Top 50 React.js Interview MCQs with Answers
Q1. What is React.js primarily used for?
a) Backend development
b) Building user interfaces
c) Database management
d) Server configuration
Answer: b) Building user interfaces
👉 React is a JavaScript library for building fast and interactive UIs.
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Q2. Who developed React.js?
a) Google
b) Microsoft
c) Facebook
d) Amazon
Answer: c) Facebook
👉 React was developed by Facebook in 2013.
Q3. What is JSX in React?
a) JavaScript extension syntax
b) JSON syntax
c) Java syntax extension
d) None of the above
Answer: a) JavaScript extension syntax
👉 JSX allows writing HTML inside JavaScript.
Q4. Which of the following is a feature of React?
a) Virtual DOM
b) One-way data binding
c) Component-based architecture
d) All of the above
Answer: d) All of the above
Q5. Which method is used to create components in React?
a) createComponent()
b) class Component or function
c) makeComponent()
d) renderComponent()
Answer: b) class Component or function
Q6. What is the virtual DOM in React?
a) A browser DOM
b) A lightweight copy of the real DOM
c) An HTML parser
d) A CSS preprocessor
Answer: b) A lightweight copy of the real DOM
Q7. Which command creates a new React app?
a) npx create-react-app app-name
b) npm install react-app app-name
c) react start app-name
d) node create-app app-name
Answer: a) npx create-react-app app-name
Q8. React is mainly focused on which layer of the MVC architecture?
a) Model
b) View
c) Controller
d) Database
Answer: b) View
Q9. What is the default port for running a React app?
a) 3000
b) 8000
c) 5000
d) 8080
Answer: a) 3000
Q10. Which hook is used to manage state in a functional component?
a) useState()
b) useEffect()
c) useReducer()
d) useContext()
Answer: a) useState()
Q11. What does useEffect() hook do in React?
a) Handles routing
b) Manages side effects like API calls
c) Stores state permanently
d) Compiles JSX
Answer: b) Manages side effects like API calls
Q12. How do you pass data from a parent to a child component?
a) Props
b) State
c) Context API
d) Redux
Answer: a) Props
Q13. Which of the following is true about React keys?
a) Keys should always be unique
b) Keys help identify list items
c) Keys improve rendering performance
d) All of the above
Answer: d) All of the above
Q14. What is the correct syntax to write a React fragment?
a)
b) <></>
c) Both a and b
d) None
Answer: c) Both a and b
Q15. What is prop drilling in React?
a) Passing props through multiple nested components
b) Fetching data with props
c) Using props for drilling animations
d) Passing props to the DOM directly
Answer: a) Passing props through multiple nested components
Q16. Which of the following is NOT a React hook?
a) useState
b) useEffect
c) useReducer
d) setState
Answer: d) setState
Q17. What does Redux help with in React?
a) Component rendering
b) State management
c) DOM updates
d) CSS styling
Answer: b) State management
Q18. Which hook replaces lifecycle methods in functional components?
a) useReducer
b) useEffect
c) useState
d) useMemo
Answer: b) useEffect
Q19. Which command is used to install React Router?
a) npm install react-router-dom
b) npm install router
c) npm install react-navigation
d) npm install router-react
Answer: a) npm install react-router-dom
Q20. In React Router, which component is used to define routes?
a) Route
b) Switch
c) BrowserRouter
d) All of the above
Answer: d) All of the above
Q21. What is the purpose of useRef() hook?
a) Manage state
b) Access DOM elements directly
c) Handle routing
d) Fetch data
Answer: b) Access DOM elements directly
Q22. Which hook is used for memoization?
a) useMemo
b) useCallback
c) useRef
d) useState
Answer: a) useMemo
Q23. Which lifecycle method is used in class components for cleanup?
a) componentDidMount
b) componentDidUpdate
c) componentWillUnmount
d) render
Answer: c) componentWillUnmount
Q24. What is the Context API used for?
a) Managing global state
b) Handling routes
c) Managing CSS
d) Building forms
Answer: a) Managing global state
Q25. Which React feature allows components to re-render only when necessary?
a) Virtual DOM
b) PureComponent
c) Memoization
d) All of the above
Answer: d) All of the above
Q26. Which of the following is true about React hooks?
a) Hooks work only inside functional components
b) Hooks must be called at the top level
c) Hooks cannot be conditional
d) All of the above
Answer: d) All of the above
Q27. Which hook is used to optimize functions to prevent unnecessary re-renders?
a) useEffect
b) useCallback
c) useMemo
d) useRef
Answer: b) useCallback
Q28. How do you create a lazy-loaded component in React?
a) React.lazy(() => import('./Component'))
b) React.lazyComponent(‘./Component’)
c) React.load(‘./Component’)
d) React.import(‘./Component’)
Answer: a) React.lazy(() => import('./Component'))
Q29. Which Suspense component is used with lazy loading?
a) Fallback
b) ErrorBoundary
c) CacheBoundary
d) Fragment
Answer: a) Fallback
Q30. Which of the following manages form state in React easily?
a) useState
b) useReducer
c) Formik
d) All of the above
Answer: d) All of the above
Q31. Which of these is a higher-order component (HOC)?
a) A component that renders another component
b) A component that modifies CSS
c) A component that handles routing
d) None of the above
Answer: a) A component that renders another component
Q32. What does React.StrictMode do?
a) Optimizes production build
b) Highlights potential problems in development
c) Improves performance
d) Compiles JSX
Answer: b) Highlights potential problems in development
Q33. Which function is used to update state in a class component?
a) updateState()
b) changeState()
c) setState()
d) modifyState()
Answer: c) setState()
Q34. What does the key prop in React help with?
a) Optimizing list rendering
b) Handling forms
c) CSS animations
d) Debugging
Answer: a) Optimizing list rendering
Q35. Which hook is used to fetch data on component load?
a) useState
b) useEffect
c) useReducer
d) useRef
Answer: b) useEffect
Q36. What is React.memo used for?
a) Memoizing values
b) Preventing unnecessary re-rendering of components
c) Storing data in local storage
d) Handling CSS
Answer: b) Preventing unnecessary re-rendering of components
Q37. Which of the following CSS approaches can be used in React?
a) Inline styles
b) CSS Modules
c) Styled Components
d) All of the above
Answer: d) All of the above
Q38. Which of these is NOT a React state management library?
a) Redux
b) MobX
c) Zustand
d) Django
Answer: d) Django
Q39. Which testing library is most commonly used with React?
a) Jest
b) PyTest
c) Mocha
d) Selenium
Answer: a) Jest
Q40. Enzyme is used for what in React?
a) Styling
b) State management
c) Testing React components
d) Fetching data
Answer: c) Testing React components
Q41. What does ReactDOM.render() do?
a) Renders React elements into the DOM
b) Compiles JSX
c) Updates props
d) Creates routes
Answer: a) Renders React elements into the DOM
Q42. What is reconciliation in React?
a) Comparing old and new virtual DOMs to update only changed parts
b) Updating CSS dynamically
c) Merging props and state
d) Debugging errors
Answer: a) Comparing old and new virtual DOMs to update only changed parts
Q43. Which hook is used to share logic between components?
a) Custom hooks
b) useReducer
c) useContext
d) useEffect
Answer: a) Custom hooks
Q44. Which of these React libraries is used for animations?
a) React Spring
b) Framer Motion
c) React Transition Group
d) All of the above
Answer: d) All of the above
Q45. Which hook can replace Redux for small applications?
a) useContext
b) useMemo
c) useEffect
d) useRef
Answer: a) useContext
Q46. What does React Hydration mean?
a) Rendering React on the server and attaching events on the client
b) Refreshing state automatically
c) Optimizing performance
d) Storing props in memory
Answer: a) Rendering React on the server and attaching events on the client
Q47. What is the default build tool for React apps?
a) Babel
b) Webpack
c) Both (via Create React App)
d) Parcel
Answer: c) Both (via Create React App)
Q48. What is the difference between React Native and React?
a) React Native is for mobile apps, React is for web apps
b) React Native is faster than React
c) React Native uses HTML, React doesn’t
d) React is paid, React Native is free
Answer: a) React Native is for mobile apps, React is for web apps
Q49. Which of the following can trigger a re-render in React?
a) State change
b) Props change
c) Context change
d) All of the above
Answer: d) All of the above
Q50. What is the main advantage of React over traditional JavaScript?
a) Virtual DOM for faster UI updates
b) Component-based architecture
c) Reusable code
d) All of the above
Answer: d) All of the above
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