Switching to Angular 2

Switching to Angular 2 by Minko Gechev

In the past I spent some time trying to get up to speed with Angular 1, and after some announcements at Xmas time about the progress being made on Angular 2, I decided it was time to see how things have changed between the major releases. I ordered this book, but had to wait until April before it was published. In the meantime Angular 2 has moved to being very close to full release – the recent ng-conf keynote explains this.

In short, the differences are very great… Angular 2 is very much aimed at being tooling friendly, giving it, as commented in a recent podcast I listened to, more of a Visual Basic RAD feel with proper components each with a lifecycle, inputs and outputs [though I know of no tools so far that support it]. Moreover there is support for server side rendering of the initial page to avoid the delays as the page boots [so called Angular Universal], and also the possibility of the page using web workers for doing the computation.

Chapter 1 of the book is really good discussion of the current state of the web, and the lessons learned from experience with Angular 1, all of which have lead to the modified design of Angular 2. Some concepts from Angular 1, like the notion of scope have been removed, some important concepts like dependency injection have kept but made easier to use, and the framework has been redesigned to make it easier to support server-side rendering.

Chapter 2 takes us through the basic concepts of Angular 2. There’s a big emphasis on building user interfaces via composition. Indeed in Angular 2, we have Directives which have no view and Components which do. Services and Dependency Injection still play a role, but features such as change detection are much simpler and more user optimisable – detection can be turned off, customised in various ways, and the framework also knows about various persistent [functional] data types which make change detection much quicker. The whole digest cycle of Angular 1 is gone – zones, which are explained here, can be used to capture state transitions that may change the state of the user interface. Templates remain for Components to express their views, though filters have been replaced by a richer notion of Pipes.

Angular 2 aims to be a lot more declarative [think tool support again]. Though everything can be transpiled down to more primitive versions of JavaScript, there is an emphasis in the book on using TypeScript which already supports some proposed extensions to JavaScript such as decorators. Chapter 3 of the book takes us through the TypeScript language, with its classes, interfaces, lambda expressions and generics.

Chapter 4, Getting Started with Angular 2 Components and Directives, digs into the building blocks of your Angular applications. We start with a basic hello world application, and the author explains how to get it running using code from his GitHub repository. We then move on to a ToDo application. This application emphasises breaking down the application into components that are connected together. For example, the input box for adding a ToDo, raises an event that is handled by another component in the GUI. The chapter covers projection and the ViewChildren and the ContentChildren decorators. This chapter also takes us through the lifecycle of the component, describing the eight basic lifecycle events that the component can optionally handle, and then the tree style change detection that we now get from the framework – no more multiple change detection passes bounded with a maximal number of passes.

Chapter 5 goes through dependency injection in Angular 2. We now use an injector [which can have a parent and children] to control the scope of injectable classes, and we use decorators to declare the injected items. Again, this decorator syntax can be expressed using a lower level internal DSL if you do not want to use these higher level facilities.

Chapter 6 looks at Angular Forms, which allow you to write the type of GUI you’ll need for the CRUD parts of your application in a fairly declarative manner, explains the validator framework and how you can write your own validators. The second part of the chapter looks at routing.

Chapter 7 explains pipes and how you communicate with stateful services. In this part we have a quick look at async pipes and observables.

The last chapter looks at server side rendering and the developer experience. There are now command line tools for quickly starting a new Angular project.

I though the book was a really good read. It seemed to cover the concepts quite concisely, and the examples made the concepts clear and understandable. It emphasised modern JavaScript and showed the flaws of the Angular 1 design. Now I need to put this all into practice writing some large application.

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