Originally published at: http://www.sitepoint.com/whats-new-in-angularjs-2/
AngularJS has become one of the most popular open source JavaScript frameworks in the world of web application development. Since its inception, it has witnessed phenomenal growth in terms of adoption and community support—both from individual developers and corporations.
From humble beginnings, Angular has matured into a client-side MVW framework (that’s Model-View-Whatever) for the building of complex single-page applications. It places equal importance on application testing and application writing, while simplifying the development process.
The current version of Angular is 1.3. This version is both stable and performant and is used by Google (the framework’s maintainers) to power a great many of their applications (it’s estimated that that there are over 1600 apps inside of Google running on Angular 1.2 or 1.3).
Angular 2.0 was officially announced at the ng-conference in October, 2014. This version won’t be a complex major update, rather a rewrite of the entire framework and will include breaking changes!
Why Angular 2.0?
Before getting into further discussion about Angular 2.0 (which has an estimated release date of the end of 2015), let’s briefly consider the philosophy behind the new version. Angular 2.0 development was started to address the following concerns:
Mobile
The new Angular version will be focused on the development of mobile apps. The rationale is that it’s easier to handle the desktop aspect of things, once the challenges related to mobile (performance, load time, etc.) have been addressed.
Modular
Various modules will be removed from Angular’s core, resulting in better performance. These will find their way into Angular’s ever-growing ecosystem of modules, meaning you’ll be able to pick and choose the parts you need.
Modern
Angular 2.0 will target ES6 and “evergreen” modern browsers (those automatically updated to the latest version). Building for these browsers means that various hacks and workarounds that make Angular harder to develop can be eliminated allowing developers to focus on the code related to their business domain.
What’s the Controversy?
During the ng-conference there was no mention of a migration path to version 2.0. It was also pointed out that the jump to 2.0 version will lead to broken Angular 1.3 apps, as there won’t be any backwards compatibility. Since then, the developer community has been abuzz with uncertainty and speculation, with some developers questioning if it’s even worth starting a new Angular 1.3 project.
What Are the Changes?
AtScript
AtScript is a superset of ES6 and it’s being used to develop Angular 2.0. It’s processed by the Traceur compiler (along with ES6) to produce ES5 code and uses TypeScript’s type syntax to generate runtime type assertions instead of compile time checks. However, AtScript isn’t compulsory—you will still be able to use plain JavaScript/ES5 code instead of AtScript to write Angular apps.
Improved Dependency Injection (DI)
Dependency injection (a software design pattern in which an object is passed its dependencies, rather than creating them itself) was one of the factors that initially differentiated Angular from its competitors. It is particularly beneficial in terms of modular development and component isolation, yet its implementation was plagued with problems in Angular 1.x. Angular 2.0 will will address these issues, as well as adding missing features such as child injectors and lifetime/scope control.
Annotations
AtScript provides tools for associating metadata with functions. This facilitates the construction of object instances by providing the required information to the DI library (which will check for associated metadata when calling a function or creating an instance of a class). It will be also easy to override parameter data by supplying an Inject annotation.
Child Injectors
A child injector inherits all the services of its parent with the capability of overriding them at the child level. According to requirement, different types of objects can be called out and automatically overridden in various scopes.
Instance Scope
The improved DI library will feature instance scope control, which will become even more powerful when used with child injectors and your own scope identifiers.
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