Top 50 React Interview Questions and Answers for 2025: From Beginner to Advanced
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Prepare for your React interview with these top 50 questions and answers! Covering beginner to advanced levels, this guide will help you ace any React-related job interview. Perfect for developers aiming to master React concepts.
These questions cover a range of difficulty levels, from beginner to advanced.
1. What is React?
React is a JavaScript library for building user interfaces, maintained by Facebook. It is used for developing single-page applications and mobile apps.
2. What are the features of React?
The main features of React include Virtual DOM, JSX, one-way data binding, component-based architecture, and the ability to manage application state efficiently.
3. What is the Virtual DOM?
The Virtual DOM is a lightweight representation of the real DOM. It updates only the changed elements in the real DOM, improving application performance.
4. What is JSX in React?
JSX stands for JavaScript XML. It is a syntax extension that allows writing HTML-like code within JavaScript files.
5. What are components in React?
Components are independent, reusable pieces of UI in a React application. They can be class components or functional components.
6. What is the difference between class components and functional components?
Class components use ES6 classes and have state and lifecycle methods. Functional components are simpler and can use hooks to manage state and lifecycle.
7. What is state in React?
State is an object that holds data or information about a component. It determines the component's behavior and rendering.
8. What is props in React?
Props, short for properties, are read-only inputs passed to a component from its parent. They are used to pass data between components.
9. What is a React Hook?
Hooks are functions introduced in React 16.8 that allow functional components to use state and lifecycle features without writing class components.
10. What is the use of useState Hook?
The useState Hook allows you to add state to a functional component. It returns an array with the current state and a function to update it.
11. What is the use of useEffect Hook?
The useEffect Hook is used to perform side effects in functional components, such as data fetching, subscriptions, or DOM manipulations.
12. What is the difference between state and props?
State is local to the component and can be modified using setState or useState, while props are read-only and passed from parent to child components.
13. What is Redux?
Redux is a state management library used to manage the state of an application. It is often used with React for building large-scale applications.
14. What is a Pure Component in React?
A Pure Component is a component that performs a shallow comparison of props and state to determine whether to re-render.
15. What is React Router?
React Router is a library for routing in React applications. It allows you to create dynamic and declarative navigation between different components.
16. What is the use of keys in React?
Keys are unique identifiers used by React to identify which items have changed, been added, or removed in a list. They help optimize rendering.
17. What is context in React?
Context is a feature that allows you to share state or data between components without passing props down manually at every level.
18. What is the use of Fragment in React?
Fragment is used to group multiple elements without adding an extra node to the DOM. It is useful for returning multiple elements from a component.
19. What are Higher-Order Components (HOCs)?
HOCs are functions that take a component as an argument and return a new component. They are used to add common functionality to multiple components.
20. What is the use of React.memo?
React.memo is a higher-order component that memoizes a functional component, preventing unnecessary re-renders when props do not change.
21. What is Prop Drilling in React?
Prop Drilling refers to passing props through multiple nested components to reach a deeply nested child component, even if intermediate components do not need the props.
22. How can you prevent Prop Drilling in React?
You can prevent Prop Drilling by using the Context API or state management libraries like Redux to manage and share state globally.
23. What is the purpose of ReactDOM?
ReactDOM is a library that provides methods for rendering React components to the DOM and managing DOM elements in web applications.
24. What is the difference between controlled and uncontrolled components?
Controlled components are those where form data is handled by the component's state, while uncontrolled components rely on the DOM to manage form data.
25. What is the use of refs in React?
Refs provide a way to directly access and interact with a DOM element or React element created in the render method.
26. What is the StrictMode in React?
StrictMode is a development tool in React that helps identify potential problems in an application by activating additional checks and warnings.
27. What is lazy loading in React?
Lazy loading is a technique used to load components or resources only when they are needed, improving the performance of the application.
28. How is code splitting achieved in React?
Code splitting can be achieved using React's lazy() function and dynamic imports with Webpack to load components asynchronously.
29. What is the difference between useMemo and useCallback?
useMemo is used to memoize a computed value, while useCallback is used to memoize a callback function to avoid unnecessary re-creation.
30. What is reconciliation in React?
Reconciliation is the process through which React updates the DOM by comparing the Virtual DOM with the previous Virtual DOM and applying changes efficiently.
31. What are React Portals?
React Portals allow you to render a child component outside of its parent component's DOM hierarchy, typically used for modals or tooltips.
32. What is the use of error boundaries in React?
Error boundaries are React components that catch JavaScript errors in their child component tree, log the errors, and display fallback UI.
33. What is the purpose of the key attribute in React lists?
The key attribute helps React identify which items in a list have changed, been added, or removed, optimizing the rendering process.
34. Can you explain React Fiber?
React Fiber is the re-implementation of React's reconciliation algorithm, enabling incremental rendering and prioritizing updates for better performance.
35. What are synthetic events in React?
Synthetic events are React's cross-browser wrapper around native events. They ensure consistent behavior across different browsers.
36. How does React handle forms?
React handles forms using controlled or uncontrolled components. Controlled components manage form data using state, while uncontrolled components rely on refs.
37. What is the use of the defaultValue property in forms?
The defaultValue property is used to set the initial value of an uncontrolled input field in React forms.
38. What are React fragments, and why are they used?
React fragments allow you to group multiple elements without adding extra nodes to the DOM, which helps keep the DOM clean.
39. What is the use of forwardRef in React?
forwardRef is used to pass refs to child components, allowing the parent to directly access a child component's DOM element.
40. What is React's StrictMode used for?
StrictMode helps identify potential issues in the application by activating additional warnings and checks during development.
41. How can you optimize a React application?
Optimizations include using React.memo, useCallback, useMemo, code splitting, lazy loading, and avoiding unnecessary re-renders.
42. What is hydration in React?
Hydration is the process of attaching event listeners and React functionality to server-rendered HTML to make it interactive.
43. How do you handle conditional rendering in React?
Conditional rendering can be handled using if-else statements, ternary operators, or logical && operators within JSX.
44. What is the difference between React and React Native?
React is used for building web applications, while React Native is used for building mobile applications using React concepts.
45. What is the use of the useReducer Hook?
The useReducer Hook is an alternative to useState, used to manage complex state logic in functional components.
46. What is the purpose of the useRef Hook?
useRef is used to create a mutable ref object that persists across renders, commonly used to access DOM elements directly.
47. How do you pass data between sibling components in React?
Data can be passed between sibling components by lifting state up to their common parent and passing it as props to each sibling.
48. What are custom Hooks in React?
Custom Hooks are user-defined functions that allow you to extract reusable stateful logic from components.
49. What is the purpose of React's render method?
The render method is used to describe what the UI should look like by returning React elements, which are then rendered to the DOM.
50. How do you update the state of a component in React?
State in class components is updated using the setState method, and in functional components, it is updated using the updater function returned by useState.