Important JavaScript Question for Interview 🤔

1. What are the differences between var, let, and const?

• How are they used?
• What is their scope and hoisting behavior?

2. Explain closures in JavaScript.

• What is a closure, and how does it work?
• Can you provide an example where closures are useful?

3. What is the event loop in JavaScript?

• How does JavaScript handle asynchronous operations with the event loop?
• What is the call stack and the callback queue?

4. What is this in JavaScript?

• How is this determined in different contexts (like in a method, function, or arrow function)?

5. What is the difference between == and === in JavaScript?

• When would you use one over the other?

6. What is a promise in JavaScript?

• How do promises work?
• How are they different from callbacks?

7. What are JavaScript modules and how do they work?

• Can you explain import and export statements?
• What are named exports vs default exports?

8. What is event delegation?

• How does event delegation improve performance in JavaScript?

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9. What is the difference between null and undefined?

• When would you use each of them?

10. What are arrow functions and how do they differ from regular functions?

• What is the difference in behavior of this in arrow functions versus traditional functions?

11. Can you explain the concept of “hoisting” in JavaScript?

• Which variables and functions are hoisted, and what behavior can you expect?

12. What are higher-order functions in JavaScript?

• Can you provide an example of a higher-order function?

13. What is the bind() method in JavaScript?

• How does bind() work, and when would you use it?

14. What are JavaScript data types?

• Can you list the primitive data types and non-primitive data types in JavaScript?

15. What is the difference between Object.freeze() and Object.seal()?

• How do these methods work, and how are they different?

16. Explain the concept of “prototypal inheritance” in JavaScript.

• How does inheritance work in JavaScript using prototypes?

17. What is the setTimeout() and setInterval() function in JavaScript?

• How are they different from each other, and how do you use them?

18. How does JavaScript handle asynchronous code?

• What are callbacks, promises, and async/await? How are they different from one another?

19. What is the spread operator (...) in JavaScript?

• How does it work with arrays and objects?

20. What are the new features introduced in ES6?

• Can you list some of the important ES6 features, like template literals, destructuring, promises, etc.?

These questions cover a wide range of topics that are commonly asked in JavaScript interviews, from basic concepts to more advanced topics. Try to explain the answers clearly and provide examples when possible to demonstrate your understanding. Best of luck with your interview preparation! 🎉