Question 1

What is Redux and what problem does it solve?

Accepted Answer

Redux is a predictable state container for JavaScript apps. It solves the problem of managing complex application state by providing a single source of truth, making state changes predictable through pure reducer functions.

Question 2

What are the three core principles of Redux?

Accepted Answer

The three principles are: 1) Single source of truth - the entire app state is stored in one object tree. 2) State is read-only - changes happen only via dispatched actions. 3) Changes are made with pure functions called reducers.

Question 3

What is the difference between Redux and React Context API?

Accepted Answer

Redux provides predictable state updates, middleware for side effects, DevTools for debugging, and efficient re-renders via selectors. Context API is simpler but causes all consumers to re-render on any state change.

Question 4

What is Redux Toolkit and why was it created?

Accepted Answer

Redux Toolkit is the official toolset for efficient Redux development. It was created to simplify Redux setup, reduce boilerplate, include best practices by default, and provide utilities like createSlice and createAsyncThunk.

Question 5

What is a reducer and what rules must it follow?

Accepted Answer

A reducer is a pure function that takes current state and an action, returning a new state. It must be pure (no side effects), never mutate state directly, and always return a new state object for changes.

Question 6

What is createSlice in Redux Toolkit?

Accepted Answer

createSlice is a function that generates action creators and action types automatically based on reducer functions you define. It uses Immer internally, allowing you to write mutating logic that produces immutable updates.

Question 7

What is the difference between useSelector and connect()?

Accepted Answer

useSelector is a React hook that extracts data from the Redux store using a selector function. connect() is a higher-order component that wraps your component. Hooks are simpler and more readable; connect() offers more optimization options.

Question 8

What is Redux Thunk and how does it work?

Accepted Answer

Redux Thunk is middleware that allows action creators to return functions instead of action objects. These functions receive dispatch and getState, enabling async operations like API calls before dispatching actions.

Question 9

What is state normalization in Redux?

Accepted Answer

State normalization means storing data in a flat structure with entities keyed by ID, similar to database tables. This eliminates data duplication, simplifies updates, and prevents inconsistencies in nested data.

Question 10

What is a memoized selector and when should you use one?

Accepted Answer

A memoized selector caches its result and only recalculates when input selectors change. Use them when deriving data from state (filtering, sorting) to prevent expensive recalculations on every render.

Question 11

What is createAsyncThunk in Redux Toolkit?

Accepted Answer

createAsyncThunk is a function that generates thunks handling async request lifecycles. It automatically dispatches pending, fulfilled, and rejected actions, simplifying API call handling and loading states.

Question 12

How do you prevent unnecessary re-renders with useSelector?

Accepted Answer

Select only the specific data needed, not entire state slices. Use shallow equality checks for objects/arrays, memoize selectors with createSelector, and split components to subscribe to different state pieces.

Question 13

What is middleware in Redux?

Accepted Answer

Middleware extends Redux with custom functionality between dispatching an action and it reaching the reducer. Common uses include logging, crash reporting, async operations, and routing.

Question 14

When should you NOT use Redux?

Accepted Answer

Avoid Redux for simple apps with minimal shared state, apps where state doesn't change much, or when React's built-in useState/useContext suffices. Redux adds complexity that isn't always justified.

Question 15

What is Redux DevTools?

Accepted Answer

Redux DevTools is a browser extension for debugging Redux apps. It provides time-travel debugging, action history, state inspection, and the ability to replay actions—essential for development and debugging.

Redux Fundamentals(7 questions)

What is Redux and what problem does it solve?

What are the three core principles of Redux?

What is a Redux store and what methods does it provide?

What is an action in Redux?

What is a reducer and what rules must it follow?

What does it mean for a reducer to be a "pure function"?

What is the Redux data flow and how does it work?

Redux vs Alternatives(4 questions)

What is the difference between Redux and Context API?

When should you use Redux vs React Context?

What is the difference between Redux and Zustand?

When should you NOT use Redux?

Actions and Reducers(5 questions)

What is an action creator and why would you use one?

How do you handle initial state in a reducer?

What is reducer composition and why is it important?

How do you update nested state immutably in a reducer?

What is the purpose of combineReducers?

React-Redux Integration(6 questions)

What is React-Redux and why do you need it?

What is the Provider component and how does it work?

What are the useSelector and useDispatch hooks?

How do you prevent unnecessary re-renders with useSelector?

What is the difference between useSelector and connect()?

What is mapStateToProps and mapDispatchToProps?

Redux Toolkit(6 questions)

What is Redux Toolkit and why was it created?

What is createSlice and how does it simplify Redux?

How does Immer work in Redux Toolkit?

What is createAsyncThunk and how do you use it?

What is configureStore and how does it differ from createStore?

What is createEntityAdapter and when would you use it?

Middleware(4 questions)

What is middleware in Redux and how does it work?

What is Redux Thunk and how does it work?

What is Redux Saga and how does it differ from Thunk?

How do you write custom middleware?

Async Operations(4 questions)

How do you handle asynchronous operations in Redux?

What is the loading/success/error pattern for async actions?

How do you handle API calls in Redux?

What is optimistic updating and how do you implement it?

Selectors(4 questions)

What is a selector in Redux?

What is Reselect and why would you use it?

What is a memoized selector and when should you use one?

How do you create selectors with createSelector?

State Management(4 questions)

What is state normalization and why is it important?

How do you normalize nested data in Redux?

What should and shouldn't be stored in Redux state?

How do you persist Redux state to localStorage?

Performance and Testing(5 questions)

What causes unnecessary re-renders in Redux applications?

How do you optimize selector performance?

How do you test Redux reducers?

How do you test async thunks?

What is Redux DevTools and how do you use it?