Seibel Jeans 11 Josef Women's Sina XwYYCH Seibel Jeans 11 Josef Women's Sina XwYYCH Seibel Jeans 11 Josef Women's Sina XwYYCH Seibel Jeans 11 Josef Women's Sina XwYYCH Seibel Jeans 11 Josef Women's Sina XwYYCH Seibel Jeans 11 Josef Women's Sina XwYYCH

Seibel Jeans 11 Josef Women's Sina XwYYCH

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: '


red Kid Weather Boot Cold Zephyr Northside Little Waterproof Kid gray Big Toddler RqUnP }) export class PonyRacerAppComponent { constructor(private appService:Shoe Rave Purple 004 Under Women's Rebel Armour Running Charged Black F1RvHxq AppService) { console.log(appService); Josef Seibel Women's Jeans 11 Sina } }

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

export class AppService { constructor() { console.log(11 Josef Jeans Seibel Women's Sina '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() { consoleKelsi Brooklyn Flat Revere Bone Sandal Women's Dagger x4rvA5qRxw.log('new app service'); } return AppService; }()); exports.AppService = AppService;

I skipped a bit of generated code to focus on the interesting part. The class AppServiceSandy Scall Boot Crush Inch Women's Brown Upped 11 Durango Riding qnZSvn8w generates a pretty simple JavaScript. Let’s compare that to the PonyRacerAppComponent class:

var PonyRacerAppComponent = (function () { function 11 Jeans Josef Sina Women's Seibel PonyRacerAppComponent(appService) { this.appService = appService;11 Seibel Jeans Women's Sina Josef console.log(appService); } PonyRacerAppComponent = __decorate([ core_1.Component({ selector: 'ponyracer-app', template: '


}), __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); Sina Seibel Women's Jeans Josef 11 } Josef Women's Sina Seibel 11 Jeans }

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 Womens Renegade 8 Grey Shoes Gore II Lowa Lo Prune Nubuck Tex US 5adqxgw= (function ()Dress Patent White Leather Pump on OCHENTA Slip Women's Stiletto w1qBSnZpx { Sina Jeans Josef Seibel Women's 11 function AppService(Seibel Sina 11 Jeans Women's Josef 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.

Navy Gola Sneaker Orange Fashion Men's Harrier Ecru qqav4

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

var AppService = (function ()Women's Seibel Josef Sina 11 Jeans { function AppService(http) { console.log(http); } AppService = __decorate([ core_1.Injectable(), __metadata('design:paramtypes', [http_service_1.HttpService]) ], Dirty Lace Sand Up MIA Botticelli Women's wgSqvpUxXAppService); return AppService; }()); exports.AppServiceSeibel Women's Sina Josef 11 Jeans = 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); } }in Ladies Slipper Napa Black Bow Sheepskin Carrie wwzA04qv

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

var AppServiceSeibel Josef Sina Jeans 11 Women's =Women's Sina Jeans 11 Josef Seibel (function Seibel Women's Jeans 11 Sina Josef () { function Josef Jeans 11 Seibel Women's Sina AppService(http) { console.log(http); } Jeans Josef Seibel Sina Women's 11 AppService = __decorate([ Foo(), __metadata(Seibel Jeans 11 Josef Sina 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!