There are following ReactJS Interview Questions for Freshers software developer in below:
Q1. What is React JS?
React JS is a JavaScript library used for building user interfaces, particularly single-page applications. Developed by Facebook, it allows developers to create reusable UI components.
Q2. What are the key features of React JS?
React JS offers features like virtual DOM for efficient rendering, component-based architecture for reusability, JSX syntax for easy templating, and one-way data binding for predictable state management.
Q3. What is JSX in React?
JSX (JavaScript XML) is a syntax extension used in React for describing the UI components. It allows developers to write HTML-like code within JavaScript, making it easier to visualize and understand the structure of UI components.
Q4. What is a component in React?
In React, a component is a self-contained module that encapsulates a piece of UI. Components can be reusable and can represent any part of a user interface, from simple buttons to complex forms.
Q5. What is a state in React?
State in React is an object that represents the current data of a component. It can be modified over time in response to user actions or other events, triggering UI updates. State management is essential for building interactive and dynamic user interfaces.
Q6. What is props in React?
Props (short for properties) are a way to pass data from parent components to child components in React. They are read-only and are used to customize the behavior and appearance of child components based on the parent’s data.
Q7. What is the difference between state and props in React?
State is managed internally by a component and can be modified over time, while props are passed from parent components and are immutable within the child component. State is used for internal component data, while props are used for inter-component communication.
Q8. What are the lifecycle methods in React?
React components have lifecycle methods that allow developers to hook into different stages of a component’s lifecycle, such as mounting, updating, and unmounting. Examples include componentDidMount, componentDidUpdate, and componentWillUnmount.
Q9. What is the significance of keys in React lists?
Keys are special attributes used by React to identify and track elements in lists. They help React efficiently update the UI by providing a stable identity to each list item, enabling better performance and avoiding unnecessary re-renders.
Q10. What is the purpose of setState() method in React?
setState() is a method used to update the state of a component in React. It triggers a re-render of the component and its children with the updated state, ensuring that the UI reflects the latest data.
Q11. What is the role of virtual DOM in React?
Virtual DOM is a lightweight representation of the actual DOM in memory. React uses it to perform efficient DOM updates by comparing the virtual DOM with the real DOM and applying only the necessary changes, minimizing rendering time and improving performance.
Q12. What are the advantages of using React JS?
React JS offers benefits like improved performance with virtual DOM, component-based architecture for reusability, declarative syntax with JSX, strong community support, and seamless integration with other libraries and frameworks.
Q13. How does React handle events?
In React, event handling is similar to handling events in HTML, but with camelCase syntax. Event handlers are passed as props to components and can be defined inline or as separate methods. React also provides synthetic events for cross-browser compatibility.
Q14. What is the significance of PureComponent in React?
PureComponent is a class component in React that automatically implements shouldComponentUpdate with a shallow prop and state comparison. It helps optimize performance by preventing unnecessary re-renders when the props and state remain unchanged.
Q15. What are controlled and uncontrolled components in React?
Controlled components are components whose data is controlled by React using state or props, while uncontrolled components manage their own state using refs. Controlled components offer better predictability and easier testing, while uncontrolled components can be more flexible in certain scenarios.
Q16. Explain the concept of context in React.
Context is a feature in React that allows data to be passed through the component tree without having to manually pass props at every level. It provides a way to share global data between components without the need for prop drilling.
Q17. How do you handle forms in React?
Forms in React can be handled using controlled components, where form data is managed by React state, or using uncontrolled components with refs. Controlled components offer better control and validation, while uncontrolled components can be simpler for certain use cases.
Q18. What are higher-order components (HOCs) in React?
Higher-order components are functions that take a component as input and return a new component with enhanced functionality. They are used for code reuse, logic abstraction, and cross-cutting concerns like authentication and authorization.
Q19. What are React Hooks?
React Hooks are functions that enable functional components to use state and other React features without writing a class. They allow developers to use stateful logic in functional components, improving code readability and reusability.
Q20. What are the commonly used React Hooks?
Some commonly used React Hooks include useState for managing component state, useEffect for handling side effects in functional components, useContext for accessing context within functional components, and useCallback and useMemo for performance optimization.
Q21. Explain the useReducer Hook in React.
The useReducer Hook is a alternative to useState for managing complex state logic in functional components. It accepts a reducer function and an initial state, and returns the current state and a dispatch function to update the state based on action objects.
Q22. What is server-side rendering (SSR) in React?
Server-side rendering is a technique used to render React components on the server and send the pre-rendered HTML to the client, improving initial page load time and search engine optimization. React provides libraries like Next.js for implementing SSR.
Q23. How do you optimize performance in React applications?
Performance optimization in React can be achieved through techniques like using React.memo for memoization, minimizing re-renders with shouldComponentUpdate or PureComponent, lazy loading components with React.lazy, and code splitting for reducing bundle size.
Q24. What is the purpose of error boundaries in React?
Error boundaries are React components used to catch and handle errors that occur during rendering, event handling, or lifecycle methods of their children components. They help prevent the entire application from crashing due to a single error and provide a fallback UI.
Q25. How do you deploy a React application?
React applications can be deployed to various platforms like Heroku, Netlify, Vercel, or AWS using tools like create-react-app for building optimized production bundles, configuring deployment settings, and deploying to hosting services via Git or CI/CD pipelines.
Summary
These interview questions and answers provide a solid foundation for freshers preparing for React JS interviews, covering key concepts and best practices in React development. Understanding these topics will help candidates demonstrate their proficiency in React and increase their chances of success in interviews. Read more: Online Interview Questions