React.js Interview Questions and Answers for internship

0
React.js Internship Interview Questions and Answers

  1. What is React.js?

    • Answer: React.js is a JavaScript library for building user interfaces (UIs), specifically single-page applications. It's maintained by Facebook and a community of individual developers and companies. React's core strength lies in its component-based architecture and virtual DOM, which enable efficient updates and rendering.

  2. Explain JSX.

    • Answer: JSX (JavaScript XML) is a syntax extension to JavaScript. It allows you to write HTML-like code within your JavaScript code. This makes it easier to describe the structure of the UI and improves readability. JSX is not strictly necessary for React, but it's widely used and preferred for its ease of use.

  3. What is a component in React?

    • Answer: In React, a component is an independent, reusable piece of UI. Components can be either functional components (simple JavaScript functions) or class components (ES6 classes extending React.Component). They encapsulate logic and rendering, making code more organized and maintainable.

  4. What is the difference between functional and class components?

    • Answer: Functional components are simpler and are just JavaScript functions that return JSX. They are preferred for simpler components. Class components are ES6 classes that extend React.Component, providing lifecycle methods (like `componentDidMount`, `componentDidUpdate`, `componentWillUnmount`) for managing state and side effects. Functional components can now also use hooks to manage state and side effects, making them a more common choice even for complex components.

  5. Explain the virtual DOM.

    • Answer: The virtual DOM is a lightweight in-memory representation of the actual DOM. When changes occur in the React application, React first updates the virtual DOM. Then, React compares the updated virtual DOM with the previous version to determine the minimal changes needed in the actual DOM. This efficient diffing process minimizes direct manipulations of the real DOM, resulting in significantly better performance.

  6. What are props in React?

    • Answer: Props (short for properties) are a way to pass data from a parent component to a child component. Props are read-only; child components cannot modify the props received from their parents. This unidirectional data flow is crucial for React's predictable behavior.

  7. What is state in React?

    • Answer: State is an internal data structure of a component. Changes to the state trigger re-rendering of the component and its children. State is mutable, unlike props.

  8. How do you lift state up in React?

    • Answer: Lifting state up involves moving the state from a child component to a shared parent component that both child components can access. This is done to manage state that is shared between multiple child components and maintain data consistency.

  9. Explain React hooks (useState, useEffect).

    • Answer: React hooks are functions that let you "hook into" React state and lifecycle features from within functional components. `useState` lets you manage state in functional components. `useEffect` lets you perform side effects, like data fetching or subscriptions, in functional components. They simplify code and make functional components more powerful.

  10. What are lifecycle methods in class components?

    • Answer: Lifecycle methods are special methods in class components that are called at different stages of a component's existence. Examples include `componentDidMount` (called after the component is rendered), `componentDidUpdate` (called after an update), and `componentWillUnmount` (called before the component is unmounted from the DOM).

  11. Explain event handling in React.

    • Answer: Event handling in React is done using JSX attributes that correspond to DOM events (e.g., `onClick`, `onChange`, `onSubmit`). Event handlers are JavaScript functions that are executed when the corresponding event occurs. The `event` object is passed as an argument to the handler.

  12. What is key prop in React?

    • Answer: The `key` prop is a special prop used with array elements when rendering lists in React. It helps React identify which items have changed, been added, or removed, resulting in efficient updates and preventing unnecessary re-renders. It should be a unique identifier for each item in the list.

  13. What are controlled and uncontrolled components?

    • Answer: Controlled components have their values managed by the React component's state. Uncontrolled components rely on the DOM's internal state. Controlled components are generally preferred for better control and predictability.

  14. Explain conditional rendering in React.

    • Answer: Conditional rendering allows you to render different UI elements based on certain conditions. This can be achieved using JavaScript `if` statements, ternary operators, or logical AND/OR operators directly within JSX.

  15. How to handle forms in React?

    • Answer: Forms in React are typically handled as controlled components. The form's values are stored in the component's state, and changes to the form inputs update the state. Event handlers manage the submission of the form, typically using `onSubmit`.

  16. What are higher-order components (HOCs)?

    • Answer: Higher-order components are functions that take a component as an argument and return a new enhanced component. They are used for code reuse, adding functionality to existing components (like logging, data fetching, or authentication) without modifying their original code.

  17. What are render props?

    • Answer: Render props are a technique for sharing code between React components using a prop whose value is a function. This function is called by the parent component and receives data from the child component, allowing it to render custom UI based on that data. They are an alternative to HOCs for code reuse and sharing logic.

  18. What are React context API?

    • Answer: The React Context API provides a way to pass data through the component tree without having to pass props down manually at every level. This is useful for sharing data that many components need to access.

  19. Explain Fragment in React.

    • Answer: Fragments are a way to group multiple elements together without adding extra nodes to the DOM. They are represented by `` or the shorthand `<>`.

  20. What are refs in React?

    • Answer: Refs provide a way to directly access DOM elements or component instances. They are used for scenarios where you need to manipulate the DOM directly or access component methods.

  21. What is the difference between `setState` and `forceUpdate`?

    • Answer: `setState` is the standard way to update a component's state. It triggers a re-render efficiently. `forceUpdate` forces a re-render without comparing the previous and new states. It should generally be avoided because it can lead to performance issues.

  22. How do you handle errors in React?

    • Answer: Error handling in React is done using error boundaries. Error boundaries are components that catch errors in their child component tree and display a fallback UI.

  23. Explain React Router.

    • Answer: React Router is a popular library for implementing navigation and routing in React applications. It enables creating single-page applications with multiple views.

  24. What are some common React patterns?

    • Answer: Some common React patterns include composition, higher-order components (HOCs), render props, context API, and hooks.

  25. How do you optimize React applications for performance?

    • Answer: Performance optimization techniques for React include using `React.memo`, `useMemo`, `useCallback`, code splitting, lazy loading, and optimizing image sizes.

  26. What are some tools for debugging React applications?

    • Answer: Common debugging tools include the React Developer Tools browser extension and the Chrome DevTools.

  27. What is Redux? Why is it used with React?

    • Answer: Redux is a predictable state container for JavaScript apps. It's often used with React to manage complex application state, especially in large-scale projects where state management becomes challenging. It provides a centralized store for application state and makes state updates predictable and easy to track.

  28. What is the difference between React and Angular?

    • Answer: React is a JavaScript library for building UIs, while Angular is a complete framework for building full-fledged applications. Angular has a steeper learning curve but offers more built-in features and structure.

  29. What is a good way to structure a React project?

    • Answer: A good React project structure typically involves organizing components into folders based on their functionality and using a consistent naming convention for files and components. Often a feature-based or domain-driven design approach is used.

  30. Explain how you would approach building a specific React component (e.g., a to-do list item).

    • Answer: I would start by defining the component's props (e.g., `text`, `completed`), state (e.g., `isCompleted`), and render JSX based on the props and state. I would use event handlers to handle user interactions (e.g., toggling completion). I'd ensure clear separation of concerns and potentially use hooks for state management and side effects if appropriate.

  31. Describe your experience with testing in React.

    • Answer: [Answer should describe experience with testing frameworks like Jest and React Testing Library. It should mention different types of tests (unit, integration, snapshot) and methodologies for writing effective tests.]

  32. How familiar are you with TypeScript and its use with React?

    • Answer: [Answer should describe level of familiarity with TypeScript, including its benefits for type safety and maintainability in React projects. Mention experience with type annotations and using TypeScript with React components.]

  33. What are some best practices for writing clean and maintainable React code?

    • Answer: Best practices include using a consistent coding style, following component design principles (single responsibility, separation of concerns), using meaningful component names, writing clear and concise code, and using linting tools.

  34. How do you handle asynchronous operations in React?

    • Answer: Asynchronous operations are commonly handled using promises, async/await, and the `useEffect` hook (with cleanup functions for managing side effects).

  35. Explain your understanding of server-side rendering (SSR) in React.

    • Answer: SSR renders the React application on the server, sending the fully rendered HTML to the client. This improves SEO, performance, and initial load times.

  36. What are some common performance bottlenecks in React applications and how would you address them?

    • Answer: Common bottlenecks include excessive re-renders, inefficient state updates, and large component trees. Addressing them requires techniques such as using `React.memo`, `useCallback`, `useMemo`, optimizing state updates, and code splitting.

  37. How familiar are you with different state management libraries besides Redux? (e.g., Zustand, Jotai, Recoil)

    • Answer: [Answer should describe familiarity with alternative state management libraries, highlighting their strengths and weaknesses compared to Redux and when they might be preferred.]

  38. Describe your experience working with RESTful APIs in a React application.

    • Answer: [Answer should describe experience making HTTP requests using `fetch` or Axios, handling responses, and potentially using libraries like SWR or React Query for data fetching and caching.]

  39. How would you approach implementing accessibility features in your React components?

    • Answer: I would focus on proper ARIA attributes, semantic HTML, keyboard navigation, and color contrast ratios to ensure accessibility.

  40. Describe a challenging React project you've worked on and how you overcame the challenges.

    • Answer: [Answer should describe a specific project, highlighting challenges encountered and the solutions implemented. This demonstrates problem-solving skills and technical abilities.]

  41. What are your preferred methods for learning new technologies?

    • Answer: [Answer should demonstrate a proactive approach to learning, such as reading documentation, online courses, experimenting with code, and collaborating with others.]

  42. Tell me about a time you had to debug a complex issue in a React application.

    • Answer: [Answer should illustrate debugging skills, using tools effectively, and systematically identifying and solving the problem.]

  43. Why are you interested in this React.js internship?

    • Answer: [Answer should clearly express genuine interest in the internship, the company, and the opportunity to learn and grow.]

  44. What are your salary expectations?

    • Answer: [Answer should be a realistic range based on research and experience.]

Thank you for reading our blog post on 'React.js Interview Questions and Answers for internship'.We hope you found it informative and useful.Stay tuned for more insightful content!