get data from the store.

Describe how memoization works in Redux selectors and its benefits.

Consider what happens when state does not change.