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All Interviews

Top 50 React Interview Questions and Answers

17/Sep/2021 | 8 minutes to read

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Here is a List of essential React JS Interview Questions and Answers for Freshers and mid level of Experienced Professionals. All answers for these React JS questions are explained in a simple and easiest way. These basic, advanced and latest React JS questions will help you to clear your next Job interview.

React JS Interview Questions and Answers

These interview questions are targeted for React developers. You must know the answers of these frequently asked basic and advanced React interview questions to clear an interview. React is becoming more popular and a good choice for developers because of its flexibility and simplicity.

Basic React Interview Questions:

1. What is React?

React is a JavaScript based front-end and open-source library that is used to build UI components or user interfaces. It's developed and maintained by Facebook. React or React.js is used for SPA (Single Page Application) and mobile application development. It's a community of individual developers. For more visit React.

2. What are the advantages and disadvantages of React JS?

React JS is a very popular JavaScript library for building user interfaces. It comes with both advantages and disadvantages as below.
Advantages of React:
  • Easy to Learn and Work - Anyone who has knowledge of JavaScript can learn React in a few days only and it's open-source so any one can contribute to tutorials, docs to help new or existing developers.
  • Component Reusability - React allows you to make modifications to one instance of a component without affecting all other instances of the same component. So you can use the same component at different places as per requirement.
  • SEO Friendly - React provides server-side rendering which mitigates the issue of reading JavaScript-heavy websites for search engines.
  • Performance Improvement via Virtual DOM - Virtual DOM improves the performance of a website as it recreates or updates the modified manipulated element whereas in traditional websites the whole DOM is recreated if the user manipulates any element.
  • One-Way Data Flow - Most of the JS libraries provide data flow in both directions upward and downward but React binds all data to downward meaning - When any changes are made in the child element it does not affect the parent component. It gives more control on large and complex projects.
DisAdvantages of React:
  • Speed of React development - ReactJS is changing so fast that some developers do not feel comfortable to keep up for new React changes.
  • Less Up to date Documentation - Because of the fast pace of React development sometimes it becomes difficult to manage educational documents and tutorials for new changes.
  • JSX - Some developers find JSX syntax extension too difficult and complex to learn and use in the project.
  • Limit for UI Layer only - React JS is only used for building UI layer only, you need to choose some other library and tools for other development work.
For more visit Pros and Cons of React.

3. How will you differentiate React JS and React Native?

React.js is a JavaScript based library to build UI components or user interfaces or UI layer for browser applications. It's just responsible for UI rendering (only View part from MVC Architecture).
ReactNative is a platform to develop cross platform, native mobile applications. It's a framework that comes with many native components and modules to develop high performance mobile applications.

4. What is React Fiber? Differentiate reconciliation and rendering.

React 16 provides a new reconciliation engine known as React fiber which enables incremental rendering of virtual DOM. The Reconciler or reconciliation process just determines which parts of the DOM tree have changed and Renderer updates the rendered app using the inputs from Reconciler. For more visit React Fiber Architecture.

5. Differentiate state and props in React.

state and props both are plain JavaScript objects containing the information which affects the rendering. But the one difference between props and state is that 'props' or properties are passed to components such as you pass parameters to functions whereas 'state' is the part of a component or managed within the component such as local variables inside a function. Other few differences are:
  • props can be changed by parent component but state can not be changed by parent component.
  • props can not be changed inside components but state can be changed inside components.
  • props can be changed inside child components but state can not be changed.
For more you can visit state vs props in React.

6. Explain ref keyword and its usage in React?

7. Explain dirty checks in React.

8. What is prop drilling? How to avoid it?

9. What is Virtual DOM? How does it work in React?

10. Explain React.createClass.

11. Explain the React DOM. How is it different from React?

12. What is the difference between class component and functional component?

13. Explain Event handling in React.

14. What is the use of StrictMode component?

15. What are controlled components in React?

16. Explain Higher Order Components (HOCs). How to create it?

17. What is create-react-app command?

18. What is the use of JSX?

19. What is Redux?

20. What is the use of Redux Thunk?

21. How PureComponent is different from Component?

22. Why do we need keys in React?

23. How would you decide between React JS library and Angular framework?

24. Explain the advantages and disadvantages of shallow rendering components in tests?

25. Explain the use of super() constructor?

26. What is the use of React.createElement?

27. How to update state so that it can re-render the component? Or explain setState() method.

28. Explain ReactJS component lifecycle.

29. What is the use of three dots (...) in React?

30. Explain React Hooks.

31. What are the advantages of Hooks?

32. What is the use of useState() in React?

33. Explain this keyword.

34. Differentiate controller vs uncontrolled component.

35. Explain React context.

36. Explain React Fiber.

37. How to add attributes to components conditionally?

38. What is the difference between using constructor vs getInitialState in React JS?

39. How to update a parent's state in React JS?

40. How will you decide to use class based components vs functional components?

41. What is the most common approach to apply styles to react applications?

42. Explain the difference between useCallback and useMemo.

43. What is the use of componentWillUnmount() method in ReactJS?

https://reactjs.org/docs/design-principles.html

44. How does React JS work?

45. Explain React Design Principles.

Some General Interview Questions for React JS

1. How much will you rate yourself in React JS?

When you attend an interview, Interviewer may ask you to rate yourself in a specific Technology like React JS, So It's depend on your knowledge and work experience in React JS.

2. What challenges did you face while working on React JS?

This question may be specific to your technology and completely depends on your past work experience. So you need to just explain the challenges you faced related to React JS in your Project.

3. What was your role in the last Project related to React JS?

It's based on your role and responsibilities assigned to you and what functionality you implemented using React JS in your project. This question is generally asked in every interview.

4. How much experience do you have in React JS?

Here you can tell about your overall work experience on React JS.

5. Have you done any React JS Certification or Training?

It depends on the candidate whether you have done any React JS training or certification. Certifications or training are not essential but good to have.

Conclusion

We have covered some frequently asked React JS Interview Questions and Answers to help you for your Interview. All these Essential React JS Interview Questions are targeted for mid level of experienced Professionals and freshers.
While attending any React JS Interview if you face any difficulty to answer any question please write to us at info@qfles.com. Our IT Expert team will find the best answer and will update on the portal. In case we find any new React JS questions, we will update the same here.