JavaScript Mastery: 50 Must-Know Interview Questions for 2024

These questions cover a wide range of topics, from core concepts and advanced features to design patterns, performance optimization, and browser-specific behaviors. They are designed to test the depth of knowledge and practical experience of a senior JavaScript developer.

1. What are the main differences between var, let, and const?
2. Explain closures and provide an example of where they might be used.
3. How does the event loop work in JavaScript?
4. Describe prototypal inheritance and its advantages over classical inheritance.
5. What are promises, and how do they work? Provide an example.
6. Explain the async/await syntax. How does it differ from using promises?
7. What is a JavaScript module, and how do you import and export them?
8. How do destructuring assignments work in JavaScript?
9. Explain the difference between == and ===.
10. What is hoisting in JavaScript?
11. How does JavaScript handle memory management and garbage collection?
12. Explain the purpose of the bind, call, and apply methods.
13. What are generator functions, and how do they work?
14. Describe the concept of higher-order functions.
15. What are Proxy and Reflect in JavaScript, and how are they used?
16. How does the this keyword work, and how can it be manipulated?
17. Explain the concept of event delegation.
18. How do you debounce and throttle functions in JavaScript?
19. What is the difference between synchronous and asynchronous programming in JavaScript?
20. Describe the module pattern and its use cases.
21. What are the benefits of using arrow functions, and what limitations do they have?
22. How does the spread operator work in JavaScript?
23. What is destructuring, and how can it be used with objects and arrays?
24. Explain the concept of template literals and tagged templates.
25. What is the purpose of Symbol in JavaScript?
26. How do default parameters work in functions?
27. What are Map and Set, and how do they differ from objects and arrays?
28. Explain the concept of async iterators and generators.
29. What are WeakMap and WeakSet, and how are they different from Map and Set?
30. Describe how modules work in ES6 and beyond.
31. What is the Singleton pattern, and how is it implemented in JavaScript?
32. Explain the Factory pattern with an example.
33. How do you implement the Observer pattern in JavaScript?
34. Describe the Decorator pattern and its use cases.
35. What is the Module pattern, and how does it help in code organization?
36. Explain the use of the Proxy pattern in JavaScript.
37. How do you implement the Command pattern in JavaScript?
38. What are the benefits of using the Strategy pattern?
39. How do you optimize the performance of a JavaScript application?
40. Explain how lazy loading works in JavaScript.
41. What are Web Workers, and how do they help in performance optimization?
42. How does JavaScript handle asynchronous operations under the hood?
43. What are some common memory leaks in JavaScript, and how can they be avoided?
44. How can you measure and improve the performance of JavaScript code?
45. Explain how the DOM works in JavaScript.
46. How do event propagation and event bubbling work?
47. What are the differences between localStorage, sessionStorage, and cookies?
48. How does the Fetch API work, and what are its advantages over XMLHttpRequest?
49. What is CORS, and how do you handle it in a JavaScript application?
50. How do you implement client-side routing in a single-page application (SPA)?

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