JavaScript Interview Mastery: 1000+ Questions from Junior to Senior

First of all, welcome everybody!

This course is intended to help you pass the JavaScript interview process, together with the most popular frameworks and tools – React, Next.js, NestJS, and TypeScript. Questions are covering positions from Junior to Senior developer.

I’ve been doing interviews for the last 2 years, first within the companies I have worked and now also professionally for other companies.

During my interviewer career I have interviewed about 200 candidates. This course is collection of questions I have asked candidates and questions I was asked when applying for positions.

Why This Course Exists

Since I conduct technical interviews regularly, I’ve seen a lot of candidates – some brilliant, some still struggling with basics. So what’s the catch? In my opinion it is Preparation.

Most candidates fail not because they can’t code, but because they:

• Can’t explain concepts, because they think theory is not important
• Haven’t practiced articulating their knowledge
• Don’t know what interviewers actually ask
• Missed fundamental topics they assumed they knew

This course shows real questions that I ask and questions I’ve been asked or my colleagues were asked. A real interview preparation.

What Makes This Course Different

1. Real Interview Questions

These aren’t textbook definitions. These are actual questions from real JavaScript developer interviews – from startups to enterprise companies. I guess I couldn’t have covered them all, but I really tried to cover as much as I can.

2. Covers All Levels

Questions range from junior basics to senior-level architecture. Each section clearly indicates difficulty level so you know what to expect at your target position.

3. Full Stack Coverage

Dedicated sections for React, Next.js, NestJS, and TypeScript – the most in-demand JavaScript technologies. Over 400 framework-specific questions.

4. Explanations, Not Just Answers

Every answer includes context. You’ll understand why something works, not just what to say. If you have learned through Microsoft preparation guides, it is pretty much similar, you have a question and you have a explanation.

Who This Course Is For

• Junior developers preparing for their first JavaScript job
• Mid-level developers looking to move up
• Senior developers brushing up before interviews
• Self-taught programmers who want to fill knowledge gaps
• Bootcamp graduates preparing for the job market
• Anyone switching to JavaScript from another language

Course Structure

The course is divided into 18 focused sections, totaling 1000+ questions:

Core Language (Sections 1-9)

• Core JavaScript Fundamentals – Data types, variables, operators, control flow, type coercion
• Functions, Closures & Prototypes – Declarations, arrow functions, closures, scope chain, this binding
• Arrays, Objects & Destructuring – Array methods, object manipulation, spread/rest, deep copy
• Async JavaScript – Event loop, Promises, async/await, microtasks vs macrotasks
• ES6+ Modern Features – Map/Set, modules, Proxy/Reflect, optional chaining
• OOP & Design Patterns – Classes, inheritance, Singleton, Factory, Observer, Strategy
• Error Handling & Debugging – try/catch, custom errors, DevTools, source maps
• TypeScript Essentials – Types, generics, utility types, type guards, advanced types
• DOM, Browser APIs & Web Platform – DOM manipulation, events, storage, Web Workers

Runtime & Frameworks (Sections 10-15)

• Node.js Core – Architecture, modules, streams, child processes, cluster
• Node.js APIs & Express – REST APIs, middleware, authentication, databases
• React Fundamentals – Components, hooks, state, effects, Context API
• React Advanced Patterns – Custom hooks, performance, state management, Server Components
• Next.js – App Router, SSR/SSG/ISR, Server Actions, caching
• NestJS – Modules, DI, guards, pipes, interceptors, microservices

Professional Skills (Sections 16-18)

• Testing – Jest, Vitest, React Testing Library, Cypress, Playwright, TDD
• Performance, Security & Architecture – Core Web Vitals, caching, XSS/CSRF, monorepos, DDD
• DevOps, Tooling & AI – Webpack, Vite, Docker, CI/CD, AI-assisted development

How to Use This Course

If You’re a Junior Developer

Start with Sections 1-4 (Core JavaScript, Functions, Arrays, Async). These are your foundation. Master these before moving to frameworks. Focus on understanding concepts deeply rather than memorizing answers.

If You’re Mid-Level

You probably know the basics. Focus on Sections 5-6 (ES6+ and Design Patterns), then dive into the framework sections (12-15) relevant to your target job. Don’t skip TypeScript (Section 8) – it’s required in almost every modern JavaScript role.

If You’re Senior Level

Review everything, but spend extra time on Sections 13 and 17 (Advanced React Patterns, Performance/Security/Architecture). Senior interviews focus heavily on system design and decision-making. Be ready to explain trade-offs, not just solutions.

General Tips

• Don’t just read – practice speaking answers aloud. Interviews test communication, not just knowledge.
• Take the quizzes seriously. If you can’t answer without looking, you’re not ready.
• Focus on “why” not just “what”. Interviewers dig deeper. Know the reasoning behind concepts.
• Review your weak areas multiple times. Repetition builds confidence.

Question Difficulty Levels

Throughout the course, questions are marked by difficulty:

• Junior – Expected knowledge for entry-level positions
• Mid – Expected for developers with 2-4 years experience
• Senior – Expected for senior roles and technical leads

Even if you’re targeting a junior role, reviewing mid-level questions will make you stand out. If you’re going for senior, you should be able to answer junior and mid questions effortlessly.

A Word on Memorization vs Understanding

This course has 1000+ questions. Do not try to memorize all of them.

The goal is understanding. When you truly understand a concept, you can answer any variation of a question about it. When you only memorize, one unexpected angle throws you off.

Use the questions to:

• Identify gaps in your knowledge
• Practice explaining concepts clearly
• Build confidence through repetition
• Learn what interviewers actually care about

Ready to Start?

Your next JavaScript interview doesn’t have to be stressful. With proper preparation, you’ll walk in confident, answer questions clearly, and stand out from other candidates.

Let’s begin with Section 1: Core JavaScript Fundamentals.

Good luck – though with this preparation, you won’t need it.

Your Interview Coach, Simo Jakovic

P.S. The best time to prepare for an interview is before you need one. Start now, not when you’re desperate.