This book explains and illustrates how to implement Domain-Driven Design, Command Query Responsibility Segregation and Event Sourcing. The goal is to build software that is behavior-rich, event-based, problem-centric, reactive, scalable and well-designed. Domain-Driven Design is a concept that focuses on the problem space and its associated knowledge areas. Command Query Responsibility Segregation separates a software into a write side and a read side. Event Sourcing is an architectural pattern that represents state as a sequence of immutable events. The concepts are explained in theory and put into practice with standalone examples and a Sample Application. This is done without third-party software. The book comes with a source code bundle and supports interactive execution. All code is written in JavaScript and uses Node.js as runtime.

Style of this book

The primary focus of this book is the application and the implementation of concepts. Therefore, the purely theoretical parts are generally concise. The covered topics are illustrated extensively with a large amount of examples and code. Selected conceptual parts are also discussed in greater detail. Apart from Node.js and JavaScript, the book's main content does not utilize or explain specific frameworks or technologies. For functionalities that require persistence or inter-process communication, exemplary implementations are provided that directly work with the filesystem. This includes Repositories, the Event Store, Read Model stores and a remote event distribution. The goal is to convey a deeper understanding of the according concepts. For production purposes, these implementations can be replaced with suitable technologies. This procedure is exemplified in Appendix B.

The following articles explain selected aspects of the book style in more detail:

• Why my book uses Node.js and JavaScript
• Using the filesystem for illustration purposes