Welcome to domain-driven design in JavaScript. In this book, we will explore a practical approach to developing software with advanced business logic. There are many strategies to keep development flowing and the code and thoughts organized, there are frameworks building on conventions, there are different software paradigms such as object orientation and functional programming, or methodologies such as test-driven development. All these pieces solve problems, and are like tools in a toolbox to help manage growing complexity in software, but they also mean that today when starting something new, there are loads of decisions to make even before we get started at all. Do we want to develop a single-page application, do we want to develop following the standards of a framework closely or do we want to set our own? These kinds of decisions are important, but they also largely depend on the context of the application, and in most cases the best answer to the questions is: it depends.

So, how do we really start? Do we really even know what our problem is, and, if we understand it, does this understanding match that of others? Developers are very seldom the domain experts on a given topic. Therefore, the development process needs input from outside through experts of the business domain when it comes to specifying the behavior a system should have. Of course, this is not only true for a completely new project developed from the ground up, but also can be applied to any new feature added during development of to an application or product. So, even if your project is well on its way already, there will come a time when a new feature just seems to bog the whole thing down and, at this stage, you may want to think about alternative ways to go about approaching this new piece of functionality.

Domain-driven design gives us another useful piece to play with, especially to solve the need to interact with other developers, business experts, and product owners. As in the modern era, JavaScript becomes a more and more persuasive choice to build projects in and, in many cases like browser-based web applications, it actually is the only viable choice. Today, the need to design software with JavaScript is more pressing than ever. In the past, the issues of a more involved software design were focused on either backend or client application development, with the rise of JavaScript as a language to develop complete systems in, this has changed. The development of a JavaScript client in the browser is a complex part of developing the application as a whole, and so is the development of server-side JavaScript applications with the rise of Node.js. In modern development, JavaScript plays a major role and therefore needs to receive the same amount of attention in development practices and processes as other languages and frameworks have in the past. A browser based client-side application often holds the same amount, or even more logic, than the backend. With this change, a lot of new problems and solutions have arisen, the first being the movement toward better encapsulation and modularization of JavaScript projects. New frameworks have arisen and established themselves as the bases for many projects. Last but not least, JavaScript made the jump from being the language in the browser to move more and more to the server side, by means of Node.js or as the query language of choice in some NoSQL databases. Let me take you on a tour of developing a piece of software, taking you through the stages of creating an application from start to finish using the concepts domain-driven design introduced and how they can be interpreted and applied.

In this chapter, you will cover: