In this chapter, we considered the main reasons behind the decisions taken by the Angular core team and the lack of backward compatibility between the last two major versions of the framework. We saw that these decisions were fueled by two things-the evolution of the Web and the evolution of the frontend development, with the lessons learned from the development of AngularJS applications.

In the first section, we learned why we need to use the latest version of the JavaScript language, why to take advantage of Web Components and Web Workers, and why it's not worth it to integrate all these powerful tools in version 1.

We observed the current direction of frontend development and the lessons learned in the last few years. We described why the controller and scope were removed from Angular 2, and why AngularJS's architecture was changed in order to allow server-side rendering for SEO-friendly, high-performance, single-page applications. Another fundamental topic we took a look at was building large-scale applications, and how that motivated single-way data flow in the framework and the choice of the statically typed language, TypeScript.

In the next chapter, we will take a look at the main building blocks of an Angular application, how they can be used and how they relate to each other. The new Angular reuses some of the naming of the concepts introduced by AngularJS, but generally changes the building blocks of our single-page applications completely. We will take a peek at the new concepts and compare them with the ones in the previous version of the framework. We'll make a quick introduction to modules, directives, components, routers, pipes, and services, and describe how they could be combined for building classy, single-page applications.