1000+ Core JavaScript Interview Questions

JavaScript is the backbone of modern web development and a critical skill in technical interviews for frontend and full-stack roles. This course provides an in-depth multiple-choice question (MCQ) based approach to help you master Core JavaScript and confidently tackle interview questions.

The course includes 1000+ curated questions, each designed to test and reinforce your understanding of the most important and frequently asked JavaScript concepts. After each question, you'll receive detailed explanations that not only reveal the correct answer but also explain why other options are incorrect — promoting deeper understanding and critical thinking.

Topics covered include variables and scoping, data types, closures, this keyword, asynchronous JavaScript (Promises, async/await), hoisting, prototype chain, ES6+ enhancements, functional programming, and more. Whether you're brushing up for a job interview or aiming to improve your daily coding confidence, this course covers it all.

Unlike passive tutorials, this active learning method will help you retain knowledge longer and spot tricky interview pitfalls more easily. The MCQs range from beginner to advanced levels, allowing learners of all backgrounds to benefit.

This course is ideal for engineers targeting roles at tech companies like Google, Amazon, Microsoft, or startups — or anyone wanting to future-proof their JavaScript knowledge.

By the end, you'll have a sharper, more confident command of JavaScript and be interview-ready.

Topics Are :-

1. Core JavaScript Fundamentals

Topics:

• Data Types & Type Coercion (null, undefined, undeclared, == vs ===, isNaN(), Number.isNaN(), typeof)

• Variables (var, let, const, Hoisting, Scope, TDZ, Redeclaration)

• Operators (Logical, comparison, arithmetic, bitwise, Ternary)

• Control Flow (if/else, switch, loops, break, continue)

• New: Strict Mode ('use strict') - Purpose and implications

• New: eval() and new Function() - When to avoid, security

Difficulty: Basic to Intermediate
MCQ Count: 70 (Slightly increased to cover new points)

2. Functions & Scope

Topics:

• Function Declaration vs. Expression vs. Arrow Functions (this, Hoisting, arguments)

• Scope & Scope Chain (Lexical scoping, Execution Context)

• Closures (Use cases, memory)

• this Keyword (Binding rules, strict mode)

• call(), apply(), bind() (Differences, polyfills)

• Higher-Order Functions (Map, filter, reduce, composition, currying)

• IIFEs, Recursion

Difficulty: Intermediate to Advanced
MCQ Count: 130

3. Object-Oriented Programming (OOP) in JavaScript

Topics:

• Core OOP Concepts (Encapsulation, Inheritance, Polymorphism, Abstraction)

• Object Creation & Class Syntax (Constructor functions, class, super, static, private fields)

• Prototypes & Prototypal Inheritance (Deep dive: proto vs. prototype, chain, instanceof)

• Composition vs. Inheritance (Mixins)

• Design Principles (SOLID - applied to JS)

Difficulty: Intermediate to Advanced
MCQ Count: 150

4. Objects & Property Management

Topics:

• Object Literals, Property Descriptors & Flags (defineProperty, defineProperties)

• Getters and Setters

• Object Manipulation (keys, values, entries, assign, shallow/deep copy, Spread syntax)

• Immutability (freeze, seal, preventExtensions)

• Destructuring Assignment

Difficulty: Intermediate
MCQ Count: 80

5. Asynchronous JavaScript

Topics:

• Event Loop (Call Stack, Web APIs, Task/Microtask Queues)

• Callbacks, Promises (States, then, catch, finally, Promise.all etc.)

• Async/Await (Error handling)

• Generators & Iterators (Advanced use cases)

Difficulty: Intermediate to Advanced
MCQ Count: 140

6. ES6+ Features (Beyond the basics)

Topics:

• Modules (ESM: import/export, dynamic imports, tree shaking)

• Symbols (Well-known Symbols, use cases)

• Proxies & Reflect (Use cases)

• Sets & Maps (WeakSet, WeakMap)

• New: Internationalization (i18n) APIs (Intl.NumberFormat, DateTimeFormat)

• New: Decorators (Concept, Stage 3 proposal, usage)

Difficulty: Advanced
MCQ Count: 90 (Slightly increased for i18n and Decorators)

7. Environment-Specific JavaScript Utilities

Topics:

• New: Browser-side File Handling (File, Blob, FileReader, Downloadable files, File System Access API - conceptual)

• New: Web Streams API (ReadableStream, WritableStream, TransformStream, pipe, tee)

• New: Node.js fs module (Synchronous/Asynchronous, Promises, Basic Node.js Streams)

• New: Web Workers (Concept, communication with main thread)

• New: Typed Arrays and Array Buffers (Handling binary data)

Difficulty: Intermediate to Advanced
MCQ Count: 70 (Increased significantly for these crucial topics)

8. Regular Expressions (Regex)

Topics:

• Basic Patterns & Quantifiers

• Character Classes, Anchors, Groups, Lookarounds

• Flags (g, i, m, u, s, d)

• String methods using Regex (match, search, replace, split)

• RegExp object methods (test, exec)

Difficulty: Intermediate to Advanced
MCQ Count: 50 (New dedicated section)

9. Advanced Concepts & Design Patterns

Topics:

• Memory Management & Garbage Collection (Leaks, identification)

• Event Delegation (Bubbling, Capturing)

• Error Handling (try...catch, Custom Errors)

• Design Patterns (Module, Revealing Module, Singleton, Factory, Observer, Decorator, Proxy, Debouncing/Throttling)

• Currying & Memoization

Difficulty: Advanced
MCQ Count: 100 (Adjusted from 110)