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

The book "JavaScript (Node.js) Interview: 200 Questions and Answers" is a practical guide for developers preparing for technical interviews for Junior and Middle JavaScript/Node.js developer positions. The author has collected the most common and tricky questions asked in interviews at Russian and international IT companies and provided detailed, structured answers.

What is this book about?

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

• JavaScript Basics: data types, closures, prototypes, this context, hoisting, scopes.
• Asynchrony and Event Loop: promises, async/await, callbacks, microtasks and macrotasks, working with timers.
• Node.js: module system (CommonJS vs ESM), working with streams (Streams), Buffer, file system, processes and clustering.
• Frameworks and Databases: Express.js, routing, middleware, working with PostgreSQL and MongoDB via drivers and ORM/ODM.
• Architecture and Patterns: MVC, Middleware Chain, Observer, Singleton, error handling and logging.
• Testing and Security: Unit tests (Jest), integration tests, protection against XSS, SQL injection, CSRF.
• Algorithmic Problems: typical interview tasks (searching, sorting, working with trees and graphs).

Who is this book for?

• Junior Developers (1–2 years of experience): systematize your knowledge, fill in gaps, and learn to answer questions without panic.
• Middle Developers (3–5 years): deepen your understanding of Node.js internals, prepare for questions about architecture and optimization.
• Team Leads and Mentors: use the book as a basis for conducting internal interviews and training your team.

What will you learn after reading?

• How the Event Loop works and why setTimeout with zero delay does not guarantee immediate execution.
• The difference between require and import, and how Node.js caches modules.
• How to properly handle errors in asynchronous code and avoid "callback hell".
• How to design a REST API that can withstand high load.
• How to answer questions about performance, memory leaks, and profiling.

Each question is accompanied not only by the correct answer but also by an explanation of why that answer is correct, along with code examples. At the end of the book, there is a self-assessment checklist for before the interview and a list of real questions from companies (Yandex, Sber, Tinkoff, Ozon, Wildberries).

This book is your personal trainer before the interview. Read it, and you will feel confident in your knowledge and be able to easily pass any technical interview.