Most asked JavaScript Interview Questions: Part 1

Raghav Bang
Published in
3 min readOct 22, 2022


  1. JavaScript — Singlethread or multithread?
  • JavaScript is always synchronous and single-threaded. If you’re executing a JavaScript block of code on a page, then no other JavaScript on that page will currently be executed.

2. How does JS handles multithread operations?

  • Using Web Workers

3. How does JavaScript works? Tell about the JavaScript engine and call stack.

4. What is event loop?

5. Type of array in JavaScript.

6. Type of null in JavaScript.

  • Object

7. What are callback functions. Why do we use them?

8. Explain Hosting?

9. What is IIFE?

10. Implement a function which takes three parameter - a callback function, delay time and a number n. Which call the function n number of times with delay time interval.

11. Which DS is used in implementing folder structure?

  • Tree

12. What is Block Scope?

13. How are objects created in JS?

14. Difference between == and ===.

Equality comparisons and sameness — JavaScript | MDN (

15. Difference between Local and Session storage.

Local Storage: This read-only interface property provides access to the Document’s local storage object, the stored data is stored across browser sessions.

Window.localStorage — Web APIs | MDN (

Session Storage objects can be accessed using the sessionStorage read-only property. The difference between sessionStorage and localStorage is that localStorage data does not expire, whereas sessionStorage data is cleared when the page session ends.

Window.sessionStorage — Web APIs | MDN (

16. Difference between Async and Differ.

17. What is strict mode in JavaScript?

JavaScript’s strict mode is a way to opt into a restricted variant of JavaScript

Strict mode — JavaScript | MDN (

18. What is “this” in JS?

  • this keyword in javascript always holds the reference to a single object, that defines the current line of code’s execution context. Functions, in JavaScript, are essentially objects. Like objects, they can be assigned to variables, passed to other functions, and returned from functions. And much like objects, they have their own properties. One of these properties is this.

19. What new features were introduced in ES6?

  • The let keyword
  • The const keyword
  • Arrow Functions
  • The … Operator
  • For/of
  • Map Objects
  • Set Objects
  • Classes
  • Promises
  • Symbol
  • Default Parameters
  • Function Rest Parameter
  • String.includes(), etc.

If you like this post and find it helpful you can give me claps and do follow me😍!!

Most asked JavaScript Interview Question: Part 2: Most asked JavaScript Interview Questions: Part 2 | by Raghav Bang | RaghavBang | Oct, 2022 | Medium