1. What is ReactJS?

ReactJS is an open-source JavaScript library used for building user interfaces or UI components. It was developed by Facebook and is used widely to develop single-page applications (SPAs).

2. What is JSX?

JSX is a syntax extension for JavaScript that allows developers to write HTML-like code in their JavaScript code. It makes it easier to create and manipulate the virtual DOM tree in React.

3. What is a Virtual DOM?

A Virtual DOM is a lightweight representation of the actual DOM that React uses to keep track of changes and efficiently update the UI. When there is a change in the state of a component, React updates the Virtual DOM and then compares it with the actual DOM to determine what needs to be changed.

4. What are the advantages of using ReactJS?

Some of the advantages of using ReactJS include its ability to handle complex UIs, improved performance through the use of the Virtual DOM, and its modular approach to building UI components.

5. What are the differences between state and props in React?

The state is used to store and manage data within a component, while props are used to pass data from one component to another. The state is managed within the component, while props are passed down from the parent component to its child components.

6. What is the significance of keys in React?

Keys are used to identifying the individual components within a list or a set of elements. They help React to efficiently update the DOM when there are changes in the state of the components.

7. What is the role of the render method in React?

The render method is responsible for rendering the UI of a component. It is called every time there is a change in the state of the component, and it returns the updated UI.

8. What is the significance of the componentDidMount() method in React?

The componentDidMount() method is called after a component is mounted and is ready to be rendered. It is used to load data from external sources or perform any necessary setup operations.

9. What is the significance of the componentWillUnmount() method in React?

The componentWillUnmount() method is called before a component is unmounted and removed from the DOM. It is used to perform any necessary cleanup operations or remove any event listeners.

10. What is the difference between a controlled and an uncontrolled component in React?

In a controlled component, the value of the component is controlled by the state of the parent component, while in an uncontrolled component, the value is controlled by the DOM itself. Controlled components are recommended as they provide a better way to manage the state of a component.

11. What is the significance of the shouldComponentUpdate() method in React?

The shouldComponentUpdate() method is used to optimize the performance of a React application by preventing unnecessary re-renders of components. It determines whether a component should be re-rendered when there is a change in its state or props.

12. What is the significance of the setState() method in React?

The setState() method is used to update the state of a component. When the state of a component changes, React updates the Virtual DOM and re-renders the component to reflect the changes.

13. What is the role of React Router?

React Router is a library used to handle routing in a React application. It allows developers to create multiple pages or views in a single-page application (SPA) and manage the application's URL.

14. What is the significance of the useRef() hook in React?

The useRef() hook is used to create a mutable object that persists between renders of a component. It can be used to store references to DOM elements, create a counter, or store any other data that needs to persist between renders.

15. What is the significance of the useContext() hook in React?

The useContext() hook is used to access a context object that is passed down from a parent component. It allows components to access shared data without having to pass props down through every level of the component hierarchy.

16. What is the significance of the useEffect() hook in React?

The useEffect() hook is used to perform side effects in a React component. It is called after every render and can be used to update the DOM, make network requests, or update the state of the component.

17. What is Redux?

Redux is a state management library for JavaScript applications. It provides a way to manage the state of an application in a predictable and centralized way.

18. What is the significance of the connect() function in Redux?

The connect() function is used to connect a component to the Redux store. It allows the component to access the state of the store and dispatch actions to update the store.

19. What is a reducer in Redux?

A reducer is a pure function that takes the current state of the application and an action and returns a new state. It is used to update the state of the application in response to actions dispatched by the component.

20. What is a middleware in Redux?

A middleware is a function that intercepts actions before they reach the reducer. It can be used to modify the action, dispatch additional actions, or perform side effects such as making network requests.

21. What is React Native?

React Native is a framework used to build mobile applications for iOS, Android, and other platforms using React. It allows developers to write mobile applications using the same code as a web application.

22. What is the significance of the StyleSheet API in React Native?

The StyleSheet API is used to create styles for components in a React Native application. It is similar to CSS but is optimized for mobile devices.

23. What is the significance of the Flexbox layout in React Native?

The Flexbox layout is a way of laying out components in a React Native application. It allows developers to create responsive and dynamic layouts that can adapt to different screen sizes and orientations.

24. What is the significance of the Touchable components in React Native?

The Touchable components are a set of components in React Native that allow developers to create buttons, links, and other interactive elements in a mobile application. They provide a way to handle touch events and respond to user input.

25. What is the significance of the AsyncStorage API in React Native?

The AsyncStorage API is used to store data persistently in a React Native application. It allows developers to store data such as user preferences or app settings on the device.

26. What is the difference between React and React Native?

React is a library used to build user interfaces for web applications, while React Native is a framework used to build mobile applications for iOS, Android, and other platforms.

27. What is the significance of the fetch() function in React Native?

The fetch() function is used to make network requests in a React Native application. It is similar to the XMLHttpRequest object in JavaScript and can be used to make GET, POST, and other types of requests.

28. What is the significance of the FlatList component in React Native?

The FlatList component is used to display a large list of data in a React Native application. It is optimized for performance and can handle large datasets without impacting the performance of the application.

29. What is the significance of the SafeAreaView component in React Native?

The SafeAreaView component is used to ensure that the content of a React Native application is displayed within the safe area of a device's screen. It ensures that the content is not hidden behind the device's status bar or home indicator.

30. What is the significance of the Animated API in React Native?

The Animated API is used to create animated components in a React Native application. It allows developers to create animations that respond to user input or changes in the state of the application.

31. What is the significance of the Image component in React Native?

The Image component is used to display images in a React Native application. It supports various image formats, including JPG, PNG, and GIF.

32. What is the significance of the TextInput component in React Native?

The TextInput component is used to capture user input in a React Native application. It provides a way to handle user input and allows users to enter text or other data into a mobile application.

33. What is the significance of the StatusBar component in React Native?

The StatusBar component is used to display the status bar in a React Native application. It allows developers to customize the appearance of the status bar and respond to changes in the status bar, such as changes in network connectivity.

34. What is the significance of the WebView component in React Native?

The WebView component is used to display web content within a React Native application. It allows developers to display web pages or other web-based content within a mobile application.

35. What is the significance of the Navigation component in React Native?

The Navigation component is used to manage navigation between screens in a React Native application. It allows developers to create navigation stacks, tabs, and other navigation patterns within a mobile application.

36. What is the significance of the CameraRoll API in React Native?

The CameraRoll API is used to access the camera roll on a device in a React Native application. It allows developers to access and display images and videos stored on the device.

37. What is the significance of the Permissions API in React Native?

The Permissions API is used to request permission from the user to access certain features on a device, such as a camera, microphone, or location. It allows developers to provide a better user experience by requesting permissions when needed.

38. What is the significance of the Dimensions API in React Native?

The Dimensions API is used to get the dimensions of the device screen in a React Native application. It allows developers to create responsive layouts that adapt to different screen sizes.

39. What is the significance of the Platform API in React Native?

The Platform API is used to determine the platform on which a React Native application is running. It allows developers to write platform-specific code and customize the behavior of the application for different platforms.

40. What is the significance of the Linking API in React Native?

The Linking API is used to handle deep linking in a React Native application. It allows developers to handle links to their applications from other apps or the web and provides a way to navigate to specific screens within the application.

41. What is the significance of the Redux library in React?

Redux is a state management library used in React applications. It provides a way to manage the state of the application and allows for predictable, centralized data flow.

42. What is a Higher-Order Component (HOC) in React?

A Higher-Order Component is a function that takes a component as an argument and returns a new component with additional functionality. It is used to enhance the functionality of a component without modifying the original component.

43. What is the significance of the Context API in React?

The Context API is used to share data between components in a React application. It provides a way to pass data down the component tree without using props.

44. What is the significance of the useCallback hook in React?

The useCallback hook is used to memoize a function in a React component. It allows for better performance by avoiding unnecessary re-renders when a component's state or props change.

45. What is the significance of the useEffect hook in React?

The useEffect hook is used to perform side effects in a React component. It allows for handling state changes, fetching data, and subscribing to events.

46. What is the significance of the useMemo hook in React?

The useMemo hook is used to memoize a value in a React component. It allows for better performance by avoiding unnecessary calculations when a component's state or props change.

47. What is the significance of the useRef hook in React?

The useRef hook is used to create a mutable reference in a React component. It allows for accessing and modifying the properties of a component without triggering a re-render.

48. What is the significance of the useState hook in React?

The useState hook is used to manage the state in a React component. It allows for storing and updating state data without modifying the component directly.

49. What is the significance of the useReducer hook in React?

The useReducer hook is used to manage the state in a React component using a reducer function. It allows for more complex state management and allows for predictable state changes.

50. What is the significance of the useCallback hook in React?

The useCallback hook is used to memoize a function in a React component. It allows for better performance by avoiding unnecessary re-renders when a component's state or props change.

51. What is the significance of the useHistory hook in React Router?

The useHistory hook is used to access the browser history in a React Router application. It allows for programmatic navigation between pages in the application.

52. What is the significance of the useParams hook in React Router?

The useParams hook is used to access the parameters in a URL in a React Router application. It allows for dynamic routing based on the URL parameters.

53. What is the significance of the useLocation hook in React Router?

The useLocation hook is used to access the current URL location in a React Router application. It allows for accessing information about the current URL path, search parameters, and hash.

54. What is the significance of the withRouter higher-order component in React Router?

The withRouter higher-order component is used to provide access to the router history, and location, and match props to a component that is not directly rendered by a Route component in a React Router application.

55. What is the significance of the Switch component in React Router?

The Switch component is used to render only the first matching Route component in a React Router application. It allows for specifying a fallback route if no other routes match the current URL path.

56. What is the significance of the Redirect component in React Router?

The Redirect component is used to redirect a user to a different URL path in a React Router application. It allows for programmatic navigation between pages.

57. What is the significance of the Route component in React Router?

The Route component is used to define a route in a React Router application. It allows for matching the URL path to a specific component to render.

58. What is the significance of the Link component in React Router?

The Link component is used to create a hyperlink to a specific URL path in a React Router application. It allows for navigating between pages without causing a full page reload.

59. What is the significance of the NavLink component in React Router?

The NavLink component is used to create a navigation link that applies a specific style when the link is active in a React Router application. It allows for styling active links differently from other links.

60. What is the significance of the BrowserRouter component in React Router?

The BrowserRouter component is used to wrap the entire application and provide a router instance for the application in a React Router application. It allows for handling routing for the entire application.

61. What is the significance of the HashRouter component in React Router?

The HashRouter component is used to provide routing for a single-page application with a hash-based URL in a React Router application. It allows for handling routing for a single-page application with client-side rendering.

62. What is the significance of the MemoryRouter component in React Router?

The MemoryRouter component is used to provide routing for a non-DOM environment in a React Router application. It allows for handling routing in non-DOM environments like testing or server rendering.

63. What is the significance of the StaticRouter component in React Router?

The StaticRouter component is used to provide routing for server-side rendering in a React Router application. It allows for handling routing for server-rendered applications.

64. What is the significance of the Prompt component in React Router?

The Prompt component is used to display a prompt message when a user attempts to navigate away from a page in a React Router application. It allows for preventing accidental navigation and prompting the user to confirm before leaving a page.

65. What is the significance of the RouteConfig component in React Router?

The RouteConfig component is used to define multiple routes in a single configuration object in a React Router application. It allows for defining routes in a more organized and readable way.

66. What is the difference between controlled and uncontrolled components in React?

In a controlled component, the value of the component is controlled by the React state, and any changes to the value trigger a state update. In an uncontrolled component, the value of the component is controlled by the DOM, and changes to the value are not tracked by React.

67. What is the significance of the ref attribute in React?

The ref attribute is used to access the underlying DOM node or React component instance for a given element in a React application. It allows for manipulating the DOM or interacting with child components imperatively.

68. What are React fragments?

React fragments are a way to group a list of child elements without adding an additional DOM element to the page. They are declared using the <></> syntax or the <React.Fragment> component.

69. What is the significance of the key attribute in React?

The key attribute is used to uniquely identify child elements in a list of elements rendered by a React component. It allows for efficient updates to the list without having to re-render all the elements.

70. What is the significance of the dangerouslySetInnerHTML attribute in React?

The dangerouslySetInnerHTML attribute is used to set the inner HTML of an element in a React application. It should be used with caution as it can potentially expose the application to cross-site scripting (XSS) attacks.

71. What are higher-order components in React?

Higher-order components are functions that take a component as input and return a new component with additional functionality. They are used to share code between multiple components or to add cross-cutting concerns like authentication or data fetching.

72. What is the significance of the context API in React?

The context API is a way to pass data down the component tree without having to manually pass props down to every component. It allows for creating a shared state that can be accessed by any component in the tree.

73. What are React hooks?

React hooks are functions that allow for adding state and lifecycle methods to functional components in a React application. They were introduced in React 16.8 as a way to simplify component logic and reduce code duplication.

74. What are the rules of hooks in React?

The rules of hooks in React state that hooks can only be called at the top level of a functional component or another custom hook. They should not be called inside loops, conditions, or nested functions.

75. What is the significance of the useEffect hook in React?

The useEffect hook is used to add side effects to a React functional component. It allows for performing actions like data fetching, subscribing to events, or manipulating the DOM after the component has been rendered.