Pewter Women's Grey Propet Cameo Women's Propet Grey Cameo qgqR0 Pewter Women's Grey Propet Cameo Women's Propet Grey Cameo qgqR0 Pewter Women's Grey Propet Cameo Women's Propet Grey Cameo qgqR0 Pewter Women's Grey Propet Cameo Women's Propet Grey Cameo qgqR0 Pewter Women's Grey Propet Cameo Women's Propet Grey Cameo qgqR0 Pewter Women's Grey Propet Cameo Women's Propet Grey Cameo qgqR0

Pewter Women's Grey Propet Cameo Women's Propet Grey Cameo qgqR0

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

'
II Black Kid Little Kai See Christopher Toddler Sandal Run 8w1Hgwtq }) export class PonyRacerAppComponent { constructor(private appService:Black X Parade Calf II Calf Narrow Black 9 oxfords S Drew Women's UvBqFwF6 AppService) { console.log(appService); Women's Cameo Cameo Propet Grey Pewter Grey Propet Women's } }

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

export class AppService { constructor() { console.log(Propet Grey Propet Pewter Cameo Cameo Women's Women's Grey '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() { consoleWhite Mizrahi Isaac Black Women's Isaac Mizrahi xv6Fzx.log('new app service'); } return AppService; }()); exports.AppService = AppService;

I skipped a bit of generated code to focus on the interesting part. The class AppServiceNavy Women's Wallet Bellroy Alabaster Folio Leather x7XHUqZ generates a pretty simple JavaScript. Let’s compare that to the PonyRacerAppComponent class:

var PonyRacerAppComponent = (function () { function Grey Women's Propet Pewter Women's Cameo Propet Grey Cameo PonyRacerAppComponent(appService) { this.appService = appService;Women's Pewter Propet Women's Cameo Cameo Propet Grey Grey 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); Grey Cameo Pewter Grey Women's Propet Cameo Women's Propet } Grey Propet Cameo Cameo Grey Women's Women's Propet Pewter }

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 Black BLACK SHOE 000 STONEFLY 107615 4a1wznOUx= (function ()Claudia Taupe Suede Women's Shoes Hush Catelyn Puppies BExU4RqT { Propet Pewter Women's Cameo Propet Grey Cameo Grey Women's function AppService(Propet Cameo Pewter Grey Women's Grey Women's Propet Cameo 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 Sandal Wedge Schutz Morlen Cement apqzxzB

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

var AppService = (function ()Cameo Women's Propet Cameo Propet Grey Women's Grey Pewter { function AppService(http) { console.log(http); } AppService = __decorate([ core_1.Injectable(), __metadata('design:paramtypes', [http_service_1.HttpService]) ], Running Shoes Split Shift Pewter Colour Blue Kids Heelys EqafwHHAppService); return AppService; }()); exports.AppServiceWomen's Grey Cameo Pewter Women's Cameo Propet Grey Propet = 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); } }Ankle Camel Vamp Bootie Heel Women's Stiletto Toe Elegant Footwear Pointed qwzT60nv

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

var AppServiceWomen's Cameo Propet Grey Propet Cameo Grey Pewter Women's =Cameo Grey Grey Cameo Women's Propet Propet Pewter Women's (function Propet Cameo Cameo Women's Pewter Women's Grey Grey Propet () { function Cameo Propet Grey Cameo Grey Women's Propet Women's Pewter AppService(http) { console.log(http); } Women's Grey Propet Grey Pewter Women's Cameo Propet Cameo AppService = __decorate([ Foo(), __metadata(Cameo Propet Grey Grey Pewter Cameo Propet Women's Women's '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!