Components instead of Controllers

While Components have been around in some shape or form around the web, Angular 2 is based around these amazingly flexible elements.

Components in AngularJS 2 will entirely replace controllers. In fact, they will also replace the concept of a module. They look like a directive, but actually act like a controller.

A component is essentially an HTML element that uses Shadow DOM to encapsulate its own scope and behavior. What this really means: your component has its own variable scope. What happens in your component, stays in your component. You can however inject your components into other components or decorate them to add functionality.

Here is an example of the previous burrito example above implemented in AngularJS 2 showing a component in action:

Decorators via Annotations

Decorators are a simple design pattern that we can now use to update the values and context of a component without introducing new behavior.

Seriously, this is great. You can just apply a decorator to your directive and change its variable values without actually tearing into its guts. Change your components color from ‘Red’ to ‘Blue’ at runtime externally without hacking away at its internal functionality or exposing some getter after the fact.

Currently, this is available in the upis provided by TypeScript, but is

A Focus on Dependency Injection

AngularJS 1.x certainly used the concept of dependency injection and promoted it with the usage of services and factories. I don’t think I need to spend a lot of time stumping why and how this can make for better encapsulation and easier re-use of code.

AngularJS 2 will take this a step further and encourage you to use dependency injection with components. Write a login component and inject it into

Zones.js

Previously, we needed to let the Digest / Apply loop cycle through your variables, or use the oft-maligned scope.$apply to let your app know that something changed. ZoneJS will now be handling all of this.

Zones is able to encapsulate the entire scope of your component and is aware of when asynchronous events start and stop.

While getting away from $apply and not having to worry about your scope is great, here comes the best part: ZonesJS will speed up execution time as much as 5x compared to AngularJS 1.x code.

Here is a great talk about Zones by Brian Ford given at the 2015 ng-conf.

The bad news: Zones is only available for modern evergreen browsers. This means if you are using IE10 or below you will not get the to use this amazing toolset. Angular 2 will have fallbacks with dirty value checking and poly-fills to make sure this is all invisible for you, but you will not see the major speed increase you would get from actually using ZonesJS.

TypeScript

TypeScript is a superset of ES6 and gives us some amazing features.

AngularJS 2 will be written in TypeScript, but this doesn’t mean you have to use it. I can say that I plan on using it as I think this will be an area

Ok, this sounds great. How do I prepare to upgrade?

I won’t go too much in depth on this but there will be upgrade paths and plans if you dont want to just ‘start over’ with your existing angular app.

The Official AngularJS 1.x to 2 Upgrade Strategy Doc offers some insight on how to upgrade.