Design Patterns in JavaScript (Node.js)

This book is a practical guide to applying classic and modern design patterns in the JavaScript and Node.js ecosystem. Unlike abstract textbooks, all examples here are built on real backend development tasks: from building API services to working with data streams and asynchronous queues.

Who is this book for?

• JavaScript developers who want to move from writing "scripts" to designing architecture
• Node.js developers facing code scaling and maintenance issues
• Team leads and architects seeking proven solutions for organizing a codebase
• Programmers familiar with OOP but wanting to understand how patterns work in prototype-oriented JavaScript

What you will learn:

• How to implement creational patterns (Singleton, Factory, Builder) in the context of Node.js modules
• Structural patterns (Adapter, Proxy, Decorator) for working with external APIs and middleware
• Behavioral patterns (Observer, Strategy, Chain of Responsibility) for event-driven architecture
• Node.js-specific approaches: Streams, EventEmitter, Promises, and async/await
• How to avoid anti-patterns and "callback hell" in asynchronous code
• SOLID principles and their implementation without classes (via closures and composition)

Edition features:

• Over 40 patterns with complete code listings
• Comparison of ES6 classes and the functional approach
• Examples of integration with popular frameworks (Express, Socket.io, Koa)
• Chapters on testing and refactoring legacy code
• Checklists for choosing a pattern for a specific task

The book is structured from simple to complex: starting with basic patterns that can be applied today, and gradually moving to enterprise-level architectural solutions. Each chapter contains a practical assignment and self-test questions.

This is not just a translation of GoF into JavaScript — it is a thoughtful adaptation of classic solutions to the specifics of Node.js's asynchronous, event-driven model. By the end of the book, you will be able to design systems that are easy to maintain, test, and scale.