React Js Online Test

1. In React, how do you conditionally apply styles to components based on component state or props?

By using conditional statements By using the style attribute By using external CSS files By using the class attribute

2. Which CSS-in-JS library is commonly used for styling React components?

Styled Components React Bootstrap Material-UI Redux-Saga

3. What is React's primary purpose in web development?

To manage server-side logic To create user interfaces To store and manage data To handle server requests

4. What is the primary purpose of making HTTP requests in a React application?

To improve the application's performance To retrieve data from external APIs To style components To define component structure

5. Which type of data is typically stored in component state in React?

User input Static configuration Component methods Shared global data

6. What is the recommended approach for structuring tests in a React application?

By organizing tests based on file structure By using a single large test file By writing tests within components By using external test runners

7. Which of the following is a common approach for handling errors in React?

Using console.error to log errors Displaying an error message to the user Redirecting the user to a different page Silently ignoring errors

8. Which lifecycle method should be used to perform cleanup when a component is unmounted?

componentDidMount componentWillUnmount componentWillMount render

9. In React DevTools, what does the "DOM" tab show?

The Document Object Model (HTML structure) The Redux state The application's dependencies The app's source code

10. Which React hook is used for managing state in functional components?

useState renderState componentDidUpdate setState

11. When working with lists in React, which operation is more efficient: adding an item to the beginning or end?

Adding an item to the end of the list Adding an item to the beginning of the list Both operations have the same efficiency It depends on the list size

12. What does the "Props" panel in React DevTools display?

The list of installed npm packages The state of the Redux store The properties and values of a component The app's source code

13. Which command is used to create a new React application using Create React App (CRA)?

create-react-app npm install react react init app npm create-react

14. In React, how do you create a custom Hook for reusing stateful logic across different components?

By defining a function that uses existing Hooks By using the useState Hook directly By extending the Component class By using class components

15. What is the purpose of the package.json file in a React project?

To specify project dependencies To store component code To define global styles To configure Webpack settings

16. Which of the following data formats is commonly used for API responses that contain structured data in React?

JSON XML HTML CSV

17. What is a common method for optimizing images in a React application before deployment?

Using a version control system Compressing and resizing images Minifying JavaScript code Installing more RAM

18. What happens if an error occurs while loading a lazily loaded component in React?

The error is caught and can be handled The application crashes The component is skipped The user is redirected to the homepage

19. What is the purpose of the public directory in a React project?

To store static assets like HTML files To hide sensitive data To define global styles To configure Babel settings

20. What is the primary purpose of React Hooks?

To fetch data from APIs To manage component state To render components To create functional components