Top 20+ Redux Interview Questions and Answers

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Redux is a JavaScript library used for managing application state, especially in React apps. It was created in 2015 by Dan Abramov and Andrew Clark, inspired by Facebook’s Flux architecture. Redux simplifies state tracking and management in complex apps by storing all state in a single location. If you are preparing for a front-end developer role, Redux often comes up in interviews. To help you get ready, we have compiled 20+ important Redux interview questions and answers – covering basics to advanced topics. 

Fun Fact – Redux was originally created as a live-coding demo and wasn’t meant to become this popular – but developers loved its simplicity and power.

Note – We have grouped the most commonly asked Redux interview questions into three levels – basic, intermediate, and advanced, for quick and easy reference. 

Basic Level Redux Interview Questions for Freshers

Here is a list of commonly asked Redux interview questions and answers to help freshers build a strong foundation in state management.

1. What is Redux and why is it used?

Redux is a state management library for JavaScript applications. It helps store and manage app-wide state in one place. It is often used with React but works with any UI layer.

2. What are the core principles of Redux?

Redux is based on three key ideas:

• Single source of truth – The entire app state lives in one object.
• State is read-only – You can’t change state directly.
• Changes are made with pure functions – Reducers return a new state based on actions.

3. Explain the role of actions in Redux.

Actions describe what happened. They are plain JavaScript objects with a type field and optional data. They tell reducers how to update the state.

4. What is a reducer in Redux?

A reducer is a pure function. It takes the current state and an action, then returns a new state. It never mutates the original state.

5. How does Redux differ from React’s built-in state?

React state is local to components. Redux state is global and managed outside of components. Redux works well for complex apps where many components need shared data.

6. What is the purpose of the Redux store?

The store holds the entire app state. It allows components to read state, dispatch actions, and subscribe to changes.

7. How do you update state in Redux?

You dispatch an action. That action goes to the reducer. The reducer returns a new state, which replaces the old one.

Intermediate Level Redux Interview Questions

These are intermediate-level Redux interview questions and answers that test your practical knowledge.

8. How does middleware work in Redux?

Middleware sits between dispatching an action and the moment it reaches the reducer. It can stop, change, delay, or log actions. It’s often used for async logic, like API calls.

9. What is the role of combineReducers in Redux?

combineReducers is a helper function. It lets you split the state and reducer logic into smaller pieces. Each reducer handles a part of the overall state tree.

10. How do you handle side effects in Redux?

You use middleware like Redux Thunk, Redux Saga, or RTK Query. These tools help manage tasks like fetching data, logging, or delaying actions without blocking the main flow.

11. Explain the useSelector and useDispatch hooks in React-Redux.

useSelector lets a component read state from the Redux store. You pass a function to pick the needed part of the state.

useDispatch gives access to dispatch so you can send actions. I use both hooks in function components instead of connect.

12. What is immutability and why is it important in Redux?

Immutability means not changing the original state object. In Redux, every state update returns a new object. This helps with debugging, tracking changes, and performance with shallow comparisons.

13. How do you debug a Redux application?

I use Redux DevTools. It shows state, actions, and time-travel debugging. I can replay actions, view diffs, and check if a reducer is behaving as expected. Console logs also help sometimes.

14. What is the difference between mapStateToProps and mapDispatchToProps?

Both are used with the connect function in older Redux setups.
mapStateToProps pulls state data and passes it as props.
mapDispatchToProps allows dispatching actions as props.
Today, I prefer hooks like useSelector and useDispatch for cleaner code in functional components.

Advanced Level Redux Interview Questions for Experienced Professionals 

Let’s go through some advanced-level interview questions on Redux for experienced candidates. 

15. How would you optimize performance in a large Redux app?

I focus on reducing unnecessary re-renders. I use React.memo, avoid deep props, and split reducers. I also use Reselect to memoize derived data. Keeping components connected only to the data they need helps a lot.

16. What are some common anti-patterns in Redux and how do you avoid them?

One common mistake is putting too much logic in reducers. Reducers should stay pure. Another is dispatching actions from inside reducers, which breaks Redux rules. I also avoid deeply nested state unless absolutely needed. Keeping actions and state simple makes debugging easier.

17. How can Redux be used in a server-side rendered (SSR) React app?

Redux works well with SSR by creating a fresh store on every request. The server fetches data, fills the store, and passes the state to the client. On the client side, Redux hydrates the app using that state. Libraries like Next.js handle most of the setup.

18. What is Reselect and how does it help with performance?

Reselect is a library for writing memoized selectors. A selector computes derived data from the state. If the inputs don’t change, the output stays cached. This avoids re-running expensive calculations and helps prevent unnecessary renders.

19. How would you implement undo/redo functionality in Redux?

I wrap the reducer in a higher-order reducer. This wrapper tracks past, present, and future states. Actions like UNDO or REDO shift the state pointer. Libraries like redux-undo offer ready solutions, but I prefer writing a simple custom one when possible.

20. How do you manage deeply nested state structures in Redux?

I normalize the state using flat structures. Tools like Normalizr help with this. I keep IDs in arrays and store entities in objects by ID. This makes updates easier and selectors faster. I also split the state by domain to keep things clean.

Other Important Redux Interview Questions

Here are some extra Redux interview questions and answers that are often asked to test your overall grasp of Redux in different scenarios.

React and Redux Interview Questions

1. How does React context compare to Redux?
2. How do you connect a React component to Redux?
3. How do React hooks simplify using Redux in functional components?
4. How do you structure a React-Redux project?
5. What are the benefits of using Redux with React?

Redux JS Interview Questions

1. What is the difference between Redux and Flux?
2. How do you test Redux actions and reducers?
3. What are action creators in Redux?
4. Can Redux be used without React?
5. What is the role of applyMiddleware in Redux?

ReactJS and Redux Interview Questions 

This section covers common ReactJS Redux interview questions to help you understand how these two libraries work together in real-world applications.

1. How does Redux help manage state in React applications?
2. What is the difference between useState and Redux state?
3. How do you pass props from Redux to React components?
4. How does Redux improve maintainability in large React projects?
5. What are the common performance bottlenecks in React-Redux apps?

Redux Toolkit Interview Questions

1. What is Redux Toolkit and why is it recommended?
2. How does createSlice simplify Redux code?
3. What is the use of configureStore in Redux Toolkit?
4. How do you handle asynchronous logic in Redux Toolkit?
5. What are the benefits of using Redux Toolkit over plain Redux?

Redux Saga Interview Questions

1. What is Redux Saga and how does it work?
2. What is the difference between Redux Saga and Redux Thunk?
3. How does the yield keyword work in Redux Saga?
4. What are watchers and workers in Redux Saga?
5. How do you cancel a running saga?

Redux Thunk Interview Questions

1. What is Redux Thunk used for?
2. How do you write an async action using Redux Thunk?
3. What are the pros and cons of using Redux Thunk?
4. How do you test a Redux Thunk function?
5. Can you dispatch multiple actions from a single thunk?

Tips to Prepare for Redux Interview

Preparing for a Redux interview requires clarity, hands-on practice, and knowing how Redux fits real-world apps. Here are some simple, helpful tips to get ready.

• Understand Redux basics well: Be clear on actions, reducers, and the store. Interviewers often start here.
• Practice writing reducers: Reducers must be pure and return to a new state. Try writing a few by hand.
• Know when to use Redux: Be ready to explain why and when Redux is useful (and when it’s not).
• Get hands-on with Redux Toolkit: It is the standard now. Use createSlice, configureStore, and createAsyncThunk.
• Work on a small project: Build a to-do app or blog app using Redux to get comfortable with the flow.
• Use DevTools: Learn how to track actions, debug state, and time-travel in Redux DevTools.
• Read real code: Browse GitHub projects to see how teams structure Redux code.
• Practice explaining concepts: Try teaching a Redux topic to someone else or write it down simply.

Wrapping Up

With these Redux interview questions and answers, you now have a solid foundation to face both basic and advanced technical rounds with confidence. 

If you are ready to take the next step in your tech career, check out Hirist. It is a leading job portal made especially for tech professionals. Whether you are just starting your career or already experienced, Hirist helps you find the best Redux jobs in India.

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