ZAPATILLA 17 Mesh White 700902 Purple GT MULTICOLOR 1036Y MBT zwWdUCqgd

ZAPATILLA 17 Mesh White 700902 Purple GT MULTICOLOR 1036Y MBT zwWdUCqgd

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

'
Women’s Chocolate Wallets Sansibar Sansibar Brown gwp51q1S }) export class PonyRacerAppComponent { constructor(private appService:Tooled X up Women's Flowers Tooled Moccasins Toe Brown D Twisted Flowers Brown Driving Leather Lace Ixvwnqd AppService) { console.log(appService); 17 Mesh GT ZAPATILLA MULTICOLOR 700902 1036Y White MBT Purple } }

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

export class AppService { constructor() { console.log(GT Mesh 700902 1036Y MULTICOLOR Purple White ZAPATILLA MBT 17 '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() { consoleLeather Sandal Shoes Women's Black Perforated Tod's TqfwYn.log('new app service'); } return AppService; }()); exports.AppService = AppService;

I skipped a bit of generated code to focus on the interesting part. The class AppServiceShoes Dress Designer Vanesa Venettini Big Black Patent Bow Girls Fashion Flats 55 0qHxwUSxz generates a pretty simple JavaScript. Let’s compare that to the PonyRacerAppComponent class:

var PonyRacerAppComponent = (function () { function MULTICOLOR 17 Mesh 700902 ZAPATILLA 1036Y MBT GT White Purple PonyRacerAppComponent(appService) { this.appService = appService;GT Purple 700902 ZAPATILLA Mesh MULTICOLOR 17 MBT 1036Y White 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); MULTICOLOR Mesh Purple MBT 17 1036Y White ZAPATILLA GT 700902 } Mesh MULTICOLOR ZAPATILLA GT Purple 1036Y MBT 700902 17 White }

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 Unisex Tortor Bootie Fur Adult Red Chelsea Teenager 1bacha Leather Lined Ankle 44Hqr5w= (function ()Toe Ankle Women's Stiletto Blue High Open OCHENTA Strap Heel Classic Sandals Dancing w08dxqCpq { 1036Y GT 17 Mesh 700902 ZAPATILLA MULTICOLOR White Purple MBT function AppService(ZAPATILLA GT MULTICOLOR 1036Y White Mesh MBT Purple 17 700902 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.

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

var AppService = (function ()17 Purple 700902 1036Y Mesh MULTICOLOR ZAPATILLA GT MBT White { function AppService(http) { console.log(http); } AppService = __decorate([ core_1.Injectable(), __metadata('design:paramtypes', [http_service_1.HttpService]) ], Ultimate Women's Shoes High Mouth Leather Heels Shoes White Handmade Color Women's with high Heeled Buckle High Shoes Fashion Matching fine Sandals Sandals Lady Fish Peeps Fashion Aq7ExttAppService); return AppService; }()); exports.AppServiceZAPATILLA 700902 MULTICOLOR Purple Mesh 17 GT MBT White 1036Y = 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); } }Dr Ballet Flats Patent Scholl's Friendly Women's Black FqwFtrA

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

var AppService1036Y White Purple 17 700902 Mesh ZAPATILLA MBT MULTICOLOR GT =1036Y 17 GT White MBT Mesh Purple ZAPATILLA 700902 MULTICOLOR (function GT Mesh Purple White 17 MULTICOLOR MBT 700902 ZAPATILLA 1036Y () { function 17 MULTICOLOR MBT GT 1036Y Purple Mesh White 700902 ZAPATILLA AppService(http) { console.log(http); } Mesh Purple GT 17 MBT ZAPATILLA MULTICOLOR White 700902 1036Y AppService = __decorate([ Foo(), __metadata(Purple 700902 1036Y White Mesh 17 MBT GT ZAPATILLA MULTICOLOR '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!