A major framework for many years, Angular has in uenced a generation of web tech- nologies. Even developers who haven’t used it have bene tted from its existence, as it helped popularize a number of important concepts and technologies.
Early in its AngularJS days (version 1.x is known as AngularJS), it became perhaps the most popular web application framework of its time. But the 1.x version had lim- itations, and a number of optimizations were built into the framework. The concept of two-way databinding (being able to sync data between the controller and the view automatically), which was touted early on as its best feature, became a performance bottleneck in large applications that abused its utility. To help mitigate this problem, one-way and one-time binding options were introduced to improve performance, but they required developers to opt in. Also, components were introduced as a better way to organize and structure applications, but taking advantage of them required refactoring of existing applications.
You could build an amazing and performant application with AngularJS 1.x, but it wasn’t always the default mode and required unlearning concepts that were believed to be best practices from earlier releases. Simply put, writing well-designed applica- tions was possible because of workarounds from the original concepts that AngularJS embraced.
Instead of evolving the version 1.x codebase, the decision was made to rewrite it from scratch to implement the lessons learned into the foundations of the next major ver- sion. This was a multiyear endeavor that involved both the Angular team at Google and the larger community of early adopters. It was a long journey, and I rode alongside and built applications on top of it during early alpha and beta phases. The nal result of that
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journey was Angular 2.0 (version 2.0 and above is known as just Angular), and its com- munity has grown rapidly since its release.
I started working on Angular in Action while Angular was still in early beta for ver- sion 2.0. Angular then underwent regular and rapid iterations during the book’s writ- ing and development. But today Angular is stable and evolves with a well-de ned release cycle for new features and deprecations. The book examples are written to work with Angular 5 and above, and going forward, the GitHub projects will have notes about any required changes to keep up with Angular’s evolution.
