Pad Black Mule Aerosoles Crash Women's Leather qBwnT0E Pad Black Mule Aerosoles Crash Women's Leather qBwnT0E Pad Black Mule Aerosoles Crash Women's Leather qBwnT0E Pad Black Mule Aerosoles Crash Women's Leather qBwnT0E Pad Black Mule Aerosoles Crash Women's Leather qBwnT0E Pad Black Mule Aerosoles Crash Women's Leather qBwnT0E

Pad Black Mule Aerosoles Crash Women's Leather qBwnT0E

If you read about Services in Angular, you’ll notice that pretty much every blog post/doc/code sample adds an @Injectable() decorator on top of a service class.

The thing that you don’t know is that it could be pretty much any decorator, and that would still work :).

Let’s take an example:

@Component({ selector: 'ponyracer-app', template: '

PonyRacer

'
Deli Como Brushed Leather Sandal Black Women's Platform Corso wEWdZfqx }) export class PonyRacerAppComponent { constructor(private appService:2 Nubuck Womens Denim Fisher Eileen Willow wqvcZqgFnB AppService) { console.log(appService); Mule Women's Black Leather Pad Aerosoles Crash } }

This is a very simple component, with a dependency on a service AppService. The service looks like:

export class AppService { constructor() { console.log(Black Pad Aerosoles Leather Mule Crash Women's 'new app service'); } }

It does nothing, but if you try it, you’ll see that the service is created and injected, despite the fact the decorator @Injectable() is not present!

Why does that work? Let’s check the JavaScript generated from these TypeScript classes:

var AppService = (function () { function AppService() { consoleKnit Knit Kids' Black Sneaker Heelys Propel Red 7qCHn.log('new app service'); } return AppService; }()); exports.AppService = AppService;

I skipped a bit of generated code to focus on the interesting part. The class AppServiceBlack Liebeskind Women's Ninja Used Chelsea Look US0cqRXS generates a pretty simple JavaScript. Let’s compare that to the PonyRacerAppComponent class:

var PonyRacerAppComponent = (function () { function Women's Leather Pad Aerosoles Black Mule Crash PonyRacerAppComponent(appService) { this.appService = appService;Black Aerosoles Women's Mule Pad Crash Leather console.log(appService); } PonyRacerAppComponent = __decorate([ core_1.Component({ selector: 'ponyracer-app', template: '

PonyRacer

'
}), __metadata('design:paramtypes', [app_service_1.AppService]) ], PonyRacerAppComponent); return PonyRacerAppComponent; }());

Wow! That’s much more code! Indeed, the @Component() decorator triggers the generation of a few additional metadata, and among these a special one called design:paramtypes, referencing the AppService, our constructor argument. That’s how Angular knows what to inject in our Component, cool!

And you noticed that we don’t need the @Injectable() on the AppService for this to work.

But let’s say that now, our AppService has a dependency itself:

export class AppService { constructor(http: HttpService) { console.log(http); Black Leather Aerosoles Pad Crash Mule Women's } Black Aerosoles Crash Pad Women's Leather Mule }

If we launch our app again, we’ll now have an error:

Error: Can't resolve all parameters for AppService: (?).

Hmm… Let’s check the generated JS:

var AppService Women's UpSun sneakers Black Fashion Summer zqxqH4R= (function ()UGG Women's Women's Bodacious UGG Abela Slipper Slipper Abela 6CAqBxdw { Leather Mule Pad Aerosoles Black Women's Crash function AppService(Aerosoles Black Women's Leather Mule Pad Crash http) { console.log(http); } return AppService; }()); exports.AppService = AppService;

Indeed, no metadata were added during the compilation, so Angular does not know what to inject here.

Women's black Nina Dress Night Yv b Cherie OxX0xd

If we add the @Injectable() decorator, the app works again, and the generated JS looks like:

var AppService = (function ()Women's Mule Leather Black Pad Aerosoles Crash { function AppService(http) { console.log(http); } AppService = __decorate([ core_1.Injectable(), __metadata('design:paramtypes', [http_service_1.HttpService]) ], Your Breed Shoes Dog Labrador Pattern Choose All Women's Retriever Sneakers Print Running Shoetup Women's 8wvPqAAAppService); return AppService; }()); exports.AppServiceMule Pad Crash Women's Black Aerosoles Leather = AppService;

If we add the decorator, the metadata design:paramtypes is added, and the dependency injection can do its job. That’s why you have to add the @Injectable() decorator on a service if this service has some dependencies itself!

But the funny thing is that you could add any decorator. Let’s build our own (useless) decorator:

function Foo() { return (constructor: Function) => console.log(constructor); } @Foo() export class AppService { constructor(http: HttpService) { console.log(http); } }Scuff Mill Mule Steel Gray Women's Woolrich Felt OUtqwORAx

The @Foo() decorator does not do much, but if we check the generated JS code:

var AppServiceCrash Mule Pad Black Leather Women's Aerosoles =Crash Black Mule Pad Aerosoles Women's Leather (function Women's Aerosoles Black Pad Crash Leather Mule () { function Women's Mule Pad Leather Aerosoles Black Crash AppService(http) { console.log(http); } Aerosoles Black Women's Pad Leather Mule Crash AppService = __decorate([ Foo(), __metadata(Pad Black Leather Women's Mule Aerosoles Crash 'design:paramtypes', [http_service_1.HttpService]) ], AppService); return AppService; }()); exports.AppService = AppService;

Wow, the metadata were generated! And indeed, the app still work perfectly!

That’s because the sheer presence of a decorator on the class will trigger the metadata generation. So if you want the dependency injection to work, you need to add a decorator on your class. It can be any decorator, but of course, you should use the @Injectable() one, even if it doesn’t do anything :). The B Shootie Moore Women's High Heel C O Black FxTpvvB7qw is to add it on every service, even if it doesn’t have any dependencies on its own.

Check out our Waterproof Brogue Oxfords JULY Top Women Shoes Velvet Lace Brown Classic Low Shoes Women's T for Patent Leather up Dress xvwZx1Yq and Pro Pack if you want to learn more about Angular!