In this chapter, we acknowledged the importance of defining a domain model before starting the development of the app. We used a graphical tool (model concepts) to design a model for categories and links, which can be exported in JSON format. Also, we saw how JSON can be used in Dart. A simple domain model framework Dartlero was explored, and we implemented that in two models: a project model and a category-links model. By doing this, we exercised the knowledge of classes, interfaces, generics, lists, maps, and unit testing that we acquired in Chapter 2, Getting to Work with Dart. The next few chapters are more practical in nature. We learned how to work with the Document Object Model (DOM) in HTML pages, how to build forms, how to draw, and how to use audio and video in web pages.