JavaScript (Node.js) Interview: 200 Questions and Answers

The book «JavaScript (Node.js) Interview: 200 Questions and Answers» is a comprehensive collection created specifically for developers preparing for technical interviews for Junior and Middle positions. The author has gathered the most common and tricky questions asked in interviews at Russian and international IT companies and provided detailed, structured answers with code examples.

The book covers all key topics necessary for successfully passing an interview:

• JavaScript Basics: data types, closures, prototypes, asynchrony (Event Loop, Promise, async/await), this, scopes.
• Advanced Concepts: functional programming, currying, memoization, design patterns, memory management and optimization.
• Node.js: architecture, modules (CommonJS, ESM), streams, buffers, file system operations, clustering, EventEmitter.
• Databases and Interaction: SQL and NoSQL (MongoDB, PostgreSQL), ORM, connection pooling, transactions.
• Tools and Ecosystem: npm/yarn, Webpack, Babel, ESLint, testing (Jest, Mocha), Docker, CI/CD.
• System Design: REST, GraphQL, microservices, caching (Redis), load balancing, security (JWT, OAuth, XSS, CSRF).

Each question is accompanied not only by the correct answer but also by an explanation of why that answer is correct, as well as alternative approaches. This helps not just to memorize but to deeply understand the material and be prepared for unexpected follow-up questions from the interviewer.

Who this book is for:

• Junior developers who want to systematize their knowledge and confidently pass their first interview.
• Experienced (Middle) developers who want to refresh their knowledge or prepare for a move to a larger company.
• Those transitioning from other languages (Python, Java, PHP) to JavaScript/Node.js and wanting to quickly learn the specifics of the ecosystem.

What you will learn after reading:

• How to confidently answer questions about the Event Loop, closures, prototypal inheritance, and asynchrony.
• How to solve typical algorithmic and logic problems often encountered in interviews.
• How to design scalable applications in Node.js and explain architectural decisions.
• What questions are asked about security, testing, and deployment — and how to answer them.
• How to behave in an interview, what questions to ask the employer, and what to pay attention to when choosing an offer.

The book is written in simple and understandable language, with an emphasis on practice. All code examples are relevant for modern versions of Node.js (18+) and the ES2022+ standard. This is not just a cheat sheet, but a full-fledged textbook that will remain with you as a reference for years to come.

Don't leave your interview preparation to the last minute. Start reading right now — and your next interview will go brilliantly!