20 Most Asked JavaScript Interview Questions & Answers [2025]

Navigating the world of JavaScript can be an exciting journey, especially when you're on the cusp of entering the job market. As a versatile and widely-used programming language, JavaScript continues to be a vital skill set for web developers. Aspiring developers need to thoroughly understand JavaScript to excel in their interviews.

JavaScript is a programming language used to make web pages interactive and dynamic. It enables the inclusion of complex features on web pages, making them more user-friendly and engaging. However, mastering JavaScript can be a bit tricky due to its unique quirks and complex structure. Therefore, it's crucial to prepare yourself well before facing the interviewer.

In this article, we will delve into the 20 most frequently asked JavaScript interview questions and provide brief yet informative js interview questions and answers. For a deeper understanding and comprehensive preparation, consider taking JavaScript Training in Noida at Croma Campus, a well-known training institute, which can be a beneficial move.

Top 20 JavaScript Interview Questions And Answers

1. What is JavaScript?

JavaScript is a high-level, interpreted scripting language mainly used for enhancing web pages to offer a more interactive and user-friendly experience.

2. What are JavaScript Data Types?

JavaScript includes several data types including Number, String, Boolean, Object, Undefined, and Null.

3. What's the difference between '==' and '==='?

The operator '==' checks only for equality in value, while '===' checks for both equality in value and type, ensuring stricter equivalence.

4. What is a closure in JavaScript?

A closure is a function defined within another function and has access to the parent function's variables and scope.

5. What is the use of 'This' keyword?

'This' keyword refers to the object from which it was called, giving developers more control over object-oriented programming.

6. What is a 'callback' function in JavaScript?

Callback function is a function passed into another function as an argument, which is then invoked within the outer function.

7. What is 'Hoisting' in JavaScript?

Hoisting is JavaScript's behavior of moving declarations to the top of their respective scopes during the compile phase, before the code execution.

8. What are JavaScript Promises?

Promises in JavaScript are objects that represent the eventual outcome of an asynchronous operation.

9. Explain 'Prototype' in JavaScript?

A 'prototype' in JavaScript is a property associated with every function, containing an object used for inheritance.

10. What are JavaScript arrow functions?

Arrow functions offer a shorter syntax for writing function expressions by omitting the 'function' keyword.

11. What is 'NaN'?

'NaN' stands for Not-a-Number. It results from an invalid or undefined mathematical operation.

12. What is the 'DOM' in JavaScript?

DOM stands for Document Object Model, which is an interface for web documents, representing the structure of a document.

13. What are JavaScript cookies?

Cookies are data stored on a user's computer while browsing a website, enabling the site to remember user preferences or sessions.

14. How can you create an object in JavaScript?

Objects in JavaScript can be created using the object literal or the 'new' keyword.

15. What is the difference between 'null' and 'undefined'?

'Null' is an assignment value that represents no value or no object. 'Undefined' means a variable has been declared but hasn't been assigned a value yet.

16. What is 'event bubbling'?

Event bubbling is a type of event propagation in the HTML DOM API when an event propagates upward from the event target.

17. How does JavaScript handle AJAX requests?

JavaScript uses the XMLHttpRequest object to handle AJAX requests for asynchronous communication with server-side scripts.

18. What is 'localStorage' in JavaScript?

'localStorage' is a part of the Web Storage API that allows JavaScript sites to store data in a user's browser, surviving browser sessions.

19. What is the scope of a variable in JavaScript?

The scope of a variable in JavaScript refers to its accessibility. It can be either global (accessible everywhere) or local (accessible within a function).

20. What is JSON in JavaScript?

JSON stands for JavaScript Object Notation. It is a lightweight data-interchange format that's easy to understand and write.

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Preparing for JavaScript Interview Questions

Before your JS interview, spend quality time understanding the basics of JavaScript. You should be able to explain concepts clearly and provide examples. Work on personal projects or contribute to open-source projects to gain practical experience.

Consider enrolling in JavaScript Online Course at Croma Campus, a renowned training institute that offers comprehensive JavaScript courses with js interview questions preparation. This could significantly improve your understanding of JavaScript and help you answer javascript interview questions more confidently.

Conclusion

Remember, cracking JavaScript interviews requires a good blend of theoretical knowledge and practical experience. This list of js interview questions and answers should serve as a guide for your preparation, but it's by no means exhaustive. For hands-on experience and more comprehensive preparation, consider JavaScript training at Croma Campus. They will equip you with the skills needed to confidently answer these javascript interview questions and more, increasing your chances of acing your interview. Best of luck, and happy learning!