[Updated] 300+ React Js Interview (MCQ) With Answers - April 2024

Most Asked 300+ React Js Interview Multiple Choice Questions With Answers

1. What is the use of the create-react-app command?

1. Updates a React app.
2. Creates a new React app.
3. Installs dependencies.
4. None of the above.

npm update react-scripts
or 
yarn upgrade react-scripts

2. What keyword initiates a class in JavaScript?

1. Constructor
2. Class
3. Object
4. DataObject

3. What does ES6 stand for?

1. ECMAScript 6
2. ECMA 6
3. ECMAJavaScript 6
4. EJavaScript 6

4. What will be the output of the following JSX code?

const name = "John";
const element = <h1> Hello, {name}! </h1>

1. "Hello, John!"
2. "Hello, {name}!"
3. The code will throw an error.
4. None of the above.

5. What is the correct name of React.js?

1. React
2. React.js
3. ReactJS
4. All of the above

6. Which advantage does JSX provide?

1. Enables server-side rendering.
2. Reduces the size of the React.js library.
3. Simplifies code readability and writing.
4. Automatically handles state management.

7. What is ReactJS?

1. A programming language
2. A framework for building user interfaces
3. A database management system
4. An operating system

8. What command is used to install create-react-app globally?

1. npm install -g create-react-app
2. npm install create-react-app
3. npm install -f create-react-app
4. install -g create-react-app

9. What serves as input for class-based components in React?

1. Class
2. Factory
3. Render
4. Props

10. Why should component names start with capital letter?

1. To differentiate from regular HTML tags.
2. To make it easier to distinguish between components and elements.
3. Both A and B are correct.
4. None of the above.

11. Which method is used to render a React element into the DOM

1. React.createElement()
2. componentDidMount()
3. renderToDOM()
4. ReactDOM.render()

12. What is the output of the following code snippet?

import React from 'react';

function App() {
  return (
    <div>
      <h1>Hello World!</h1>
      <p>This is a React app.</p>
    </div>
  );
}

export default App;

1. It renders a div element with a heading and paragraph inside.
2. It throws an error.
3. It renders nothing.
4. None of the above.

13. What is the purpose of the "key" prop in React.js?

1. "Key" prop is used to look pretty, and there is no benefit whatsoever.
2. "Key" prop is a way for React to identify a newly added item in a list and compare it during the "diffing" algorithm.
3. It is one of the attributes in HTML.
4. It is not commonly used in an array.

const fruits = ['apple', 'banana', 'cherry'];

const fruits = [
        { id: 1, name: 'apple' },
        { id: 2, name: 'banana' },
        { id: 3, name: 'cherry' }
      ];

<ul>
	{fruits.map(fruit => (
     <li key={fruit.id}>{fruit.name}</li>
     ))}
</ul>

14. What will be the output of the following JSX code?

const element = <button onClick={() => alert("Button clicked!")}>Click me</button>

1. A button with the text "Click me" that triggers an alert when clicked.
2. A syntax error due to the arrow function syntax.
3. A warning about the missing onClick handler.
4. None of the above.

15. Which of the following is a valid React Component?

A.

const myComponent = () => { return <h1>Hello World!</h1> }

B.

class MyComponent extends React.Component { render() { return <h1>Hello World!</h1> } }

1. A
2. B
3. Both A and B
4. None of the above

16. When was React.js initially released?

1. May 29, 2013
2. April 29, 2013
3. June 29, 2013
4. May 29, 2014

17. What is the virtual DOM in React.js used for?

1. Handling user authentication
2. Creating database queries
3. Improving performance by minimizing DOM manipulation
4. Styling React components

18. What is the purpose of the PureComponent class?

1. To create a component that automatically implements shouldComponentUpdate() for improved performance.
2. To create a component that does not implement shouldComponentUpdate() for simpler code.
3. To create a component that does not require state management.
4. None of the above.

19. Difference between react-router-dom and react-router-native?

1. react-router-dom is used for web applications, while react-router-native is used for mobile applications.
2. react-router-native is used for web applications, while react-router-dom is used for mobile applications.
3. react-router-dom and react-router-native are the same thing.
4. None of the above.

20. What is the output of the following React code snippet?

import React from 'react';
import ReactDOM from 'react-dom';

class App extends React.Component {
    render() {
         return <h1>Hello World!</h1>
    }
}
ReactDOM.render(<app>, document.getElementById('root'));

1. It renders a heading element with the text "Hello World!" to the root element of the HTML document.
2. It throws an error.
3. It renders nothing.
4. None of the above.

21. What is the primary benefit of virtual DOM in terms of performance optimization?

1. It eliminates the need for the actual DOM, reducing memory usage.
2. It completely eliminates the need for re-rendering components.
3. It reduces the time it takes to fetch data from an API.
4. It minimizes the number of updates required to the actual DOM.

22. How to write comments in React?

1. Use single-line comments //
2. Use multi-line comments /* /
3. Use JSX comments {/ */}
4. All of the above

import React from 'react';

function UserProfile({ username, bio }) {
  // This component displays a user's profile information.

  // Single-line comment: Here, we receive the username and bio as props.

 return (
    <div className="user-profile">
      {/* JSX comment: This div holds the user's profile information. */}
       <h2>Welcome, {username}! </h2>
      {
        /*
          Multi-line comment: Inside the div, we display the user's
          username and bio.
        */
      }
      <p>{bio}</p>
     </div>
  );
}

export default UserProfile;

23. What are the ways to handle data in react.js?

1. state and services
2. state and component
3. state and props
4. services and component

24. Does React.js cover only the view layer of the app?

1. Yes
2. No

25. What is the output of the following code snippet?

import React from 'react';
  
function Greeting(props) {
    return <h1>Hello, {props.name}!</h1>
}

export default Greeting;

1. It defines a functional component that displays a greeting.
2. It defines a class component that displays a greeting.
3. It defines a higher-order component that displays a greeting.
4. None of the above.

26. Babel is a:

1. Compiler
2. Transpiler
3. Both A and B are correct
4. None of the above

27. Which of the following statements is true for controlled components?

1. The source of truth is DOM.
2. The source of truth can be anything.
3. The source of truth is a component state.
4. None of the above.

28. What is the term used to describe the process of converting ES6 (modern JavaScript) code into ES5 (older JavaScript) using Babel.js?

1. ES6ification
2. Transpilation
3. Optimization
4. Compilation

29. What is wrong with the following JSX code?

const element = <p class="red-text">This text should be red.</p>

1. The class prop should be className in JSX.
2. The class prop should be style in JSX.
3. The class prop is not a valid prop for the <p> element.
4. None of the above.

30. What is the render() method in a React Component?

1. A method that returns a React element
2. A method that returns a DOM node
3. A method that updates the state of a component
4. None of the above

31. What is wrong with the following JSX code?

const element = <img src="image.png" />

1. The img element is missing a closing tag.
2. The src prop is not enclosed in quotes.
3. The src prop should be source in JSX.
4. None of the above.

32. What is the output of the following React code snippet?

import React from 'react';
import ReactDOM from 'react-dom';

function App() {
    return <h1>Hi</h1>
}

ReactDOM.render(, document.getElementById('root'));

1. It renders a heading element with the text "Hi" to the root element of the HTML document.
2. It throws an error.
3. It renders nothing.
4. None of the above.

33. Which of the following statements about React's rendering process is true?

1. React always renders components synchronously in the order they are called.
2. React uses a single rendering thread for all components.
3. React may batch multiple component updates for performance reasons.
4. React renders components in parallel with the main application thread.

34. What is the purpose of setState() in React.js?

1. Invoke code after the setState operation is done.
2. Replace the state completely instead of the default merge action.
3. Access the previous state before the setState operation.
4. None of the above.

import React, { useState } from 'react';

function ExampleComponent() 
    const [message, setMessage] = useState('Initial Message');

    const handleClick = () => {
    // Using setMessage to change the message
    setMessage('Updated Message');
    };

    return (
        <div>
           <p>{message} </p>
           <button onClick={handleClick}>Change Message </button>
         </div>
      );
    }

export default ExampleComponent;

35. What will happen if you remove the 'ReactDOM.render' call from the given React code snippet?

import React from 'react';
import ReactDOM from 'react-dom';
 function App() {
   return <h1>Hello World!</h1>;
 }
// ReactDOM.render(<App />, document.getElementById('root'));

1. It will render nothing, and the page will be empty.
2. It will result in a compilation error.
3. It will still render the 'Hello World!' heading to the page.
4. It will throw a runtime error.

36. What are props in React and how are they used?

1. Methods
2. Injected
3. Both 1 & 2
4. All of the above

37. How many ways can you define variables in ES6?

1. 1
2. 3
3. 4
4. 5

38. How does React.js optimize performance when updating the user interface?

1. By directly manipulating the original DOM elements.
2. By using a lightweight representation of the actual DOM called the Virtual DOM.
3. By relying on browser-specific optimizations for rendering.
4. By increasing the size of the React.js library to handle updates more efficiently.

39. How many elements can a valid React component return?

1. 1
2. 2
3. 4
4. 5

40. What is the purpose of the constructor() method in a class component?

1. Define the initial state
2. Define structure and content
3. Define lifecycle methods
4. None of the above

41. What is the purpose of the ReactDOM.render() method?

1. Render a React component to the DOM
2. Create a new React component
3. Update the state of a React component
4. None of the above

42. What is the output of the following code snippet?

import React, { useState } from 'react';
function Counter() {
    const [count, setCount] = useState(0);
    const handleClick = () => {
        setCount(count + 1);
    }
    return (
        <div>
           <p>You clicked {count} times.</p>
          <button onClick={handleClick}>Click me</button>
        </div>
    );
}

export default Counter;

1. Defines a class component with an incrementable counter
2. Defines a functional component with an incrementable counter
3. Defines a higher-order component with an incrementable counter
4. None of the above.

43. How can you set a default value for an uncontrolled form field?

1. Using Value property
2. using the defaultValue property
3. Using the default property
4. It is assigned automatically.

44. What is the smallest building block of ReactJS?

1. Props
2. Elements
3. Components
4. None of the above

45. In a component hierarchy, if a parent component passes a prop to a child component, can the child component modify the value of that prop directly?

1. Yes, a child component can modify the value of a prop directly.
2. No, a child component cannot modify the value of a prop directly.
3. It depends on whether the prop is marked as mutable or immutable.
4. Only if the parent component explicitly allows it.

46. Purpose of create-react-app tool?

1. Create a new React project with preconfigured settings
2. Create a new React component
3. Create a new Redux store
4. None of the above

47. What is the function used to change the state of the component?

1. this.setState
2. this.setChangeState
3. this.State{}
4. None of the above.

48. Two primary ways to manage data

1. State & Props
2. Services & Components
3. State & Services
4. State & Component

49. Difference between a controlled component and an uncontrolled component

1. A controlled component uses state to manage its data, while an uncontrolled component does not.
2. An uncontrolled component uses state to manage its data, while a controlled component does not.
3. Controlled components and uncontrolled components are the same thing.
4. None of the above.

50. What is the output of the following React code snippet?

import React, { Component } from 'react';

class Counter extends Component {
	constructor() {
		super();
		this.state = {
		count: 0
		};
	}

	handleIncrement = () => {
		this.setState({ count: this.state.count + 1 });
	};

	render() {
	return (
		<div>
		<p>You clicked {this.state.count} times.</p>
		<button onClick={this.handleIncrement}>Click me</button>
		</div>
	);
	}
}

export default Counter;

1. Functional component with an incrementable counter.
2. Class component with an incrementable counter.
3. Higher-order component with an incrementable counter.
4. None of the above.

51. In a class component, what method is used to update the state based on the previous state?

1. Using this.props
2. Using setState()
3. Using this.state
4. Using state.update()

52. What is the output of the following code snippet?

import React from 'react';
class Greeting extends React.Component {
   render() {
    return <h1>Hello, {this.props.name}!</h1>;
  }
}

export default Greeting;

1. Class component displaying a greeting.
2. Functional component displaying a greeting.
3. Higher-order component displaying a greeting.
4. None of the above.

53. How do you define a functional component?

1. Extend React.Component class
2. Use the class keyword
3. Define a function returning JSX element
4. Use the render() method

54. How do you define a class component?

1. Extend React.Component class
2. Use the class keyword
3. Define a function returning JSX
4. Use the render() method

55. What does "state" represent?

1. A permanent storage
2. Internal storage of the component
3. External storage of the component
4. None of the above

56. What is the declarative method for rendering a list of components based on an array's values?

1. Using the reduce array method
2. Using the <Each /> component
3. Using the Array.map() method
4. With a for/while loop

57. What is the output of the following code snippet?

import React from 'react';
import ReactDOM from 'react-dom';
class App extends React.Component {
    render() {
        return <h1>Hello World!</h1>
    }
}

ReactDOM.render(, document.getElementById('root'));

1. Renders "Hello World!" in a heading to the root HTML element.
2. Throws an error.
3. Renders nothing.
4. None of the above.

58. What is the default port for the webpack-dev-server?

1. 3000
2. 8080
3. 3030
4. 6060

59. Which keyword is used for class inheritance in JavaScript?

1. Create
2. Inherits
3. Extends
4. This

60.Difference between stateful and stateless components

1. Stateful components have state while stateless components do not have state.
2. Stateful components use class components while stateless components use functional components.
3. Stateful components have lifecycle methods while stateless components do not have lifecycle methods.
4. Stateful components are used for rendering dynamic data while stateless components are used for rendering static data.

61. Which of the following statement is true for uncontrolled components in React.js?

1. The source of truth is a component state.
2. The source of truth can be anything.
3. The source of truth is DOM.
4. None of the above.

62. What is the output of the following React code snippet?

import React from 'react';
import PropTypes from 'prop-types';
function Greeting(props) {
  return <h1>Hello, {props.name}!</h1>;
}

Greeting.propTypes = {
  name: PropTypes.string.isRequired
};

export default Greeting;

1. It defines a functional component that displays a greeting.
2. It defines a class component that displays a greeting.
3. It defines a higher-order component that displays a greeting.
4. None of the above.

63. What happens when the state of a React component is changed?

1. It will do nothing; you have to call render method to render the component again.
2. It will re-render the component.
3. It can be created again from scratch.
4. None of the above.

64. Calls to setState() method in React.js are:

1. Synchronous in nature.
2. Asynchronous in nature.
3. Are asynchronous but can be made synchronous when required.
4. None of the above.

65. Which keyword is used to create a class inheritance in React?

1. This
2. Create
3. Extends
4. Inherits

66. What helps React for keeping their data unidirectional?

1. JSX
2. Flux
3. DOM
4. Props

67. What is the correct data flow sequence in the Flux architecture pattern?

1. Dispatcher->Action->Store->View
2. Action->Dispatcher->View->Store
3. Action->Dispatcher->Store->View
4. Action->Store->Dispatcher->View

68. What are the requirements for the keys given to a list of elements in React?

1. Do not require to be unique
2. Unique in the DOM
3. Unique among the siblings only
4. All of the above

69. How can you access the state of a component from inside of a member function?

1. this.getState()
2. this.values
3. this.prototype.stateValue
4. this.state

70. What is used in React.js to increase performance?

1. Virtual DOM
2. Original DOM
3. Both original and virtual DOM
4. None of the above

71. What is a state in React.js?

1. A permanent storage
2. An internal storage of the component
3. An external storage of the component
4. All of the above

72. Where are React.js components typically stored?

1. Inside the js/components/ directory
2. Inside the vendor/components/ directory
3. Inside the external/components/ directory
4. Inside the vendor/ directory

73. What happens if the key attribute is not provided when looping through an array in JSX?

1. The code will not compile.
2. React will automatically assign a default key to each element.
3. Each element will have the same key, causing rendering issues.
4. The element will not be rendered.

74. How many elements can a valid React component return?

1. 2
2. 3
3. 1
4. 4

75. How can a React app be created?

1. install -g create-react-app
2. npm install create-react-app
3. npx create-react-app reactapp
4. None of the above

76. What is the purpose of Babel in JavaScript development?

1. A JavaScript transpiler
2. A JavaScript interpreter
3. A JavaScript compiler
4. None of the above

77. What is the purpose of the key attribute when looping through an array in JSX?

1. To assign a unique identifier to each element.
2. To change the order of elements in the array.
3. To group elements together based on a shared property.
4. To apply styles to individual elements.

78. What is the output of the following React code snippet?

import React from 'react';
class Counter extends React.Component {
constructor(props) {
    super(props);
    this.state = { count: 0 };
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    this.setState({ count: this.state.count + 1 });
  }

  render() {
    return (
      <div>
        <p>You clicked {this.state.count} times.</p>
        <button onClick={this.handleClick}>Click me</button>
      </div>
    );
  }
}

export default Counter;

1. It defines a class component that displays a counter that can be incremented using a button.
2. It defines a functional component that displays a counter that can be incremented using a button.
3. It defines a higher-order component that displays a counter that can be incremented using a button.
4. None of the above.

79. In which programming language is React.js written?

1. JavaScript
2. Python
3. Java
4. Php

80. Which of the following React code snippets will render a component that displays a list of names from an array of strings?

A.

function NameList(props) {
        const names = props.names;
        const listItems = names.map((name) =>
          <li>{name}</li>
        );
        return (
          <ul>{listItems}</ul>
        );
 }
ReactDOM.render(
        <NameList names={['Alice', 'Bob', 'Charlie']} />,
        document.getElementById('root')
);

B.

function NameList(props) {
        const names = props.names;
        const listItems = names.map((name) =>
          <li>{name}</li>
        );
        return (
          <ul>{listItems}</ul>
        );
}
ReactDOM.render(
        <NameList names={["Alice", "Bob", "Charlie"]} />,
        document.querySelector("#root")
);

C.

class NameList extends React.Component {
        render() {
          const names = this.props.names;
          const listItems = names.map((name) =>
            <li>{name}</li>
          );
          return (
            <ul>{listItems}</ul>
          );
        }
}
ReactDOM.render(
    <NameList names={["Alice", "Bob", "Charlie"]} />,
    document.getElementById('root')
);

D.

class NameList extends React.Component {
        render() {
          const names = this.props.names;
          const listItems = names.map((name) =>
            <li>{name}</li>
          );
          return (
            <ul>{listItems}</ul>
          );
        }
}
ReactDOM.render(
    <NameList names={['Alice', 'Bob', 'Charlie']} />,
    document.querySelector('#root')
);

1. A
2. B
3. C
4. D

81. How do you add a key to each element when looping through an array in JSX?

1. Use the index of the element as the key.
2. Use a unique identifier as the key.
3. Keys are not necessary when looping through an array in JSX.
4. Use a random number generator to create a key.

82. How do you import a named export from a module in React?

1. import NamedExport from './Module';
2. import { NamedExport } from './Module';
3. import * as NamedExport from './Module';
4. import { name as NamedExport } from './Module';

83. How do you export a component as a named export in a React module?

1. export MyComponent from './MyComponent';
2. export { MyComponent };
3. module.exports = { MyComponent };
4. export default MyComponent;

84. How do you export a component as the default export in a React module?

1. export default MyComponent;
2. export MyComponent from './MyComponent';
3. export { MyComponent };
4. module.exports = MyComponent;

85. What is the correct syntax for importing a default export from a module in React?

1. import DefaultComponent from './Component';
2. import { DefaultComponent } from './Component';
3. import * as DefaultComponent from './Component';
4. import { default } from './Component';

86. Which API must every React.js component include?

1. SetinitialComponent
2. renderComponent
3. render
4. All of the above

87. In the context of the MVC pattern, what role does React.js play?

1. Middleware
2. Controller
3. Model
4. View

88. Who originally developed React.js?

1. Jordan Walke
2. Rasmus Lerdorf
3. Miško Hevery
4. None of the above

89. How can we pass data to a component from outside in React.js?

1. SetState
2. Render with arguments
3. Props
4. PropTypes

90. Which of the following lifecycle events do React components have at the highest level?

1. Destruction Initialization State/Property Updates
2. Initialization State/Property Updates Destruction
3. State/Property Updates Initialization Destruction
4. All of the above

91. Which of the following methods is not a part of ReactDOM in React.js?

1. ReactDOM.destroy()
2. ReactDOM.hydrate()
3. ReactDOM.createPortal()
4. ReactDOM.findDOMNode()

92. In which of the following condition, the React.js Lifecycle method static getDerivedSateFromProps(props, state) is called?

1. The component is created for the first time.
2. The state of the component is updated.
3. Both of the above.
4. None of the above.

93. What is the purpose of the shouldComponentUpdate method in ReactJS?

1. It is used to update the component's state.
2. It is used to determine whether the component should be re-rendered.
3. It is used to handle user input events.
4. It is used to fetch data from an external API.

94. What is the useLayoutEffect() function used for in React?

1. Completing the update
2. Optimizing for all devices
3. Changing the layout of the screen
4. When we need the browser to paint before effects

95. Which method is used to update a component every second in React?

1. componentDidUpdate()
2. shouldComponentUpdate()
3. componentDidMount()
4. setInterval()

96. What is the purpose of state in React?

1. To store data that can be changed within the component
2. To pass data from a parent component to a child component
3. To render HTML content in the component
4. None of the above

97. Does React.js create a virtual DOM in memory?

1. TRUE
2. FALSE
3. Can be true or false
4. Cannot say

98. What is the difference between Imperative and Declarative in ReactJS?

1. Imperative is used for describing how the UI should be updated while declarative is used for describing what the UI should look like.
2. Imperative is used for describing what the UI should look like while declarative is used for describing how the UI should be updated.
3. Imperative is used for passing data between components while declarative is used for managing component state.
4. Imperative is used for handling user input events while declarative is used for rendering static data.

99. How to perform automatic redirect after login in React?

1. Use the history prop to redirect the user.
2. Use the setState method to update the page.
3. Use the location prop to redirect the user.
4. Use the Router component to redirect the user.

100. What method can be used to loop through an array in JSX?

1. for-loop
2. map()
3. forEach()
4. while-loop

101. What is the syntax for looping through an array in JSX?

1. {for (let i = 0; i < array.length; i++) {}}
2. {array.forEach((item) => {})}
3. {array.map((item) => {})}
4. {while (i < array.length) {}}

102. What is the purpose of using StrictMode in React?

1. To enforce best practices and detect potential problems.
2. To disable warnings and errors in the console.
3. To optimize the rendering performance.
4. None of the above.

103. Which of the following is not a limitation of React?

1. React can be difficult to learn for beginners.
2. React has a steep learning curve.
3. React applications can be slower than traditional server-side applications.
4. React can be hard to integrate with other technologies.

104. Which of the following is a limitation of React?

1. React can only be used for client-side rendering.
2. React does not support server-side rendering.
3. React is not suitable for large-scale applications.
4. React does not have built-in support for animations.

105. How do you validate an object with specific properties in React?

1. Use the object validator
2. Use the shape validator
3. Use the arrayOf validator
4. Objects are automatically validated in React

106. Which of the following is not a valid PropTypes validator for a boolean prop in React?

1. bool
2. number
3. oneOf
4. oneOfType

107. Which method in React.js refers to the parent class?

1. inherits()
2. self()
3. super()
4. this()

108. What is the result of rendering an input element with disabled={false} in React.js?

1. It will be rendered as disabled.
2. It will not be rendered at all.
3. It will be rendered as enabled.
4. You cannot set it false.

109. What is the purpose of the ReactJS Context API?

1. It is used to pass data between components
2. It is used to manage the component's state
3. It is used to handle user input events
4. It is used to fetch data from an external API

110. What is the purpose of the "webpack" command in React.js?

1. To transpile JavaScript into one file
2. To run the local development server
3. To bundle modules
4. None of the above

111. What is reconciliation in ReactJS?

1. The process of comparing and updating the virtual DOM
2. The process of comparing and updating the real DOM
3. The process of comparing and updating the state of a component
4. The process of comparing and updating the props of a component

112. When does reconciliation occur in ReactJS?

1. When a component's state changes
2. When a component's props change
3. When a component mounts or unmounts
4. All of the above

113. Which algorithm does ReactJS use for reconciliation?

1. Breadth-first search
2. Depth-first search
3. Merge sort
4. Quick sort

114. What happens when two components have the same key in ReactJS?

1. ReactJS merges the two components into one.
2. ReactJS throws an error.
3. ReactJS updates the first component with the properties of the second component.
4. ReactJS updates the second component with the properties of the first component.

115. Which method is used to compare two React elements in the reconciliation process?

1. shouldUpdate()
2. componentWillUpdate()
3. componentDidUpdate()
4. render()

116. What is the difference between "shallow" and "deep" rendering in React testing?

1. Shallow rendering only renders the top-level component, while deep rendering renders all child components as well.
2. Shallow rendering only renders the virtual DOM, while deep rendering renders the real DOM.
3. Shallow rendering only renders components that have been updated since the previous render, while deep rendering renders all components.
4. There is no difference between shallow and deep rendering in React testing.

117. What is a limitation of using React with server-side rendering?

1. Server-side rendering can increase the load time of the application.
2. Server-side rendering can make the application less scalable.
3. Server-side rendering can cause compatibility issues with certain browsers.
4. Server-side rendering can make it harder to debug the application.

118. Which hook in React can be used to share state between components?

1. useMemo
2. useCallback
3. useEffect
4. useContext

119. Which hook in React can be used to memoize a function?

1. useMemo
2. useCallback
3. useEffect
4. useState

120. The useEffect hook in React can be used to subscribe to events. Which cleanup function should be returned to unsubscribe?

1. removeEventListener
2. clearInterval
3. clearTimeout
4. off

121. Which hook in React can be used to optimize performance by preventing unnecessary renders?

1. useMemo
2. useCallback
3. useEffect
4. useContext

122. In the useEffect hook, the second argument is used to specify:

1. The callback function to execute
2. The dependencies to watch for changes
3. The initial state of the component
4. The time interval for the effect to run

123. What is the purpose of the useContext hook in React?

1. To share state between components without using props.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

124. What is the purpose of the useCallback hook in React?

1. To memoize a function to prevent unnecessary re-renders.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

125. What is the purpose of the useEffect hook in React?

1. To perform side effects after rendering a component.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

126. What is the purpose of the useLayoutEffect hook in React?

1. To perform side effects before rendering a component.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

127. What is the difference between useMemo and useCallback hooks in React?

1. useMemo is used for memoizing values, while useCallback is used for memoizing functions.
2. useCallback is used for memoizing values, while useMemo is used for memoizing functions.
3. useMemo and useCallback are the same thing.
4. None of the above.

128. What is the purpose of the useRef hook in React?

1. To create a mutable reference to a value that persists across renders.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

129. What is the purpose of the useImperativeHandle hook in React?

1. To expose a component's imperative API to its parent component.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

130. What is the purpose of the useDebugValue hook in React?

1. To display custom labels in the React DevTools.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

131. What is the purpose of the useTransition hook in React?

1. To defer rendering of a component until after a certain time has elapsed.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

132. What is the purpose of the useSubscription hook in React?

1. To subscribe to an external event source and update the state accordingly.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

133. What is the purpose of the useIntersect hook in React?

1. To observe when an element intersects with the viewport and update the state accordingly.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

134. Which library is used for routing in React applications?

1. React Router
2. Redux
3. Axios
4. Lodash

135. What is React Router?

1. A library for handling server-side routing in React
2. A library for handling client-side routing in React
3. A library for styling in React
4. None of the above

136. Which component is used to render a Route in React Router?

1. BrowserRouter
2. Route
3. Link
4. Switch

137. How do you pass parameters in React Router?

1. As query strings
2. As URL parameters
3. As state variables
4. None of the above

138. How can you implement a default or NotFound page using React Router?

1. Use the component.
2. Use the component.
3. Use the component.
4. Use the component.

139. Which of the following is an advantage of using React Router?

1. Improved performance
2. Improved user experience
3. Improved SEO
4. All of the above

140. What is the purpose of the React Router library?

1. To provide a way to handle routing in React applications.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

141. How do you redirect to a new route in React Router?

1. By using the Redirect component
2. By using the Route component with the "redirect" attribute
3. By using the Switch component with the "redirect" attribute
4. None of the above

142. Which of the following is NOT a type of routing provided by React Router?

1. Client-side routing
2. Server-side routing
3. Static routing
4. Dynamic routing

143. Which component is used to create a nested route in React Router?

1. BrowserRouter
2. Route
3. Link
4. Switch

144. Which component is used to create a link in React Router?

1. BrowserRouter
2. Route
3. Link
4. Switch

145. Which of the following is NOT a type of router provided by React Router?

1. BrowserRouter
2. HashRouter
3. MemoryRouter
4. HttpRouter

146. What is the purpose of the Switch component in React Router?

1. To render multiple components based on the current route.
2. To render a single component based on the current route.
3. To handle user authentication in React Router.
4. None of the above.

147. What is the difference between a Route component and a NavLink component in React Router?

1. A Route component is used to render a component based on the current route, while a NavLink component is used to create links to different routes.
2. A NavLink component is used to render a component based on the current route, while a Route component is used to create links to different routes.
3. Route components and NavLink components are the same thing.
4. None of the above.

148. What is the purpose of the withRouter higher-order component in React Router?

1. To connect a component to the Redux store.
2. To enable access to the history object in a component.
3. To create a new component in React Router.
4. None of the above.

149. What is the purpose of the Redirect component in React Router?

1. To redirect the user to a different route.
2. To render a component based on the current route.
3. To handle user authentication in React Router.
4. None of the above.

150. What is the purpose of the Prompt component in React Router?

1. To prompt the user before navigating to a different route.
2. To render a component based on the current route.
3. To handle user authentication in React Router.
4. None of the above.

151. What is the difference between the BrowserRouter and HashRouter components in React Router?

1. BrowserRouter uses browser history, while HashRouter uses hash history.
2. HashRouter uses browser history, while BrowserRouter uses hash history.
3. BrowserRouter and HashRouter are the same thing.
4. None of the above.

152. What is the purpose of the Link component in React Router?

1. To render a component based on the current route.
2. To create links to different routes.
3. To handle user authentication in React Router.
4. None of the above.

153. What is the difference between the exact and strict props in a Route component in React Router?

1. exact checks for an exact match of the URL path, while strict checks for a trailing slash.
2. strict checks for an exact match of the URL path, while exact checks for a trailing slash.
3. exact and strict are the same thing.
4. None of the above.

154. What is the purpose of the NavLink component in React Router?

1. To create links to different routes.
2. To render a component based on the current route.
3. To handle user authentication in React Router.
4. None of the above.

155. What is the purpose of the withRouter higher-order component in React Router?

1. To provide access to the history, location, and match props in any component.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

156. What is the purpose of the useLocation hook in React Router?

1. To access the current location of the app.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

157. What is the purpose of the useParams hook in React Router?

1. To access the URL parameters of the current route.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

158. What is the purpose of the useHistory hook in React Router?

1. To access the browser history object and navigate programmatically.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

159. What is the purpose of the useNavigate hook in React Router?

1. To navigate programmatically without needing access to the history object.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

160. What is the purpose of the useRouteMatch hook in React Router DOM?

1. To match the current URL to a route configuration and extract information.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

161. What does JSON stand for?

1. JavaScript Object Notation
2. Java Standard Object Notation
3. JavaScript Structured Notation
4. Java Serialized Object Notation

162. Which of the following is a valid JSON data type?

1. Date
2. Function
3. Undefined
4. All of the above

163. What is the syntax for creating an empty JSON object?

1. {}
2. []
3. ()
4. //

164. Which method is used to convert a JavaScript object to a JSON string?

1. JSON.stringify()
2. JSON.parse()
3. JSON.stringifyify()
4. JSON.parseify()

165. Which method is used to convert a JSON string to a JavaScript object?

1. JSON.stringify()
2. JSON.parse()
3. JSON.stringifyify()
4. JSON.parseify()

166. Which of the following is a valid JSON object?

1. {name:"John",age:30,city:"New York"}
2. ['name':'John','age':30,'city':'New York']
3. {"name":"John","age":30,"city":"New York"}
4. {"name"="John","age"=30,"city"="New York"}

167. Which of the following is a valid JSON array?

1. ["apple", "banana", "orange"]
2. {fruit: ["apple", "banana", "orange"]}
3. ["fruit": "apple", "fruit": "banana", "fruit": "orange"]
4. All of the above

168. What is the purpose of the useReducer hook in React?

1. To manage more complex state with a reducer function.
2. To manage simple state without a reducer function.
3. To manage state with an asynchronous function.
4. None of the above.

169. What is the difference between the useState and useReducer hooks in React?

1. useState is used for managing simple state, while useReducer is used for managing more complex state.
2. useReducer is used for managing simple state, while useState is used for managing more complex state.
3. useState and useReducer are the same thing.
4. None of the above.

170. Which of the following libraries is used to manage state in React applications?

1. Redux
2. jQuery
3. D3
4. Bootstrap

171. What is Redux?

1. A JavaScript library for building user interfaces.
2. A state management library for JavaScript applications.
3. A CSS framework for styling web pages.
4. None of the above.

172. What is a Redux store?

1. An object that holds the state of an application.
2. A function that returns the state of an application.
3. A component that renders the state of an application.
4. None of the above.

173. What is a Redux action?

1. An object that describes an event in the application.
2. A function that updates the state of the application.
3. A component that renders the state of the application.
4. None of the above.

174. What is a Redux reducer?

1. A function that updates the state of the application in response to an action.
2. A component that renders the state of the application.
3. A CSS framework for styling web pages.
4. None of the above.

175. What is the purpose of the connect function in Redux?

1. To connect a React component to the Redux store.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

176. What is the purpose of the Provider component in Redux?

1. To provide the Redux store to a React component tree.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

177. What is the purpose of the bindActionCreators function in Redux?

1. To bind action creators to the dispatch function of the Redux store.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

178. What is a Redux middleware?

1. A function that runs after a reducer is called.
2. A function that runs before a reducer is called.
3. A function that handles async actions.
4. None of the above.

179. What is the purpose of the thunk middleware in Redux?

1. To allow actions to return functions instead of objects.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

180. What is the difference between Redux and React state?

1. Redux is used for global state management, while React state is used for local state management.
2. Redux is used for local state management, while React state is used for global state management.
3. Redux and React state are the same thing.
4. None of the above.

181. What is the purpose of the Redux DevTools?

1. To debug Redux applications.
2. To design Redux applications.
3. To manage Redux state.
4. None of the above.

182. What is the purpose of the selector function in Redux?

1. To derive data from the state of the Redux store.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

183. What is the purpose of the useContext hook in Redux?

1. To provide a way to pass data through the component tree without having to pass props down manually at every level.
2. To manage complex state logic in a more concise and predictable way.
3. To update the state of a component.
4. None of the above.

184. What is the purpose of the useDispatch hook in Redux?

1. To dispatch actions to the Redux store.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

185. What is the purpose of the useSelector hook in Redux?

1. To select a subset of the state from the Redux store.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

186. What is the purpose of the combineReducers function in Redux?

1. To combine multiple reducer functions into a single reducer function.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

187. What is the purpose of the createStore function in Redux?

1. To create a Redux store object.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

188. What is the purpose of the applyMiddleware function in Redux?

1. To apply middleware to the Redux store.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

189. What is the purpose of the Redux DevTools extension?

1. To provide a UI for debugging Redux applications.
2. To update the state of the Redux store.
3. To render a component to the DOM.
4. None of the above.

190. What is the purpose of the Immutable.js library?

1. To provide a collection of immutable data structures.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

191. What is a Redux selector?

1. A function that selects a portion of the state.
2. A function that handles async actions.
3. A function that creates new components.
4. None of the above.

192. What is the purpose of the bindActionCreators function in Redux?

1. To bind action creators to the Redux store dispatch function.
2. To handle async actions in Redux.
3. To update the state of a component.
4. None of the above.

193. What is the purpose of the applyMiddleware function in Redux?

1. To apply middleware to the Redux store.
2. To handle async actions in Redux.
3. To update the state of a component.
4. None of the above.

194. What is a Redux action creator?

1. A function that returns an action object.
2. A function that returns a component.
3. A function that returns a selector.
4. None of the above.

195. What is the difference between Redux and Context API in React?

1. Redux is a separate library for state management, while Context API is built into React.
2. Redux is used for local state management, while Context API is used for global state management.
3. Redux and Context API are the same thing.
4. None of the above.

196. What is the purpose of the createSelector() function in Redux?

1. To create a selector function for the Redux state.
2. To create a reducer function for the Redux store.
3. To create an action creator function for Redux.
4. None of the above.

197. What is the purpose of the Redux Saga library?

1. To handle async actions in Redux.
2. To manage routing in a Redux app.
3. To create new components in React Redux.
4. None of the above.

198. What is the difference between a presentational component and a container component in React Redux?

1. A presentational component is used for displaying data, while a container component is used for managing data.
2. A presentational component is used for managing data, while a container component is used for displaying data.
3. A presentational component and a container component are the same thing.
4. None of the above.

199. What is the purpose of the Redux DevTools extension?

1. To help developers debug and analyze the Redux store and actions.
2. To create new components in React Redux.
3. To manage routing in a Redux app.
4. None of the above.

200. What is the difference between a Redux action and a Redux thunk?

1. A Redux action is a plain JavaScript object that describes a change to the state, while a Redux thunk is a function that allows for more complex asynchronous logic.
2. A Redux action is a function that allows for more complex asynchronous logic, while a Redux thunk is a plain JavaScript object that describes a change to the state.
3. A Redux action and a Redux thunk are the same thing.
4. None of the above

201. What is the purpose of the connect function in React Redux?

1. To connect a component to the Redux store.
2. To handle async actions in Redux.
3. To update the state of a component.
4. None of the above.

202. What is the purpose of the Provider component in React Redux?

1. To provide the Redux store to all components in a React application.
2. To handle async actions in Redux.
3. To update the state of a component.
4. None of the above.

203. What is the difference between dispatching a plain object and a function in Redux?

1. Dispatching a plain object updates the state immediately, while dispatching a function allows for more complex asynchronous logic.
2. Dispatching a function updates the state immediately, while dispatching a plain object allows for more complex asynchronous logic.
3. Dispatching a plain object and a function are the same thing.
4. None of the above.

204. What is the purpose of the createSelector() function in the Reselect library?

1. To generate selectors from the Redux state.
2. To combine multiple selectors into a single selector function.
3. To memoize selectors for performance optimization.
4. None of the above.

205. How do you use React Router with Redux?

1. By creating a new store for React Router
2. By using the react-redux-router library
3. By passing the router as a prop to each component
4. None of the above

206. What is the difference between mapDispatchToProps and mapStateToProps in React Redux?

1. mapDispatchToProps is used to map action creators to props, while mapStateToProps is used to map state to props.
2. mapDispatchToProps is used to map state to props, while mapStateToProps is used to map action creators to props.
3. mapDispatchToProps and mapStateToProps are the same thing.
4. None of the above.

207. What is the purpose of the immer library in Redux?

1. To handle routing in a Redux app
2. To handle async actions in Redux
3. To enable immutable updates to the Redux state
4. None of the above

208. What is the purpose of the Redux Toolkit?

1. To simplify the process of creating Redux applications.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

209. What is the purpose of the createAsyncThunk function in the Redux Toolkit?

1. To create an action creator that dispatches async actions.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

210. What is the purpose of the createSlice() function in Redux Toolkit?

1. To create a new slice of the Redux store.
2. To create a new component in React Redux.
3. To create a new middleware function for Redux.
4. None of the above.

211. What is the lifecycle method used to make AJAX requests in React?

1. componentWillMount()
2. componentDidMount()
3. componentWillUnmount()
4. componentDidUpdate()

212. Which method is called when a component is first initialized and before it is rendered for the first time?

1. componentDidMount()
2. componentWillMount()
3. componentWillUnmount()
4. render()

213. The useEffect hook in React can be used to replace which class lifecycle method?

1. componentWillMount
2. componentWillUpdate
3. componentDidUpdate
4. shouldComponentUpdate

214. What is the purpose of the shouldComponentUpdate() method in React?

1. To determine if a component should be updated.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

215. What is the purpose of the componentWillUnmount() method in React?

1. To clean up resources used by a component before it is removed from the DOM.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

216. Which lifecycle method is called before a component is removed from the DOM?

1. componentDidMount()
2. componentWillMount()
3. componentWillUnmount()
4. componentDidUpdate()

217. Which lifecycle method is called when a component is forced to re-render?

1. componentWillUpdate()
2. shouldComponentUpdate()
3. componentDidUpdate()
4. render()

218. Which lifecycle method is called when a component receives new props?

1. componentWillReceiveProps()
2. shouldComponentUpdate()
3. componentDidUpdate()
4. componentWillUnmount()

219. Which lifecycle method is called after a component is rendered for the first time?

1. componentDidMount()
2. componentWillMount()
3. componentWillUnmount()
4. render()

220. What is the purpose of the componentDidCatch() method in React?

1. To handle errors that occur during rendering.
2. To update the state of a component.
3. To render a component to the DOM.
4. None of the above.

221. Which lifecycle method is used to optimize performance by avoiding unnecessary re-renders?

1. shouldComponentUpdate()
2. componentWillUpdate()
3. componentDidUpdate()
4. render()

222. Which lifecycle method is used to set initial state values?

1. componentWillMount()
2. componentDidMount()
3. componentWillReceiveProps()
4. constructor()

223. Which React API method is used to render a React component to the DOM?

1. ReactDOM.render()
2. React.render()
3. ReactDOM.component()
4. React.component()

224. Which React API method is used to create a new React component?

1. React.createClass()
2. ReactDOM.render()
3. React.createElement()
4. ReactDOM.component()

225. Which React API method is used to create a new React element?

1. React.createClass()
2. ReactDOM.render()
3. React.createElement()
4. ReactDOM.component()

226. Which React API method is used to access the current state of a component?

1. this.getState()
2. this.values
3. this.prototype.stateValue
4. this.state

227. Which React API method is used to handle events in React components?

1. eventHandler()
2. handleEvent()
3. handleOnClick()
4. onClick()

228. Which React API method is used to prevent default behavior in an event handler?

1. event.preventDefault()
2. this.preventDefault()
3. event.stop()
4. this.stop()

229. Which React API method is used to create a new context object?

1. React.createContext()
2. React.Context()
3. createContext()
4. createNewContext()

230. Which React API method is used to access the context object in a component?

1. this.context()
2. this.contextValue()
3. this.prototype.contextValue
4. static contextType

231. Which React API method is used to update the component after rendering?

1. componentWillMount()
2. componentDidMount()
3. componentDidUpdate()
4. componentWillUnmount()

232. Which React API method is used to remove a component from the DOM?

1. componentWillUnmount()
2. componentDidMount()
3. componentDidUnmount()
4. willUnmount()

233. Which React API method is used to check if a component is mounted?

1. this.mounted()
2. this.isMounted()
3. this.componentMounted()
4. this.isComponentMounted()

234. Which React API method is used to force a re-render of a component?

1. this.forceUpdate()
2. this.update()
3. this.rerender()
4. this.refresh()

235. Which React API method is used to set the props of a component?

1. this.setProps()
2. this.updateProps()
3. this.modifyProps()
4. this.props()

236. Which React API method is used to get the props of a component?

1. this.getProps()
2. this.props()
3. this.retrieveProps()
4. this.accessProps()

237. Which React API method is used to set the state of a component?

1. this.setState()
2. this.modifyState()
3. this.updateState()
4. this.setComponentState()

238. Which React API method is used to get the state of a component?

1. this.componentState()
2. this.getCurrentState()
3. this.state()
4. this.retrieveState()

239. Which React API method is used to set the context of a component?

1. this.setContext()
2. this.modifyContext()
3. this.updateContext()
4. this.context()

240. Which React API method is used to get the refs of a component?

1. this.refs()
2. this.getRefs()
3. this.retrieveRefs()
4. this.componentRefs()

241. What is the purpose of the "getSnapshotBeforeUpdate" lifecycle method in ReactJS?

1. To capture information from the DOM before it is updated
2. To update the state of a component
3. To update the props of a component
4. To update the DOM of a component

242. The useEffect hook in React can be used to replace which class lifecycle method?

1. componentDidMount
2. componentWillUnmount
3. componentWillReceiveProps
4. render

243. Jest is a testing framework built by Facebook for:

1. React applications
2. Angular applications
3. Vue.js applications
4. All of the above

244. What is the command to run Jest tests?

1. npm test
2. npm run jest
3. npm start
4. npm run test

245. What is the purpose of snapshots in Jest?

1. To store test results
2. To compare HTML output
3. To generate code coverage reports
4. None of the above

246. What is the syntax for creating a Jest test suite?

1. describe()
2. it()
3. test()
4. all of the above

247. What is the purpose of the "beforeEach()" function in Jest?

1. To run code after each test case
2. To run code before each test suite
3. To run code after each test suite
4. To run code before each test case

248. What is the purpose of the "afterAll()" function in Jest?

1. To run code before each test case
2. To run code after each test case
3. To run code before each test suite
4. To run code after each test suite

249. What is the purpose of the "expect()" function in Jest?

1. To define a test case
2. To make assertions
3. To run setup code
4. To run teardown code

250. What is the purpose of the "toMatch()" function in Jest?

1. To check if a value is truthy
2. To compare strings using regular expressions
3. To check if an object contains a property
4. To compare arrays for equality

251. Which library can be used to handle date and time in React applications?

1. Moment.js
2. Lodash
3. D3
4. jQuery

252. Which library can be used for internationalization in React applications?

1. Redux
2. Lodash
3. React Intl
4. Axios

253. Which library can be used for testing React components?

1. Enzyme
2. jQuery
3. Axios
4. Moment.js

254. Which library can be used for state management in React applications instead of Redux?

1. MobX
2. Axios
3. jQuery
4. Lodash

255. Which library can be used for data visualization in React applications?

1. React Motion
2. D3.js
3. Moment.js
4. React Router

256. What is the recommended library for internationalization in React?

1. i18n.js
2. react-i18next
3. react-intl
4. Both A and B

257. What is the purpose of the FormattedMessage component in react-intl?

1. to translate text messages
2. to format numbers
3. to format dates and times
4. to format currency values

258. Which component from react-intl can be used to format dates and times?

1. FormattedDate
2. FormattedTime
3. FormattedDateTime
4. FormattedMessage

259. Which function from react-intl can be used to get the user's locale?

1. getIntl
2. getLocale
3. getUserLocale
4. IntlProvider

260. What is the purpose of the "toBe()" function in Jest?

1. To check if a value is truthy
2. To compare strings using regular expressions
3. To check if an object contains a property
4. To compare values for strict equality

261. Which library can be used for server-side rendering in React applications?

1. Next.js
2. React Motion
3. Lodash
4. Axios

262. Which library can be used for managing forms in React applications?

1. Formik
2. React Motion
3. Moment.js
4. Redux

263. Which package is commonly used for animation in React?

1. react-transition-group
2. react-router
3. redux
4. axios

264. Which of the following properties can be used to create staggered animations with react-transition-group?

1. delay
2. duration
3. transitionTime
4. None of the above

265. Which method in react-transition-group is used to animate components when they mount?

1. CSSTransition
2. Transition
3. animateOnMount
4. None of the above

266. Which animation library can be used with React for more advanced animations?

1. GreenSock
2. jQuery
3. Animate.css
4. Bootstrap

267. Which library can be used for data visualization in React applications?

1. React Motion
2. D3.js
3. Moment.js
4. React Router

268. What is the purpose of the React Spring library?

1. To create smooth animations and transitions in React
2. To create responsive and mobile-friendly UIs in React
3. To manage state in React applications
4. None of the above

269. What is a fragment in React?

1. A special type of component
2. A way to group multiple elements without adding extra nodes to the DOM
3. A way to render elements outside the component tree
4. A way to add comments to the component tree

270. What is PropTypes in React?

1. A built-in method to validate props
2. A library for working with JavaScript types
3. A tool for unit testing React components
4. A way to handle errors in React components

271. Which of the following is not a valid PropTypes validator in React?

1. string
2. array
3. function
4. objectOfNumber

272. How do you specify a required prop in React?

1. Use the isRequired validator
2. Use the isRequiredProp keyword
3. Use the required attribute
4. Required props are automatically validated in React

273. How do you specify a default value for a prop in React?

1. Use the default keyword
2. Use the defaultValue keyword
3. Use the defaultProp attribute
4. Default props are automatically set in React

274. Which of the following is not a valid PropTypes validator for a function prop in React?

1. func
2. shape
3. instanceOf
4. oneOfType

275. How do you validate an array of a specific type in React?

1. Use the arrayOf validator
2. Use the instanceOf validator
3. Use the shape validator
4. Arrays are automatically validated in React

276. Which of the following is a limitation of React when it comes to testing?

1. React does not have built-in testing capabilities.
2. React testing can be difficult to set up and configure.
3. React tests can be slow to run.
4. React tests can be prone to false positives.

277. In React, the error boundaries are used to handle errors that occur in which of the following?

1. Render methods
2. Constructor methods
3. Lifecycle methods
4. All of the above

278. Which of the following is the correct way to catch errors in React?

1. Using try-catch blocks
2. Using error boundaries
3. Using conditional statements
4. Using promises

279. Which of the following is the correct way to handle errors in React?

1. By ignoring the errors
2. By logging the errors to the console
3. By displaying a user-friendly error message
4. None of the above

280. In React, what is the purpose of the error object that is passed to the componentDidCatch method?

1. To provide information about the error that occurred
2. To provide a stack trace of the error
3. To provide a way to retry the rendering of the component
4. None of the above

281. What is the best practice for handling errors in React?

1. To use error boundaries
2. To use try-catch blocks
3. To ignore the errors
4. To log the errors to the console

282. In React, what is the purpose of the error boundary component?

1. To catch and handle errors that occur in child components
2. To catch and handle errors that occur in parent components
3. To prevent errors from occurring in the first place
4. None of the above

283. How can you automatically format code using Prettier in a React project when saving files in the editor? 

1. Prettier does not support automatic formatting on file save in React projects.
2. Prettier automatically formats code on file save without any additional configuration.
3. Prettier can be configured to format code on file save by using the `.prettierignore` file.
4. Prettier can be configured to format code on file save by using the `.prettierrc` file along with editor-specific configuration.

284. How can you configure ESLint and Prettier to work with an editor or IDE in a React project? 

1. ESLint and Prettier do not have editor or IDE integrations for React projects.
2. ESLint and Prettier automatically integrate with the editor or IDE without any additional configuration.
3. ESLint and Prettier can be integrated with an editor or IDE by installing their respective extensions and configuring the extension settings.
4. ESLint and Prettier can be integrated with an editor or IDE by modifying the global editor configuration file.

285. What is Prettier and how does it differ from ESLint in React development?

1. Prettier is a code formatter that automatically formats code, while ESLint focuses on catching errors and enforcing coding standards.
2. Prettier and ESLint are two different names for the same code formatting tool used in React development.
3. Prettier is a tool for type-checking in React applications, while ESLint is a code formatter.
4. Prettier is a build tool that optimizes React components for production, while ESLint is a linter for catching errors.

286. What is the purpose of the `eslint-plugin-react` plugin in ESLint? 

1. `eslint-plugin-react` is used for enabling React-specific linting rules in ESLint.
2. `eslint-plugin-react` is used for automatically fixing linting issues in React components.
3. `eslint-plugin-react` is used for generating React component documentation from code comments.
4. `eslint-plugin-react` is a deprecated plugin and should not be used in modern React applications.

287. In React, which of the following is a recommended way to handle errors that occur during data fetching?

1. Using try-catch blocks
2. Using error boundaries
3. Ignoring the errors
4. Logging the errors to the console

288. What is a limitation of using React with legacy codebases?

1. React does not have built-in support for integrating with legacy code.
2. React can be difficult to integrate with legacy code.
3. React can cause compatibility issues with older browsers.
4. React can make legacy code more difficult to maintain.

289. Which of the following is NOT a recommended way to handle errors in React?

1. Using error boundaries
2. Using try-catch blocks
3. Ignoring the errors
4. Logging the errors to the console

290. What is ESLint and what is its purpose in React development?

1. ESLint is a tool used for type-checking in React applications.
2. ESLint is a code formatter specifically designed for React code.
3. ESLint is a linter that helps catch and fix code errors and enforce coding standards in React applications.
4. ESLint is a utility for optimizing and bundling React components for production.

291. How can you ignore certain files or directories from being linted by ESLint or formatted by Prettier in a React project? 

1. You cannot exclude files or directories from ESLint or Prettier in a React project.
2. You can exclude files or directories from ESLint by using the `.eslintignore` file and from Prettier by using the `.prettierignore` file.
3. You can exclude files or directories from both ESLint and Prettier by using the `.ignore` file.
4. You can exclude files or directories from ESLint and Prettier by specifying exclusions in the respective configuration files (`.eslintrc` and `.prettierrc`).

292. What is the purpose of the `eslint-plugin-import` plugin in ESLint? 

1. `eslint-plugin-import` is used for enabling linting rules related to import statements in ESLint.
2. `eslint-plugin-import` is used for automatically fixing import-related linting issues in ESLint.
3. `eslint-plugin-import` is used for generating import statement documentation from code comments.
4. `eslint-plugin-import` is a deprecated plugin and should not be used in modern React applications.

293. What is the purpose of React Context in ReactJS? 

1. React Context is used for managing component state in ReactJS.
2. React Context is used for handling routing and navigation in ReactJS.
3. React Context is used for providing global data that can be accessed by multiple components in a ReactJS application.
4. React Context is used for server-side rendering of React components.

294. What is the purpose of React hooks in ReactJS? 

1. React hooks are used for creating custom HTML elements in ReactJS.
2. React hooks are used for managing asynchronous operations in ReactJS.
3. React hooks are used for managing component state and lifecycle in functional components in ReactJS.
4. React hooks are used for handling form validation in ReactJS.

295. What is React Toastify?

1. A JavaScript library for creating pop-up notifications
2. A CSS framework for styling toast messages
3. A server-side rendering solution for React applications
4. A state management library for React

296. How can you install React Toastify in a React project?

1. By including a CDN link in the HTML file
2. By running a command in the terminal
3. By manually downloading and linking the library
4. React Toastify is included by default in React projects

npm install react-toastify

297. How do you display a toast notification using React Toastify?

1. By importing the `ToastContainer` component and rendering it in the component where you want to show the notification
2. By calling the `toast` function and passing the notification message as an argument
3. By adding a custom CSS class to the desired element
4. React Toastify automatically displays toast notifications without any additional code

298. How can you customize the appearance of toast notifications in React Toastify?

1. By passing options as an argument to the `toast` function
2. By applying CSS styles to the `ToastContainer` component
3. By modifying the source code of the React Toastify library
4. React Toastify does not support customization of toast appearance

299. How can you handle user interactions with toast notifications in React Toastify?

1. React Toastify does not support user interactions with toast notifications
2. By adding event listeners to the `ToastContainer` component
3. By providing callbacks through the options argument of the `toast` function
4. By using React's built-in event system and capturing events from the toast elements

300. How can you display a success toast notification with the message "Task completed" using React Toastify?

A.

toast.warning("Task completed");

B.

toast.info("Task completed");

C.

toast.error("Task completed");

D.

toast.success("Task completed");

1. A
2. B
3. C
4. D

import React from 'react';

function UserProfile({ username, bio }) {
 // This component displays a user's profile information.

 // Single-line comment: Here, we receive the username and bio as props.
  return (
    <div classname="user-profile">
      {/* JSX comment: This div holds the user's profile information. */}
      <h2>Welcome, {username}!</h2>
      {
        /*
          Multi-line comment: Inside the div, we display the user's
          username and bio.
        */
      }
      <p>{bio}</p>
    </div>
  );
}

export default UserProfile;

301. What is the purpose of the `toast.success` method in React Toastify?

1. It displays a success toast notification with a green color theme.
2. It removes an existing toast notification from the screen.
3. It opens a new browser tab with additional information about the success.
4. It triggers an error message in the console.

302. How can you add a custom icon to a toast notification in React Toastify?

1. React Toastify does not support custom icons in toast notifications.
2. By using the `icon` property in the `toast` function options.
3. By adding an HTML `img` element inside the toast message content.
4. By modifying the React Toastify source code.

303. How can you configure the position of toast notifications in React Toastify?

1. By setting the `position` property of the `ToastContainer` component
2. By passing options to the `toast` function with the desired position value
3. React Toastify does not provide options for positioning toast notifications
4. By manually adjusting the CSS of the toast notification elements

304. How can you handle multiple toast notifications in React Toastify?

1. By rendering multiple `ToastContainer` components in different parts of your application
2. By using a single `ToastContainer` component and calling the `toast` function multiple times
3. React Toastify does not support displaying multiple toast notifications simultaneously
4. By manually managing an array of toast messages and rendering them conditionally

305. Can you customize the appearance of individual toast notifications in React Toastify?

1. Yes, by passing options as an argument to each `toast` function call
2. No, all toast notifications have the same default appearance
3. By modifying the CSS styles of the `ToastContainer` component
4. React Toastify does not provide customization options for individual toasts

306. Can you programmatically dismiss or remove a toast notification in React Toastify?

1. Yes, by calling the `toast.dismiss` method with the toast ID
2. No, toast notifications are automatically dismissed after a certain duration
3. By triggering a specific event on the `ToastContainer` component
4. React Toastify does not support manual dismissal of toast notifications

307. How can you control the duration of toast notifications in React Toastify?

1. By specifying the `autoClose` option in the `toast` function call
2. By adjusting the default timing settings in the `ToastContainer` component
3. React Toastify does not provide control over the duration of toast notifications
4. By implementing a custom timer using JavaScript's `setTimeout` function