Questions Asked in React.js Interview.

Hey there, fellow code warriors! I'm Prajesh, your friendly neighborhood dev, here to drop some ‘free gyaan’—because why pay when you can scroll? 😆 Now, congrats on finding this post! If you’re here, you’re probably doing the classic interview panic search, just like I do five minutes before the call. (Hey, it works sometimes! 😂) If not, maybe you’re just overly ambitious. Either way, good on ya!

Now, you’re probably wondering: What makes my React interview questions so special? Well… plot twist—they’re not. You’ll see these questions in other blogs too. So why stick around? Because these are the exact questions that popped up in my interviews, and trust me, every React dev should have these locked and loaded. Plus, I’m spilling the tea on what interviewers are actually looking for when they ask these tricky questions—plus some sneaky tips to nail ‘em like a pro.

If you’re still reading, you clearly trust my wisdom (wise choice). Stick around for some insights below, or if you're just here for the questions, scroll straight on down. May the JavaScript gods be with you!

Note: I have given a lot of interviews 😂.

Free Gyaan

If you’re heading into an interview for a frontend or fullstack role, keep these in mind—it’s like packing snacks for a long trip; you’ll thank me later:

1. JavaScript is king: Expect a parade of JavaScript questions, from the easy-breezy to the downright evil. Most new devs don’t prepare well enough, and trust me, interviewers know this. So, brush up on your basics, and don’t skip the tricky stuff—closures, promises, async/await, and maybe that one quirky thing called this.

2. Get ready to code: They’ll likely throw a JavaScript coding problem your way or ask you to whip up a small React feature. Don’t just build it—make it sparkle! Oh, and once you think you’re done, brace yourself for the dreaded “Can you optimize this?” or “What if we tweak it a little?” (Translation: We just want to watch you squirm.)

3. API integration is your BFF: Learn to wield Axios like a pro. Many interviewers love tasks like “fetch this data and display it” or “modify this API response.” If you can make API calls while looking calm, they might even clap. (Spoiler: They won’t, but hey, you’ll still ace it.)

4. Don’t ghost HTML and CSS: These are the unsung heroes of frontend, and ignoring them could cost you. Most interviewers will throw basic HTML/CSS questions your way, and some will even toss in a small task like creating a responsive box or styling a layout. Pro tip: It’s like solving a puzzle, but the pieces are invisible and on fire.

5. Know React’s extended family: React Native and Next.js might pop up in conversation. You don’t need to be a wizard, but showing that you’ve heard of them and understand the basics will score you bonus points. It’s like knowing your distant cousins—you don’t hang out much, but you’re polite when they visit.

Short version? Study up, stay calm, and remember—they want you to succeed… probably. 😉 Good luck, and may your code always run on the first try (but let’s be real, it won’t).

ReactJS Interview Questions Fired On Me:

Now, now, I know what you’re thinking: 'Why on earth aren’t the answers here?!' But trust me, it’s for your own good. Searching for answers yourself is like going on a treasure hunt—you’ll not only learn better but also understand and remember more effectively. Plus, it’s always smarter to learn from multiple sources rather than just one. Think of it as assembling a super-team of knowledge, instead of relying on just one hero. Diversity is key, even in learning! So, roll up your sleeves, open those tabs, and get cracking.

1. What is React?
Here, the interviewer is likely expecting you to say React is a library, not a framework.
2. What is JSX, and how is it different from HTML?
3. What is the DOM tree, and how does React interact with it?
4. What are props in React, and how are they passed to components?
The interviewer might throw a curveball here, asking about destructuring, spread/rest operators, so be ready to flex those JavaScript muscles.
5. What are keys in React, and why are they important?
6. What is the virtual DOM, and how does it work?
7. What are lifecycle methods in React, and how are they used?
Lifecycle methods in class components and functional components are like different species... don’t mix them up!
8. What is a Higher-Order Component (HOC) in React?
9. What are controlled and uncontrolled components in React?
10. What are React hooks, and how do they enhance React functionality?
11. What is useState, and how does it work?
12. What is useEffect, and when should it be used?
13. What is the useContext hook, and how is it used in React?
14. What are useRef, useMemo, and useCallback, and how are they used?
Focus on useRef, it’s for when you want to manipulate the real DOM
15. What is lazy loading, and how is it implemented in React?
16. How can you optimize a React application for performance?
17. What is Strict Mode in React, and what is its purpose?
18. How can we prevent unnecessary re-renders in React?
19. What is props drilling, and how can it be minimized?
20. Can we create custom hooks in React, and how are they useful?
Yes, you can! Custom hooks are like your personal React assistant. They organize code and save you from repetitive tasks.
21. How does useReducer work in React, and how is it different from Redux?
22. What is reconciliation in React?
23. How many times does a React application render during startup?
24. What are pure components in React, and when should they be used
25. What is the debugger keyword in JavaScript, and how does it work in React?
Jest, React Testing Library, and Enzyme are your go-to squad for testing.
26. What are the differences between reduce, filter, forEach, and map in JavaScript?
27. What is optional chaining, and how does it work in JavaScript?
28. What are the differences between JSX and TSX?
29. What is Redux, and how is it used in React applications?
30. What is the difference between server-side and client-side components?
31. How can you make a React application re-render infinitely, and why would you want to avoid this?
32. How would you handle complex form validation in React?
33. What are some popular testing tools for React and UI testing?
34. What is the latest version of React, and what new features does it include?

Thank you so much for taking the time to read ❤️!

Comments

[vigneshiyergithub]

Good set of initial entry questions, Prajesh! This list is perfect for prepping the fundamentals. But don’t forget—interviews, especially those for mid to senior-level positions, often dive into more nuanced, real-world React challenges. Here’s what I’d recommend you be ready for:

Advanced React Topics You Should Master:

• Deep Dive into useEffect: This hook is more than just fetching data or updating the DOM. Interviewers love to explore its gotchas—like dependency array pitfalls, potential race conditions, and cleanup functions. Be ready to explain when useEffect becomes a problem (e.g., memory leaks or infinite loops) and strategies to optimize or replace it when necessary.

• Routing Best Practices: Beyond basic route declarations, know how to implement Role-Based Access Control (RBAC) in your routing logic. This can involve securing routes based on user roles, dynamic route rendering, and route guards for more complex applications. Be prepared to discuss libraries like React Router and best practices for scalable, secure routing.

• State Management Breakdown:

  • Local vs. Global State: When to lift state up, use useContext, or transition to more robust solutions like Redux or Zustand.
  • Server State Management: Handling data from APIs efficiently using tools like React Query and managing state synchronization between the server and client.

• Applying SOLID Principles with React: Show how you incorporate SOLID design principles into React development. Interviewers might ask how you ensure single responsibility within components, or how you use dependency inversion with hooks for better testability and modularity.

• Complex Form Management: Think beyond basic useState hooks for form handling. Be prepared to discuss libraries like Formik or React Hook Form for scalable solutions. Also, touch on handling complex validations, dynamic form fields, and keeping forms performant with minimal re-renders.

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Nailing down these advanced topics can make the difference between getting by and standing out. Master them, and you won’t just pass interviews—you’ll own them. Good luck, and remember: no interview is too tough if you’re ready to flex those coding muscles!

[Prajesh Gawhale]

Thank you for the thoughtful feedback and great insights! 😊 I completely agree—mid to senior-level interviews often dive deeper into topics like useEffect quirks, advanced routing, state management, and SOLID principles. Your suggestions on mastering these areas are spot on and a great reminder to always grow beyond the basics. I’ll definitely keep these in mind for future updates. Thanks for sharing your expertise!