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🌟 Latest React and Js interview Questions 2025

React , JavaScript and TypeScript Interview Questions

  1. Microtasks vs MacroTasks

    • What is the difference between Microtasks and Macrotasks in JavaScript’s event loop?
    • Can you give an example of code that executes as a Microtask vs a Macrotask?

  2. npm vs npx

    • What is the difference between npm and npx?
    • When would you use npx instead of npm?

  3. Class Components vs Function Components

    • How do class components differ from function components in React?
    • Which one is preferred in modern React and why?

  4. DOM vs Virtual DOM

    • What is the difference between the DOM and Virtual DOM in React?
    • How does React’s Virtual DOM improve performance?

  5. useMemo vs React.memo

    • What’s the difference between useMemo and React.memo?
    • Give a use case where you would use useMemo instead of React.memo.

  6. Higher-Order Components (HOCs)

    • What is a Higher-Order Component in React?
    • Can you explain a real-world use case for HOCs?

  7. Managing State in React

    • What are the different ways to manage state in a React app?
    • When would you choose Context API vs Redux for state management?

  8. useLayoutEffect

    • What is useLayoutEffect and how is it different from useEffect?
    • When should you use useLayoutEffect?

  9. useRef vs createRef

    • What’s the difference between useRef (hook) and createRef (class-based)?
    • Can refs cause memory leaks?

  10. React Hook Form

    • What is React Hook Form and why is it used?
    • How does it compare with Formik?

  11. Managing Data & Sending to API

    • How do you manage form data in React and send it to an API?
    • How would you handle API errors when submitting a form?

  12. 10 Text Boxes Form

    • If you have 10 text inputs in a form, how would you manage their state?
    • Would you use a single state object or multiple useState hooks? Why?

  13. Redux

    • What are the core principles of Redux?
    • Can you explain the flow of data in Redux with an example?

  14. Axios

    • Why do we use Axios instead of Fetch API?
    • How do you intercept requests and responses in Axios?

  15. useFormContext Hook

    • What is the purpose of useFormContext in React Hook Form?
    • How does it help with deeply nested forms?

  16. Routing in React

    • How does routing work in React using React Router?
    • Difference between BrowserRouter and MemoryRouter?

  17. Authentication & Authorization in React

    • How do you implement authentication and authorization in React?
    • How do you protect routes based on user roles?

  18. Callback Queue & Callback Functions

    • What is the callback queue in JavaScript’s event loop?
    • How do callback functions work in asynchronous code?

  19. Closures

    • What is a closure in JavaScript?
    • Can you give a practical example of a closure in React?

  20. any vs unknown (TypeScript)

    • What’s the difference between any and unknown in TypeScript?
    • Which one is safer and why?

  21. Tree Shaking in React

    • What is tree shaking and how does it help in React apps?
    • How can you ensure your code benefits from tree shaking?

  22. JS Memory Management & Garbage Collection

    • How does JavaScript manage memory?
    • What are memory leaks and how can they be avoided?

  23. Compound Component Pattern

    • What is the compound component pattern in React?
    • Can you give an example (like a Tab system)?

  24. WeakMap vs WeakSet

    • Difference between WeakMap and WeakSet?
    • Why are they useful for memory management?

  25. Shallow Copy vs Deep Copy

    • Difference between shallow copy and deep copy?
    • How would you create a deep copy in JavaScript?

  26. Promises & Error Handling

    • How do you handle errors in Promises?
    • Difference between .catch and try...catch with async/await?

  27. Map, Filter, Reduce

    • How do map, filter, and reduce differ?
    • Write an example of each.

  28. Debounce vs Throttle

    • What is the difference between debouncing and throttling?
    • Give a real-world scenario for each.

  29. useTransition (React 18)

    • What is useTransition in React?
    • How does it improve UI responsiveness?

  30. Phases in Functional Components

    • What are the different phases of a functional component lifecycle?
    • How do hooks replace lifecycle methods?

  31. Mounting & Unmounting

    • What happens during mounting and unmounting in React?
    • How can you perform cleanup on unmount?

  32. Methods in Class Components

    • What are lifecycle methods in class components?
    • How do they compare with hooks in functional components?

  33. BrowserRouter vs MemoryRouter

    • Difference between BrowserRouter and MemoryRouter?
    • When would you use MemoryRouter?

  34. Hydration in React

    • What is hydration in React?
    • Why is it important for SSR (Server-Side Rendering)?

  35. startTransition (React 18)

    • What is startTransition and how is it different from useTransition?
    • Can you give an example?

  36. Custom Hooks

    • What are custom hooks in React?
    • How do they improve reusability?

  37. Synthetic Events in React

    • What are synthetic events in React?
    • How are they different from native DOM events?

  38. Memory Leaks

    • What causes memory leaks in React or JavaScript?
    • How can you prevent them?

  39. Lazy Loading & Performance Optimization

    • How does lazy loading work in React?
    • What other techniques can optimize React performance?

  40. Calling Parent Function from Child

    • Can a child component call a parent’s function in React?
    • How would you implement it?

  41. Memory Leak in React/JS

    • What are common causes of memory leaks in React/JavaScript?
    • How do you detect and fix them? 
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