React JS 100 MCQ. In these 100 Multiple Choice Questions (MCQs), we are going to cover topics such as React basics, JSX, components, Hooks, Redux, performance optimization, and API handling.
React JS 100 MCQ
MCQ Range
Introduction to React
MCQ 1–4
JSX (JavaScript XML)
MCQ 5–7
Components
MCQ 8–12
Events in React
MCQ 13–20
State and Lifecycle
MCQ 21–25
React Hooks
MCQ 26–30
Context API
MCQ 31–34
Forms in React
MCQ 35–40
React Router
MCQ 41–50
Introduction to Redux
MCQ 51–55
Redux with React
MCQ 56–60
Error Boundaries in React
MCQ 61–64
Handling Errors in Async Code
MCQ 65–66
Debugging React Applications
MCQ 67–70
React Performance Techniques
MCQ 71–80
Fetching Data
MCQ 81–85
RESTful APIs
MCQ 86–90
Unit Testing React Components
MCQ 91–95
Styling Components in React
MCQ 96–100
Question 1: What is React primarily used for?
A. To manage databases
B. To create dynamic user interfaces
C. To optimize server performance
D. To handle large datasets efficiently
B. React is primarily used to create dynamic and interactive user interfaces.
Question 2: How is React different from other JavaScript frameworks like Angular and Vue?
A. React uses a real DOM
B. React uses a virtual DOM
C. React operates on a backend server
D. React doesn’t support component-based architecture
B. React uses a virtual DOM to enhance performance compared to the real DOM.
Question 3: What does the virtual DOM in React do?
A. It updates synchronously with the real DOM
B. It is a lightweight copy of the real DOM and updates asynchronously
C. It mirrors the real DOM in real-time
D. It is only used for server-side rendering
B. The virtual DOM is a lightweight version of the real DOM that updates asynchronously.
Question 4: Which of the following best describes JSX?
A. A JavaScript library
B. A syntax extension for writing HTML within JavaScript
C. A method for handling events
D. A way to style React components
B. JSX is a syntax extension that allows developers to write HTML within JavaScript.
Question 5: What does JSX stand for?
A. JavaScript Extra
B. JavaScript XML
C. JavaScript Execution
D. JavaScript Extension
B. JSX stands for JavaScript XML and is a syntax extension for writing HTML-like code inside JavaScript.
Question 6: How can you embed JavaScript expressions in JSX?
A. Using square brackets [ ]
B. Using double curly braces {{ }}
C. Using parentheses ( )
D. Using single curly braces { }
D. JavaScript expressions in JSX are embedded using single curly braces { }.
Question 7: Which of the following is an advantage of using JSX?
A. It allows for more efficient DOM manipulation
B. It provides better performance than JavaScript
C. It allows writing HTML elements directly inside JavaScript
D. It removes the need for JavaScript entirely
C. JSX allows developers to write HTML elements directly inside JavaScript.
Question 8: What is a functional component in React?
A. A class that returns HTML elements
B. A function that returns HTML elements using JSX
C. A method used to handle events
D. A class that manages state
B. A functional component is a JavaScript function that returns HTML elements using JSX.
Question 9: What is the primary difference between functional and class components in React?
A. Functional components can handle state
B. Class components can use lifecycle methods
C. Functional components can directly manipulate the DOM
D. Class components are stateless
B. Class components can use lifecycle methods like componentDidMount, while functional components cannot unless using Hooks.
Question 10: What are props in React used for?
A. To manage component lifecycle
B. To handle events in a component
C. To pass data between components
D. To manipulate the DOM
C. Props are used to pass data from one component to another in React.
Question 11: Which method is required in a React class component?
A. render
B. componentDidMount
C. constructor
D. getDerivedStateFromProps
A. The render method is required in a React class component as it returns the HTML for the component.
Question 12: What is the main purpose of state in a React component?
A. To pass data to child components
B. To manage dynamic data within a component
C. To define static properties
D. To handle user inputs
B. State in React is used to manage dynamic data that affects how a component renders.
Question 13: How does React handle events?
A. React uses the browser’s native event system
B. React uses its own synthetic event system
C. React handles events asynchronously
D. React does not support events
B. React uses a synthetic event system that wraps around the browser’s native event system, providing cross-browser compatibility.
Question 14: Which of the following is an example of event binding in React?
A. onClick={this.handleClick.bind(this)}
B. onClick={this.handleClick()}
C. onClick=”this.handleClick()”
D. onclick={this.handleClick}
A. Event binding in React class components can be done by using onClick={this.handleClick.bind(this)} to bind the method’s ‘this’ context.
Question 15: How can you prevent the default behavior of an event in React?
A. Using stopPropagation()
B. Using event.preventDefault()
C. Using return false
D. Using a callback function
B. You can prevent the default behavior of an event in React by calling event.preventDefault() inside the event handler.
Question 16: What is event delegation in React?
A. Handling multiple events in one component
B. Handling events on the parent component instead of individual child elements
C. Using events to manipulate state
D. Using event listeners directly on child components
B. Event delegation in React refers to handling events on the parent component rather than individual child elements.
Question 17: Which of the following is the correct way to handle an event in React?
A. onClick=”handleClick()”
B. onClick={this.handleClick()}
C. onClick=”this.handleClick.bind(this)”
D. onClick={this.handleClick}
D. The correct syntax for handling events in React is onClick={this.handleClick}.
Question 18: How does React handle form inputs using events like onChange?
A. By using native browser events
B. By using a synthetic event system
C. By automatically updating the state
D. By binding the input value to the DOM
B. React handles form inputs using its synthetic event system.
Question 19: Which of the following is a correct example of using the onChange event in React?
A. <input onChange=”handleChange()” />
B. <input onChange={this.handleChange()} />
C. <input onChange={this.handleChange} />
D. <input onChange=”this.handleChange” />
C. The correct syntax for using the onChange event in React is onChange={this.handleChange}.
Question 20: How can you bind an event handler to ensure it has the correct ‘this’ context in class components?
A. By using this.methodName.bind(this) in the constructor
B. By using arrow functions inside the render method
C. By assigning the method to a variable
D. By using setState inside the method
A. You can bind an event handler to the correct ‘this’ context in React class components using this.methodName.bind(this) in the constructor.
Question 21: What is the purpose of the state in React?
A. To store dynamic data that affects how the component renders
B. To pass data between components
C. To trigger events in the DOM
D. To define static variables for a component
A. State in React is used to store dynamic data that can change over time and affect the rendering of the component.
Question 22: Which lifecycle method is called when a component is first rendered to the DOM?
A. componentDidMount
B. componentDidUpdate
C. componentWillUnmount
D. shouldComponentUpdate
A. The componentDidMount lifecycle method is called once after the component is rendered to the DOM.
Question 23: How do functional components manage state in React?
A. By using the useState hook
B. By using the this.state object
C. By directly modifying the DOM
D. By calling lifecycle methods
A. Functional components use the useState hook to manage state in React.
Question 24: What is the role of the componentWillUnmount lifecycle method?
A. To initialize state
B. To clean up resources before the component is unmounted
C. To handle side effects after rendering
D. To update the component state
B. componentWillUnmount is used to clean up resources like subscriptions or event listeners before the component is removed from the DOM.
Question 25: What is the correct syntax for updating state in a React class component?
A. this.state = { value: newValue }
B. this.setState({ value: newValue })
C. state = { value: newValue }
D. setState({ value: newValue })
B. In a class component, you update state using this.setState({ value: newValue }).
Question 26: What is the useState hook used for in React?
A. To manage side effects in a functional component
B. To set and update the state in functional components
C. To handle lifecycle methods in class components
D. To manage props between components
B. The useState hook is used to initialize and update state in functional components.
Question 27: What does the useEffect hook allow you to do?
A. Handle side effects like data fetching or subscriptions
B. Manage local component state
C. Pass data to child components
D. Access the component lifecycle methods in class components
A. The useEffect hook allows you to handle side effects like data fetching, subscriptions, and timers.
Question 28: Which of the following is a correct example of using the useState hook?
A. const [value, setValue] = setState(0);
B. const [value, setValue] = useState(0);
C. const [value, setValue] = state(0);
D. const [value, setValue] = updateState(0);
B. The correct syntax for using the useState hook is const {value, setValue} = useState(0);
Question 29: What does the useContext hook allow you to do?
A. Access the global state across all components
B. Consume context values without prop drilling
C. Directly update the parent component’s state
D. Set initial state for functional components
B. The useContext hook allows you to consume context values without passing them through every level of a component tree (prop drilling).
Question 30: How does the useReducer hook differ from the useState hook?
A. useReducer is used for handling complex state logic, while useState is for simple state management
B. useReducer can only be used in class components
C. useReducer is for managing side effects
D. useState is asynchronous, but useReducer is synchronous
A. The useReducer hook is used for managing more complex state logic than the useState hook.
Question 31: What is the main purpose of the Context API in React?
A. To optimize component performance
B. To share global data across multiple components without prop drilling
C. To handle event propagation
D. To manage lifecycle methods
B. The Context API allows you to share global data across multiple components without needing to pass props down through every level.
Question 32: How do you create a Context in React?
A. By using useState
B. By using React.createContext()
C. By using the useEffect hook
D. By defining a new component
B. You create a context in React using React.createContext().
Question 33: What is the main difference between Context API and Redux?
A. Context API is for managing global state, Redux is for styling components
B. Context API is built-in to React, while Redux is an external library
C. Redux uses the virtual DOM, while Context API doesn’t
D. Redux is synchronous, while Context API is asynchronous
B. Context API is built-in to React, while Redux is an external library used for complex state management.
Question 34: How do you consume values from a Context in functional components?
A. By using the useEffect hook
B. By using the useContext hook
C. By using the useState hook
D. By directly accessing the context object
B. You consume values from a Context in functional components using the useContext hook.
Question 35: What is a controlled component in React?
A. A component that manages its own state
B. A component where form data is handled by the DOM
C. A component where form data is controlled by React through state
D. A component that updates asynchronously
C. A controlled component is one where form data is managed by React using state, rather than the DOM.
Question 36: How do you handle form submission in React?
A. By using the submit event of the form
B. By manually updating the state
C. By preventing the default form behavior using event.preventDefault()
D. By using a synthetic event handler
C. You handle form submission in React by using event.preventDefault() to prevent the default browser form submission behavior.
Question 37: What is the key difference between controlled and uncontrolled components in React?
A. Controlled components are more performant
B. Uncontrolled components manage form data through the DOM, while controlled components manage it through React state
C. Controlled components do not need state
D. Uncontrolled components can directly modify props
B. Uncontrolled components manage form data through the DOM, while controlled components manage it through React state.
Question 38: Which of the following is an example of a controlled component?
A. <input defaultValue=”text” />
B. <input value={this.state.value} onChange={this.handleChange} />
C. <input type=”submit” />
D. <input ref={inputRef} />
B. A controlled component is one where the input’s value is managed by React state, using value and onChange attributes.
Question 39: How do you handle validation in forms in React?
A. By writing validation logic inside the onSubmit handler
B. By using the componentWillUpdate lifecycle method
C. By attaching validation to the form tag
D. By using context to pass validation rules
A. Validation in forms is typically handled by writing logic inside the onSubmit handler to validate the form inputs before submission.
Question 40: Which of the following is an advantage of using controlled components in forms?
A. They allow for direct DOM manipulation
B. They make it easier to handle form validation and control user input
C. They reduce the need for event handling
D. They eliminate the need for state
B. Controlled components make it easier to handle form validation and control user input, as the form data is managed by React state.
Question 41: What is React Router used for in a React application?
A. To manage component state
B. To handle navigation and routing between different components
C. To optimize performance
D. To fetch data from APIs
B. React Router is used to handle navigation and routing between different components in a React application.
Question 42: How do you set up routing in a React application?
A. By importing and using the BrowserRouter, Route, and Switch components
B. By using a state variable to track routes
C. By writing custom functions to handle navigation
D. By embedding links inside components
A. You set up routing in React by using the BrowserRouter, Route, and Switch components from React Router.
Question 43: What is the purpose of the Switch component in React Router?
A. To load the styles for the active route
B. To group multiple routes and render only the first matching route
C. To manage global state between components
D. To switch between different components based on user inputs
B. The Switch component renders the first child Route that matches the current location, ensuring that only one route is rendered at a time.
Question 44: What is a common use case for route parameters in React Router?
A. To pass dynamic values through the URL
B. To store user data in local storage
C. To track user session information
D. To update the component state
A. Route parameters allow you to pass dynamic values through the URL, which can be used to render specific data for a particular route.
Question 45: How do you define a route with a parameter in React Router?
A. <Route path=”/user/:id” component={UserComponent} />
B. <Route path=”/user?id” component={UserComponent} />
C. <Route param=”/user/:id” component={UserComponent} />
D. <Route query=”/user?id” component={UserComponent} />
A. A route with a parameter in React Router is defined using a colon before the parameter name, such as path=”/user/”.
Question 46: How do you access route parameters in a component?
A. Through the props object using props.match.params
B. By reading from local storage
C. By using the useState hook
D. Through the state object using state.params
A. Route parameters in React Router can be accessed through the props object using props.match.params.
Question 47: What is the purpose of the Link component in React Router?
A. To handle API requests
B. To create navigation links that update the URL without refreshing the page
C. To render a new component
D. To store data in session storage
B. The Link component in React Router is used to create navigation links that allow users to navigate between routes without reloading the page.
Question 48: How can you redirect users programmatically in React Router?
A. By modifying the URL directly
B. By using the history object in combination with history.push()
C. By setting a new state value
D. By using the onClick event
B. You can redirect users programmatically in React Router by using the history object and calling history.push().
Question 49: What is the purpose of the useHistory hook in React Router?
A. To manage state transitions
B. To give access to the history object for navigation purposes
C. To access route parameters
D. To handle form submissions
B. The useHistory hook gives access to the history object, which can be used for programmatic navigation within a React component.
Question 50: How can you handle nested routes in React Router?
A. By using a single Route component
B. By placing child Route components inside a parent Route component
C. By defining routes in the state
D. By using the Link component inside each route
B. Nested routes are handled by placing child Route components inside a parent Route component, allowing for more complex navigation structures.
Question 51: What is the main purpose of Redux in a React application?
A. To handle routing
B. To manage global state across the entire application
C. To handle form submissions
D. To manage local component styles
B. Redux is used to manage global state across the entire React application, making state accessible from any component.
Question 52: Which of the following is a core concept of Redux?
A. Props and Context
B. State and Effects
C. Actions, Reducers, and Store
D. Components and Hooks
C. The core concepts of Redux are Actions, Reducers, and Store.
Question 53: What is an action in Redux?
A. A function that modifies the state directly
B. A plain JavaScript object that describes an event or change in state
C. A function that fetches data from an API
D. A method for rendering components
B. An action in Redux is a plain JavaScript object that describes a change or event in the application state.
Question 54: What is the purpose of a reducer in Redux?
A. To fetch data from APIs
B. To update the component tree
C. To specify how the application’s state changes in response to an action
D. To dispatch actions to components
C. A reducer specifies how the application’s state changes in response to an action in Redux.
Question 55: How is the Redux store created in a React application?
A. By calling createStore and passing in the root reducer
B. By using useState
C. By importing the store from the component file
D. By setting state manually in the constructor
A. The Redux store is created by calling createStore and passing in the root reducer.
Question 56: How do you connect a React component to the Redux store?
A. By using the useState hook
B. By using the connect function from react-redux
C. By importing the store directly into the component
D. By using the setState function
B. React components are connected to the Redux store by using the connect function from react-redux.
Question 57: What does the mapStateToProps function do in Redux?
A. It dispatches actions to the store
B. It maps the state from the Redux store to the props of the component
C. It initializes the component’s state
D. It handles API calls in Redux
B. The mapStateToProps function maps the state from the Redux store to the props of the connected component.
Question 58: What is the purpose of the mapDispatchToProps function in Redux?
A. To map component state to the store
B. To map action dispatchers to the component props
C. To handle side effects
D. To update the Redux store automatically
B. The mapDispatchToProps function maps dispatchable actions to the props of the component.
Question 59: Which of the following is a common use case for Redux middleware?
A. To manage component state
B. To handle asynchronous actions like API calls
C. To handle form validation
D. To manage routing in the application
B. Redux middleware is commonly used to handle asynchronous actions such as API calls in the application.
Question 60: What does Redux Thunk allow you to do?
A. Write action creators that return functions instead of action objects
B. Manage routing in a React application
C. Render components conditionally
D. Fetch data from APIs synchronously
A. Redux Thunk allows action creators to return functions instead of plain action objects, enabling asynchronous actions like API calls.
Question 61: What are error boundaries in React used for?
A. To catch JavaScript errors in the entire application
B. To catch errors in a component’s child tree during rendering
C. To prevent re-rendering of a component
D. To handle routing errors
B. Error boundaries are React components that catch JavaScript errors in their child component tree during rendering, preventing the application from crashing.
Question 62: Which lifecycle method is used to catch errors in an error boundary?
A. componentDidCatch
B. componentDidMount
C. componentWillUnmount
D. componentWillUpdate
A. The componentDidCatch lifecycle method is used in error boundaries to catch errors that occur in the component tree.
Question 63: Can error boundaries catch errors in event handlers?
A. Yes, error boundaries catch all types of errors
B. No, error boundaries do not catch errors in event handlers
C. Only if the error handler is asynchronous
D. Only when combined with Redux
B. Error boundaries do not catch errors in event handlers, which need to be handled with try-catch blocks inside the event handler.
Question 64: What happens if an error boundary catches an error?
A. It silently logs the error and continues rendering
B. It displays a fallback UI instead of crashing the application
C. It automatically fixes the error
D. It stops the component from rendering and shows a warning
B. When an error boundary catches an error, it displays a fallback UI, preventing the entire application from crashing.
Question 65: What is the best way to handle errors in async code in React?
A. By using error boundaries
B. By wrapping async code in a try-catch block
C. By using componentWillUnmount
D. By preventing state updates
B. Async code errors in React should be handled by wrapping the code in a try-catch block.
Question 66: How can you handle errors in Promises in React?
A. By adding error handling in componentDidMount
B. By using .catch() at the end of the Promise chain
C. By using preventDefault in the Promise
D. By updating the state with the error message
B. Errors in Promises can be handled by adding a .catch() block at the end of the Promise chain.
Question 67: Which of the following tools is most commonly used for debugging React applications?
A. Chrome DevTools
B. Node.js
C. React Developer Tools
D. Redux DevTools
C. React Developer Tools is a browser extension used specifically for inspecting and debugging React applications.
Question 68: How can you inspect the state and props of a React component during development?
A. By using the console.log method
B. By using the React Developer Tools
C. By directly accessing the component’s state in the DOM
D. By using componentDidCatch
B. You can inspect the state and props of a React component using React Developer Tools, which shows the component tree and the current values of props and state.
Question 69: What does the profiler feature in React Developer Tools do?
A. It allows you to directly modify state values
B. It helps identify performance bottlenecks by recording renders and updates
C. It displays errors in your component tree
D. It tracks state changes in Redux
B. The profiler feature in React Developer Tools helps identify performance bottlenecks by recording renders and updates of components.
Question 70: How can you view performance optimizations or re-renders in React?
A. By using the console.log method
B. By using the performance tab in React Developer Tools
C. By using setState
D. By using the Network tab in Chrome DevTools
B. You can view performance optimizations or re-renders in React using the performance tab in React Developer Tools, which shows how components are being rendered.
Question 71: What is the purpose of memoization in React?
A. To increase the size of the DOM
B. To prevent unnecessary re-renders by caching the results of function calls
C. To automatically handle API requests
D. To simplify the component lifecycle
B. Memoization in React is used to prevent unnecessary re-renders by caching the results of function calls and reusing them when the inputs haven’t changed.
Question 72: Which hook in React can be used to memoize values?
A. useEffect
B. useState
C. useMemo
D. useContext
C. The useMemo hook is used to memoize values, ensuring that expensive calculations are only performed when necessary.
Question 73: What is the purpose of the useCallback hook?
A. To memoize function definitions and prevent them from being recreated on every render
B. To trigger a component re-render
C. To handle side effects in functional components
D. To update the state in class components
A. The useCallback hook memoizes function definitions so that they are not recreated on every render, which can improve performance.
Question 74: How can React.memo help optimize component performance?
A. By preventing a component from re-rendering unless its props change
B. By preventing the component tree from updating
C. By automatically handling state updates
D. By preventing side effects in functional components
A. React.memo is a higher-order component that prevents a component from re-rendering unless its props have changed, optimizing performance.
Question 75: What is the purpose of code splitting in React?
A. To load all JavaScript files at once
B. To load only the necessary JavaScript files when needed, improving load times
C. To merge CSS and JavaScript files
D. To prevent re-renders
B. Code splitting is a performance optimization technique that allows React to load only the necessary JavaScript files when needed, improving load times.
Question 76: Which of the following methods can be used for lazy loading components in React?
A. useState
B. useEffect
C. React.lazy
D. React.memo
C. React.lazy is used to lazy load components in React, meaning they are only loaded when needed.
Question 77: How does the useMemo hook improve performance in React?
A. By memoizing values and preventing expensive recalculations on each render
B. By preventing component re-renders
C. By fetching data automatically
D. By handling lifecycle methods in functional components
A. The useMemo hook memoizes values, ensuring that expensive recalculations are only performed when necessary, improving performance.
Question 78: What is the purpose of the shouldComponentUpdate lifecycle method in class components?
A. To force a component to always update
B. To allow React to decide whether to re-render a component based on changes to props or state
C. To prevent state updates in a component
D. To handle form submissions
B. shouldComponentUpdate allows React to decide whether to re-render a component based on changes to its props or state, which can improve performance by avoiding unnecessary renders.
Question 79: What is the role of the React Profiler?
A. To track and visualize the performance of components in terms of rendering time
B. To store component data
C. To automatically fix performance issues
D. To handle error boundaries
A. The React Profiler tracks and visualizes the performance of components, helping developers understand rendering times and identify performance bottlenecks.
Question 80: Which of the following is a way to fix memory leaks in React applications?
A. By clearing intervals and timeouts in the componentWillUnmount lifecycle method
B. By updating the state on each render
C. By using inline styles instead of CSS
D. By preventing the component from rendering
A. Memory leaks can be fixed by clearing intervals and timeouts in the componentWillUnmount lifecycle method to ensure resources are properly cleaned up when a component is unmounted.
Question 81: Which method is commonly used in React to fetch data from an API?
A. useState
B. fetch or Axios
C. useEffect
D. React.memo
B. The fetch method and Axios are commonly used in React to fetch data from APIs.
Question 82: Where is the best place to fetch data in a React component?
A. Inside the render method
B. Inside a useEffect hook
C. Inside the constructor
D. Inside the event handler
B. Data fetching is typically done inside a useEffect hook in functional components to ensure it happens after the component mounts.
Question 83: How can you handle asynchronous data fetching in React?
A. By using synchronous functions only
B. By using Promises or async/await inside useEffect
C. By directly manipulating the DOM
D. By using the useState hook alone
B. Asynchronous data fetching in React is commonly handled using Promises or async/await inside the useEffect hook.
Question 84: What is the purpose of handling loading states when fetching data in React?
A. To prevent re-rendering
B. To display a loading indicator while waiting for the data
C. To automatically update the state
D. To cache the API response
B. Handling loading states allows you to display a loading indicator while data is being fetched, improving the user experience.
Question 85: How do you handle errors when fetching data from an API in React?
A. By using try-catch blocks in async/await functions or .catch() in Promises
B. By ignoring the API call if it fails
C. By automatically retrying the API call
D. By wrapping the component with an error boundary
A. Errors during data fetching are handled using try-catch blocks in async/await functions or .catch() in Promises.
Question 86: Which HTTP methods are commonly used for CRUD operations in RESTful APIs?
A. GET, POST, PUT, DELETE
B. HEAD, PATCH, TRACE, OPTIONS
C. CONNECT, UPDATE, DELETE, FETCH
D. POST, GET, PATCH, UPDATE
A. The common HTTP methods for CRUD operations in RESTful APIs are GET, POST, PUT, and DELETE.
Question 87: How can you perform a GET request in React using Axios?
A. axios.get(‘/url’)
B. fetch(‘/url’)
C. useEffect()
D. axios.post(‘/url’)
A. A GET request can be performed using Axios with the axios.get(‘/url’) method.
Question 88: What is the purpose of using async/await in API calls in React?
A. To handle synchronous operations
B. To make asynchronous code easier to write and read
C. To replace Promises entirely
D. To handle form validation
B. Async/await makes asynchronous code easier to write and read by allowing the use of synchronous-looking syntax for asynchronous operations.
Question 89: What is the main advantage of using Axios over the fetch API in React?
A. Axios is synchronous by default
B. Axios automatically handles JSON responses and has a more user-friendly API
C. Axios only supports POST requests
D. Axios is a built-in feature of React
B. Axios provides automatic JSON handling, simplified syntax, and additional features like request/response interceptors, making it more user-friendly than fetch.
Question 90: How do you perform a POST request in React using the fetch API?
A. fetch(‘/url’, { method: ‘POST’, body: JSON.stringify(data) })
B. axios.post(‘/url’, data)
C. fetch(‘/url’)
D. axios.get(‘/url’, data)
A. A POST request using the fetch API is done with fetch(‘/url’, { method: ‘POST’, body: JSON.stringify(data) }).
Question 91: What is the purpose of unit testing in React?
A. To test the entire application as a whole
B. To test individual components in isolation
C. To test the performance of React applications
D. To handle asynchronous operations
B. Unit testing in React involves testing individual components in isolation to ensure they work as expected.
Question 92: Which library is commonly used for testing React components?
A. Axios
B. Redux
C. Jest and React Testing Library
D. Mocha
C. Jest and React Testing Library are commonly used for testing React components.
Question 93: What is snapshot testing in React?
A. A type of testing that compares a rendered component’s output to a previously stored snapshot
B. A testing method that tracks state changes
C. A method of testing API requests
D. A tool for monitoring performance
A. Snapshot testing compares the rendered output of a component to a previously stored snapshot to detect unexpected changes.
Question 94: How can you mock API calls in unit tests for React components?
A. By making real API requests
B. By using Jest or other testing libraries to simulate API responses
C. By testing the API directly in the component
D. By calling the API in the constructor
B. Mocking API calls in unit tests is typically done using Jest or other testing libraries to simulate API responses.
Question 95: What is the primary advantage of using Jest for testing React applications?
A. Jest is faster than other testing tools
B. Jest has built-in support for mocking, snapshot testing, and easy configuration for React apps
C. Jest automatically generates tests for components
D. Jest is a feature of React itself
B. Jest provides built-in support for mocking, snapshot testing, and easy configuration for React applications, making it a popular choice for testing React components.
Question 96: What is CSS-in-JS in React?
A. A way to write JavaScript inside CSS files
B. A method for writing styles within JavaScript files using libraries like styled-components or Emotion
C. A way to include external CSS files in JavaScript
D. A feature that eliminates the need for styling in React
B. CSS-in-JS refers to writing styles directly in JavaScript files using libraries like styled-components or Emotion.
Question 97: Which of the following is a benefit of using CSS-in-JS in React?
A. It makes styles global across the application
B. It allows for scoped styles within components
C. It eliminates the need for state management
D. It only works in class components
B. CSS-in-JS allows for scoped styles within components, which helps avoid class name collisions.
Question 98: What is the difference between inline styles and external stylesheets in React?
A. Inline styles are written directly in the component’s JSX, while external stylesheets are stored separately and linked to the component
B. Inline styles perform better than external stylesheets
C. External stylesheets cannot be used in React components
D. Inline styles are only for functional components
A. Inline styles are written directly within the component’s JSX, while external stylesheets are stored in separate files and linked to the component.
Question 99: What are CSS modules in React?
A. A way to include JavaScript logic inside CSS files
B. A method for writing locally scoped CSS classes
C. A replacement for inline styles
D. A method for combining multiple CSS files into one
B. CSS modules allow developers to write locally scoped CSS classes that only apply to the component where they are used.
Question 100: Which of the following is a best practice when styling components in React?
A. Use inline styles for all components
B. Use globally scoped styles for better control
C. Use scoped or modular styles to prevent style conflicts across components
D. Avoid using external stylesheets
C. It is a best practice to use scoped or modular styles to prevent style conflicts across components and ensure maintainability.
