JavaScript Interview Questions and Answers for 2026

JavaScript is the backbone of modern web pages and applications, powering everything from interactive user interfaces to robust backend systems. As a versatile programming language and scripting language, it's essential for both frontend and backend development, making it a must-have skill for developers worldwide. Mastering javascript interview questions is crucial for anyone aiming to land a top developer role.

This guide covers the most relevant javascript interview questions and answers, offering actionable insights and practical code examples. Whether you're freshers entering the field or experienced engineers, you'll be equipped to tackle interviews with confidence.

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JavaScript Interview Questions for Freshers

1. What are the different data types in JavaScript?

JavaScript code has primitive data types and non-primitive data types:

Primitive Data Types:

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Non-Primitive: Objects, arrays, and functions are all object types.

2. What is the difference between == and ===?

This is one of the most common javascript interview questions and answers.

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3. Explain the difference between var, let, and const.

These keywords have different scoping rules:

4. What is hoisting in JavaScript?

Hoisting moves variable declarations and function declarations to the top of their scope during compile-time:

5. What is strict mode?

Strict mode enables restricted Java variant using "use strict":

6. Explain the this keyword.

The this keyword refers to the object executing the current function:

7. What are closures?

Closures occur when functions access variables from outer scope even after outer function execution:

8. What is the difference between function declarations and function expressions?

Function declarations are fully hoisted, while function expressions follow variable hoisting:

9. What are callback functions?

A callback function is passed as argument to another function and executed later:

10. What are higher-order functions?

Higher-order functions take other functions as parameters or return functions:

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Core JavaScript Concepts

11. What is the event loop?

The event loop enables non-blocking asynchronous operations in single-threaded JavaScript:

12. What are promises and async/await?

Promises handle asynchronous operations better than callbacks:

13. What are arrow functions?

Arrow functions provide concise syntax and lexical this binding:

14. What is prototypal inheritance?

JavaScript uses prototypal inheritance where objects inherit from other objects:

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DOM and Web APIs

15. What is the DOM?

The Document Object Model (DOM) represents HTML as objects JavaScript can manipulate:

16. What is the difference between setTimeout and setInterval?

Both handle timing but behave differently:

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Modern JavaScript Features

17. What are template literals?

Template literals enable string interpolation and multi-line strings:

18. What is destructuring?

Destructuring extracts values from arrays or object properties:

19. What is the spread operator?

The spread operator expands iterables and objects:

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Error Handling and Debugging

20. What are the different error types?

JavaScript has several built-in error types:

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Coding Questions

21. What is the output of these code snippets?

Question 1:

Answer: "number", false, returns true (NaN is not a number type but typeof returns "number")

Question 2:

Answer: Prints 3, 3, 3 because var is function-scoped and all callbacks reference the same i.

22. Common Implementation Challenges

Remove duplicates from array:

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Debounce function:

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Conclusion

This guide covers the most frequently asked javascript interview questions across technical interviews. Focus on understanding these core concepts: data types, scope, closures, asynchronous operations, and modern ES6+ features.

Key preparation tips:

• Master fundamentals like hoisting, the this keyword, and prototypal inheritance
• Practice async patterns with promises and async/await
• Understand DOM manipulation and event handling
• Learn modern JavaScript syntax and features
• Practice common coding challenges and output prediction questions

Success in JavaScript interviews comes from solid fundamentals combined with practical problem-solving skills. Keep practicing these concepts and you'll be well-prepared for any technical interview.

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Frequently Asked Questions

What are basic JavaScript interview questions?

Basic JavaScript interview questions cover core concepts like data types using the typeof operator, variable declarations with var keyword, let keyword, and const keyword, and scope differences between global scope and local scope. Common topics include javascript function basics, javascript objects manipulation, array prototype methods, and creating a new array. Interviews often test ECMAScript 2015 features, modules understanding, and basic asynchronous javascript patterns.

How to ace a JavaScript interview?

Master fundamentals: scope (global scope vs local scope), lexical scoping, and runtime behavior with different variable declarations. Practice javascript function implementations and javascript objects manipulation. Understand OOP concepts and array prototype methods. Study modern features like modules, asynchronous javascript, and specialized collections like WeakMap and WeakSet. Know how JavaScript works in browsers and Node.js environments, including CSS integration use case scenarios.

How do you explain "this" in JavaScript?

The "this" keyword in a javascript function refers to the executing object, but its single value depends on the call context. In global scope, "this" is the global object or undefined in strict mode. In javascript objects methods, "this" refers to the owning object. Arrow functions use lexical scoping, inheriting "this" from the enclosing scope. This behavior is consistent across different runtime environments including Node.js.

What is the difference between == and === in JavaScript interview questions?

These comparison operators differ in type handling: == performs type coercion before comparison, while === compares both value and type without coercion. The == operator can produce unexpected results across different data types, while === provides predictable behavior. Use === for most use case scenarios to avoid runtime issues. This applies whether building frontend applications with CSS or backend services with Node.js.

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