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Section 1 — Core JavaScript

Questions 1–10

10 Qs

01What are the differences between var, let, and const? Explain scope, hoisting, and re-assignment rules.Basic

02What is a closure in JavaScript? Provide a real-world example where closures are useful.Medium

03Explain the concept of the JavaScript event loop, call stack, and the difference between the microtask queue and macrotask queue.Advanced

04What is this in JavaScript? Explain how its value changes in regular functions, arrow functions, methods, and event handlers.Medium

05What is prototypal inheritance in JavaScript? How does the prototype chain work?Medium

06What is the difference between == and ===? Explain type coercion with examples.Basic

07What is hoisting in JavaScript? How does it affect var declarations and function declarations differently?Basic

08What is the difference between null and undefined? When would each be used?Basic

09Explain call(), apply(), and bind() methods. What is the difference between them?Medium

10What is a pure function? Why is immutability important in JavaScript and React?Medium

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Section 2 — ES6+ Modern Features

Questions 11–20

10 Qs

11What are arrow functions? How do they differ from regular functions in terms of syntax and this binding?Basic

12Explain destructuring assignment for both arrays and objects. What are the use-cases?Basic

13What are template literals? How do tagged template literals work?Basic

14Explain the spread operator ... and rest parameters. How are they different?Basic

15What are ES6 Modules (import/export)? How do named exports differ from default exports?Basic

16What are Map and Set in JavaScript? How do they differ from plain objects and arrays?Medium

17What are JavaScript Symbols? What are they used for and give an example of a well-known Symbol.Advanced

18What are Generators in JavaScript? Explain function* and yield with a practical example.Advanced

19What is optional chaining (?.) and nullish coalescing (??)? How do they simplify code?Medium

20What are WeakMap and WeakSet? How do they differ from Map and Set and when would you use them?Advanced

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Section 3 — Async JavaScript & Promises

Questions 21–30

10 Qs

21What is a JavaScript Promise? Explain the three states: pending, fulfilled, and rejected.Basic

22What is the difference between Promise.all(), Promise.race(), Promise.allSettled(), and Promise.any()?Medium

23What is async/await? How does it simplify working with Promises and how do you handle errors?Basic

24What are callbacks? What is callback hell and how do Promises or async/await solve it?Basic

25Explain the difference between setTimeout, setInterval, and requestAnimationFrame.Medium

26What is the Fetch API? How does it differ from XMLHttpRequest? Write an example with error handling.Basic

27What is debouncing and throttling? Implement both from scratch and describe their use-cases.Medium

28What are Web Workers? How do they enable true parallelism in JavaScript?Advanced

29What is the difference between synchronous and asynchronous iteration? Explain for await...of.Advanced

30What is an AbortController? How do you cancel a fetch request in JavaScript?Medium

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Section 4 — React Fundamentals

Questions 31–40

10 Qs

31What is React and what problems does it solve? What is the Virtual DOM and how does it work?Basic

32What is JSX? How is it different from HTML and how is it transformed under the hood?Basic

33What is the difference between class components and functional components? Why are functional components preferred?Basic

34What are props in React? How do you pass data from a parent to a child component? What are prop types?Basic

35What is state in React? How is it different from props and when should you use each?Basic

36What is the React component lifecycle? Describe the main phases (mounting, updating, unmounting) for class components.Medium

37What is reconciliation in React? Explain the diffing algorithm and what the key prop is used for.Medium

38What are controlled vs uncontrolled components in React? Give examples of each.Medium

39What are React Fragments? Why would you use <>...</> instead of a wrapper <div>?Basic

40What are Error Boundaries in React? How do you implement one and what errors do they catch?Medium

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Section 5 — React Hooks

Questions 41–50

10 Qs

41What is useState? Explain its syntax, how state updates are batched, and the functional updater pattern.Basic

42What is useEffect? Explain the dependency array — what happens with no array, an empty array, and values in the array?Basic

43What is useContext? How does it help avoid prop drilling? What are its limitations?Medium

44What is useReducer? When would you use it over useState? Implement a simple counter with it.Medium

45What is useMemo? Explain when to use it and what the performance trade-offs are.Medium

46What is useCallback? How does it differ from useMemo? When is it necessary?Medium

47What is useRef? Explain its two main use-cases: accessing DOM elements and persisting mutable values.Medium

48What are custom hooks? Write a custom useFetch hook that handles loading and error states.Medium

49What is useLayoutEffect? How does it differ from useEffect and when should you use it?Advanced

50What are the Rules of Hooks? Why can't hooks be called inside conditions or loops?Basic

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Section 6 — State Management

Questions 51–60

10 Qs

51What is the Context API in React? How does it work and what are its performance considerations?Medium

52What is Redux? Explain its three core principles, and the roles of actions, reducers, and the store.Medium

53What is Redux Toolkit (RTK)? How does createSlice and configureStore simplify Redux usage?Medium

54What is Redux middleware? Explain Redux Thunk vs Redux Saga — what are the trade-offs?Advanced

55What is Zustand? How does it compare to Redux for managing global state?Medium

56What is React Query (TanStack Query)? How does it handle server state differently from client state tools?Advanced

57What is prop drilling and how can you solve it? Compare Context API, Redux, Zustand, and component composition.Medium

58What is the difference between local state, global state, and server state? Give examples of each.Basic

59What is Recoil or Jotai? How do atom-based state managers differ from flux-based ones like Redux?Advanced

60How do you persist state across page refreshes in React? Compare localStorage, sessionStorage, and cookies.Medium

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Section 7 — Advanced React Patterns

Questions 61–70

10 Qs

61What are Higher-Order Components (HOCs)? Write an example and explain when to use them vs hooks.Advanced

62What is the Render Props pattern? How does it compare to HOCs and custom hooks?Advanced

63What is the Compound Component pattern? Give a real-world example (e.g., a custom <Tabs> component).Advanced

64What is React.memo? How does it prevent unnecessary re-renders and when should you NOT use it?Medium

65What are Portals in React? When would you use ReactDOM.createPortal()? Give a practical example.Medium

66What is React Suspense? How does it work with lazy loading and data fetching?Advanced

67What is React.lazy() and code splitting? How does it work with dynamic import()?Medium

68What is the Forwarding Refs pattern? Explain React.forwardRef() and when it is needed.Advanced

69What is React Concurrent Mode and the useTransition hook? How does it improve UX?Advanced

70What is Server-Side Rendering (SSR) in React? How does it differ from Client-Side Rendering (CSR) and Static Site Generation (SSG)?Advanced

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Section 8 — Performance Optimization

Questions 71–80

10 Qs

71What causes unnecessary re-renders in React? List five common causes and how to fix each.Medium

72What is memoization? Explain how useMemo, useCallback, and React.memo work together.Medium

73What is virtualization / windowing in React? When and how would you use react-window or react-virtual?Advanced

74What are Core Web Vitals (LCP, FID/INP, CLS)? How do you improve them in a React app?Advanced

75How does bundle splitting and tree shaking work? What tools (Webpack, Vite) help optimize bundle size?Advanced

76What is lazy loading of images and routes? How do you implement it in a React app?Medium

77What are service workers and caching strategies? How do they help with React app performance?Advanced

78How do you use the React DevTools Profiler to identify performance bottlenecks?Medium

79What is event delegation? How does it improve performance with large lists in the DOM?Medium

80What is the difference between innerHTML and textContent? What are the security implications of using innerHTML?Medium

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Section 9 — Routing & API Integration

Questions 81–88

8 Qs

81What is React Router? Explain the difference between BrowserRouter, HashRouter, and MemoryRouter.Basic

82What is the difference between useNavigate, useParams, and useLocation hooks in React Router v6?Medium

83How do you implement protected routes (auth guards) in React Router?Medium

84What is REST vs GraphQL? When would you choose GraphQL over REST in a React application?Medium

85What is Axios? How does it differ from the Fetch API and what additional features does it provide?Basic

86How do you handle API errors gracefully in React? Explain loading, error, and success states with a pattern.Medium

87What are WebSockets? How do you implement real-time data in React using WebSockets or Server-Sent Events?Advanced

88What is CORS? How does it affect API calls from a React app and how is it configured on the server?Medium

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Section 10 — Testing React Applications

Questions 89–95

7 Qs

89What is the difference between unit, integration, and end-to-end (E2E) testing? Give examples for a React app.Basic

90What is Jest? What are describe, it/test, expect, and matchers? Write a simple unit test.Basic

91What is React Testing Library (RTL)? What is its philosophy and how does getByRole, getByText, and userEvent work?Medium

92What are mocks and spies in Jest? How do you mock a module, API call, or React hook?Medium

93How do you test custom React hooks? What is renderHook from React Testing Library?Medium

94What is Cypress or Playwright? How does E2E testing differ from component testing and when is each appropriate?Advanced

95What is snapshot testing in Jest? What are its benefits and pitfalls?Medium

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React & JavaScript
Question Set

10 Key React & JS Areas

All 95+ Questions

Section 1 — Core JavaScript

Section 2 — ES6+ Modern Features

Section 3 — Async JavaScript & Promises

Section 4 — React Fundamentals

Section 5 — React Hooks

Section 6 — State Management

Section 7 — Advanced React Patterns

Section 8 — Performance Optimization

Section 9 — Routing & API Integration

Section 10 — Testing React Applications

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React & JavaScript Question Set

10 Key React & JS Areas

All 95+ Questions

Section 1 — Core JavaScript

Section 2 — ES6+ Modern Features

Section 3 — Async JavaScript & Promises

Section 4 — React Fundamentals

Section 5 — React Hooks

Section 6 — State Management

Section 7 — Advanced React Patterns

Section 8 — Performance Optimization

Section 9 — Routing & API Integration

Section 10 — Testing React Applications

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Explore Other Sets

Get the React & JavaScript PDF — Free

React & JavaScript
Question Set