React Interview Questions

Basic React Questions

1. What is React? React is a JavaScript library for building user interfaces. It is based on a component-based architecture and uses a virtual DOM to efficiently update the UI.

2. What is JSX? JSX is an extension to JavaScript that allows you to write HTML-like syntax in your JavaScript files. It is used to describe the UI components in React applications.

3. What is a component in React? A component is a reusable piece of UI code that encapsulates both its representation and its behavior. Components can be nested within other components to create complex UIs.

4. What is the difference between a functional component and a class component? Functional components are simpler and easier to write, while class components offer more flexibility and state management capabilities.

5. What is the React lifecycle? The React lifecycle refers to the different phases that a component goes through during its lifetime, from mounting to unmounting. Each phase has specific hooks that can be used to perform actions.

6. What is the virtual DOM? The virtual DOM is an in-memory representation of the real DOM. React uses the virtual DOM to efficiently update the UI by comparing the changes between the virtual DOM and the real DOM and applying only the necessary updates.

7. What is controlled and uncontrolled components? Controlled components are components whose input values are managed by React state, while uncontrolled components manage their own input values.

8. What is props? Props are a way to pass data from a parent component to its child components. They are immutable and should not be modified directly.

9. What is state? State is a way to store data that is specific to a component and can be changed over time. State is mutable and can be updated using the setState() method.

Intermediate React Questions

  10. What is a key in React? Keys are unique identifiers that help React efficiently identify and           track individual elements in a list or array.

11. What are higher-order components (HOCs)? HOCs are a way to reuse component logic and create new components that enhance the behavior of existing components.

12. What is context in React? Context is a way to share data across components without having to pass props down through the component tree.

13. What is a React router? A React router is a library that allows you to manage routing and navigation between different pages in a React application.

14. What are React hooks? React hooks are functions that let you “hook into” React state and lifecycle features from function components.

15. What is the difference between useState() and useEffect() hooks? The useState() hook is used to manage local state in a function component, while the useEffect() hook is used to perform side effects, such as data fetching or subscriptions.

Advanced React Questions

   16. What are some performance optimization techniques for React applications? There              are several techniques to optimize React performance, such as using memoization,                  avoiding unnecessary re-renders, and employing PureComponent or React.memo().

17. How can you implement error handling in React applications? React provides error boundaries to handle errors in components and prevent them from crashing the entire application.

18. What are some popular React testing frameworks? Jest and React Testing Library are widely used testing frameworks for React applications.

19. How can you implement accessibility features in React applications? Aria attributes, semantic HTML elements, and focus management are essential aspects of making React applications accessible to users with disabilities.

20. What are some best practices for developing React applications? Following guidelines like using propTypes, writing clean and maintainable code, and employing linting tools are essential practices for developing well-structured React applications.