React.js interview questions

1. Can you explain the virtual DOM in React?
2. How does React handle server-side rendering?
3. What is the difference between state and props in React?
4. How do you implement a controlled component in React?
5. Can you explain the lifecycle methods of a React component?
6. How do you handle forms and form validation in React?
7. How do you optimize the performance of a React application?
8. Can you explain the concept of Higher-Order Components (HOC) in React?
9. How do you handle events in React?
10. Can you explain the concept of "lifting state up" in React?
11. How do you implement debugging and troubleshooting in a React application?
12. Can you explain the concept of React Router and how it works?
13. How do you handle different environments (e.g. development, staging, production) in a React application?
14. How do you test a React application?
15. Can you explain the concept of "reconciliation" in React and how it works?
16. How do you implement internationalization (i18n) in a React application?
17. How do you handle errors and exceptions in a React application?
18. Can you explain the concept of hooks in React and how they differ from class components?
19. How do you implement accessibility in a React application?
20. How do you integrate a React application with a back-end API?

These are some common questions that may be asked in an interview for a React.js developer position. The level of detail and the specific areas of focus may vary depending on the interviewer and the company.