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ES6 Interview Questions and Answers

This page contains a comprehensive collection of ES6 Interview Questions and Answers designed for students, freshers, frontend developers, and experienced JavaScript professionals preparing for technical interviews. The guide covers modern JavaScript features introduced in ECMAScript 2015 (ES6) with practical explanations and real-world examples.

ES6 transformed JavaScript development by introducing cleaner syntax, better modularity, asynchronous programming improvements, and powerful language features. Today almost every modern JavaScript framework, including React, Angular, Vue.js, Node.js, and Next.js, relies heavily on ES6 concepts.

Whether you're preparing for frontend, full-stack, or JavaScript developer interviews, these ES6 interview questions will help you strengthen your understanding of modern JavaScript programming and improve your confidence during coding interviews.

Difficulty
Beginner to Advanced
Topics Covered
Core ES6 Features
Examples
Modern JavaScript
Updated
July 2026

Why Learn ES6?

ES6 introduced major improvements that made JavaScript easier to read, write, and maintain. Features such as let,const, arrow functions, template literals, destructuring, promises, modules, and classes have become standard in modern web development.

Interviewers frequently ask ES6 questions because modern JavaScript applications rely heavily on these concepts. Understanding ES6 helps developers write cleaner, reusable, and more efficient code while building scalable applications.

Topics Covered

  • let and const
  • Arrow Functions
  • Template Literals
  • Destructuring Assignment
  • Spread Operator
  • Rest Parameters
  • Default Parameters
  • Promises
  • Modules (Import & Export)
  • Classes
  • Iterators & Generators
  • Maps & Sets
  • Symbols
  • Modern JavaScript Best Practices
Beginner
1. What is JavaScript?
JavaScript is a scripting language used to create dynamic and interactive web pages.
Beginner
2. Is JavaScript a compiled or interpreted language?
JavaScript is an interpreted language executed by the browser.
Beginner
3. What are variables in JavaScript?
Variables store data values using var, let, or const.
Beginner
4. Difference between var, let, and const?
var is function-scoped, let and const are block-scoped.const cannot be reassigned.
Beginner
5. What are data types in JavaScript?
String, Number, Boolean, Null, Undefined, Object, Symbol, BigInt.
Beginner
6. What is a function?
A reusable block of code designed to perform a task.
Beginner
7. What is an array?
An array stores multiple values in a single variable.
Beginner
8. What is an object?
An object is a collection of key-value pairs.
Beginner
9. What is DOM?
DOM (Document Object Model) represents HTML elements as objects.
Beginner
10. What is an event?
An action that occurs in the browser, like click or submit.
Beginner
11. What is null?
null represents an intentional absence of value.
Beginner
12. What is undefined?
A variable declared but not assigned a value.
Beginner
13. What is typeof operator?
It returns the data type of a variable.
Beginner
14. What is NaN?
NaN means "Not a Number", returned for invalid numeric operations.
Beginner
15. What is strict mode?
A mode that helps catch common coding mistakes using "use strict".
Intermediate
16. What is hoisting?
JavaScript moves variable and function declarations to the top of scope.
Intermediate
17. What is closure?
A function that remembers variables from its outer scope.
Intermediate
18. What is scope?
Scope determines where variables are accessible.
Intermediate
19. Difference between == and ===?
== compares values only, === compares value and type.
Intermediate
20. What is a callback function?
A function passed as an argument to another function.
Intermediate
21. What is JSON?
JavaScript Object Notation, used for data exchange.
Intermediate
22. What is promise?
An object representing eventual completion or failure of async operation.
Intermediate
23. What is async/await?
Syntax to handle promises in a cleaner way.
Intermediate
24. What is event bubbling?
Event propagates from child to parent elements.
Intermediate
25. What is event delegation?
Handling events at parent level instead of multiple child elements.
Intermediate
26. What is this keyword?
Refers to the object that is currently executing the function.
Intermediate
27. What is arrow function?
Shorter syntax for writing functions using .
Intermediate
28. What is map()?
Creates a new array by applying a function to each element.
Intermediate
29. What is filter()?
Returns elements that satisfy a condition.
Intermediate
30. What is reduce()?
Reduces array to a single value.
Advanced
31. What is prototype?
Mechanism to share properties between objects.
Advanced
32. What is prototypal inheritance?
Objects inherit properties from another object.
Advanced
33. What is currying?
Transforming a function with multiple arguments into nested functions.
Advanced
34. What is debouncing?
Limits function execution rate after user stops triggering event.
Advanced
35. What is throttling?
Ensures function executes at fixed time intervals.
Advanced
36. What is event loop?
Handles asynchronous callbacks in JavaScript.
Advanced
37. What is call(), apply(), bind()?
Methods to control this context in functions.
Advanced
38. What is memory leak?
When memory is not released after use.
Advanced
39. What is module in JavaScript?
Reusable file exporting functionality using import/export.
Advanced
40. What is IIFE?
Immediately Invoked Function Expression executes instantly.
Coding Round
41. Reverse a string
str.split('').reverse().join('')
Coding Round
42. Check palindrome
str === str.split('').reverse().join('')
Coding Round
43. Find max in array
Math.max(...arr)
Coding Round
44. Remove duplicates
[...new Set(arr)]
Coding Round
45. Merge arrays
[...arr1, ...arr2]
Coding Round
46. Convert string to number
Number(str)
Coding Round
47. Loop through object
Answer Here
Coding Round
48. Delay function execution
Answer Here
Coding Round
49. Fetch API example
Answer Here
Coding Round
50. Create a promise
Answer Here

Continue Your JavaScript Interview Preparation

JavaScript is one of the most widely used programming languages for frontend and backend development. Recruiters also evaluate your knowledge of HTML, CSS, TypeScript, React, Node.js, Git, and web fundamentals. Continue your preparation with these popular interview guides.

TypeScript Interview Questions
React Interview Questions
Node.js Interview Questions
HTML Interview Questions

About This JavaScript Interview Guide

This JavaScript interview guide is designed for educational purposes and helps learners prepare for frontend, backend, and full-stack development interviews. The questions range from beginner to advanced level and focus on concepts that frequently appear in technical interviews at startups and leading technology companies.

Along with theoretical explanations, candidates should practice writing JavaScript code, debugging applications, solving algorithmic problems, and building real-world projects. Hands-on experience with ES6+, asynchronous programming, browser APIs, and modern JavaScript frameworks greatly improves interview performance.

InterviewPitch regularly updates this resource to include the latest JavaScript features, interview trends, coding challenges, and best practices so that both freshers and experienced developers can stay prepared for their next technical interview.