MOST ASKED JAVASCRIPT INTERVIEW QUESTIONS

Top 50 JavaScript Interview Questions for Experienced Professionals

You don’t want to skip these questions if you’re preparing for JavaScript Interviews

Previously I have shared important interview questions for ASP.NET and MS SQL SERVER. Here’s the list of 50 most asked questions related to JavaScript that you must not skip at any cost if you want to excel your interview.

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1. What are the differences between var, let , and const?
2. Explain the concept of hoisting in JavaScript.
3. What is the difference between `==` and `===`? ( I think this is the most asked questions)
4. How does JavaScript handle asynchronous code?
5. What is a closure, and how is it used in JavaScript?
6. What is the purpose of the this keyword?
7. How does event delegation work in JavaScript?
8. What are JavaScript prototypes, and how do they work?
9. Explain the concept of JavaScript scope.
10. What is the difference between null and undefined?
11. What is a promise, and how does it work?
12. What is the difference between Array.prototype.map and Array.prototype.forEach?
13. What are arrow functions, and how do they differ from traditional functions?
14. How can you handle errors in JavaScript?
15. What are the different ways to create an object in JavaScript?
16. Explain the `bind`, `call`, and `apply` methods.
17. What is the purpose of the `spread` and `rest` operators?
18. What is the difference between synchronous and asynchronous execution?
19. How do you check if a variable is an array in JavaScript?
20. What are JavaScript data types?

Intermediate Questions

21. What is a callback function, and when would you use one?

22. Explain the concept of event bubbling and capturing.

23. How do you create a JavaScript class, and what are its benefits?

24. What is the fetch API, and how does it differ from XMLHttpRequest?

25. How does the JavaScript event loop work?

26. What is the purpose of the async and await keywords?

27. How do you manipulate the DOM using JavaScript?

28. What is a JavaScript module, and how do you use import and export?

29. What is the difference between `Object.assign` and the spread operator for objects?

30. How can you optimize the performance of a JavaScript application?

31. Explain the concept of memoization and its use case.

32. What is the Symbol type in JavaScript, and when would you use it?

33. What are `set` and `map` data structures in JavaScript?

34. How do you implement inheritance in JavaScript?

35. Explain the use of Object.create in JavaScript.

36. How can you use JavaScript to make HTTP requests?

37. What is the difference between `Function.prototype.apply` and `Function.prototype.call`?

38. How do you handle promises in JavaScript, and what are `Promise.all` and `Promise.race`?

Advanced Questions

39. Explain the concept of a JavaScript generator function.

40. How does JavaScript achieve object-oriented programming with prototypal inheritance?

41. What are JavaScript decorators, and how can they be used?

42. Describe how you would implement a custom event system in JavaScript.

43. What is the purpose of the `Proxy` object in JavaScript, and how can it be used?

44. How does the `WeakMap` and `WeakSet` work, and when would you use them?

45. Explain the concept of `Service Workers` and how they are used in Progressive Web Apps (PWAs).

46. What is `WebAssembly`, and how does it relate to JavaScript?

47. How does JavaScript handle memory management and garbage collection?

48. Describe the `Observable` pattern and its implementation in JavaScript.

49. What are the different ways to optimize JavaScript code performance, and what tools can assist with this?

50. How would you handle state management in a large JavaScript application?

Bonus Questions

1. You have a web application where users can add and remove items from a shopping cart. How would you ensure that the cart’s state is managed efficiently and updated across different parts of the application?
2. You need to implement a feature where a user can upload a file, and you want to provide a progress bar indicating the upload status. How would you approach this problem using JavaScript?

These questions should provide a solid foundation for preparing for JavaScript interviews, ranging from fundamental concepts of JavaScript. I have also noticed that many of these questions are common for other interviews as well like for angular developer.