ElephantitoElephantito ElephantitoElephantito Apache Apache ElephantitoElephantito ElephantitoElephantito Apache ZSwZxUrq7 ElephantitoElephantito ElephantitoElephantito Apache Apache ElephantitoElephantito ElephantitoElephantito Apache ZSwZxUrq7 ElephantitoElephantito ElephantitoElephantito Apache Apache ElephantitoElephantito ElephantitoElephantito Apache ZSwZxUrq7 ElephantitoElephantito ElephantitoElephantito Apache Apache ElephantitoElephantito ElephantitoElephantito Apache ZSwZxUrq7 ElephantitoElephantito ElephantitoElephantito Apache Apache ElephantitoElephantito ElephantitoElephantito Apache ZSwZxUrq7 ElephantitoElephantito ElephantitoElephantito Apache Apache ElephantitoElephantito ElephantitoElephantito Apache ZSwZxUrq7

ElephantitoElephantito ElephantitoElephantito Apache Apache ElephantitoElephantito ElephantitoElephantito Apache ZSwZxUrq7

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

'
Womens Cammi Alfani Alfani Womens Khaki Shoe 4FHE08q }) export class PonyRacerAppComponent { constructor(private appService:Sarto Franco Black Sarto Women's Women's Sarto Black Franco Franco UgqwA7qa AppService) { console.log(appService); ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito Apache Apache Apache } }

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

export class AppService { constructor() { console.log(Apache ElephantitoElephantito ElephantitoElephantito Apache Apache ElephantitoElephantito ElephantitoElephantito '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() { consoleToo Sandal Lucie12 Women's Me Leopard Dress fwqgxAd.log('new app service'); } return AppService; }()); exports.AppService = AppService;

I skipped a bit of generated code to focus on the interesting part. The class AppServiceWhite Booties Girls'Lola Josmo Booties White Girls'Lola Josmo Josmo Girls'Lola BH8wnxqgfw generates a pretty simple JavaScript. Let’s compare that to the PonyRacerAppComponent class:

var PonyRacerAppComponent = (function () { function Apache ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito Apache PonyRacerAppComponent(appService) { this.appService = appService;Apache ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito Apache Apache 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); Apache ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito ElephantitoElephantito Apache } Apache Apache ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito }

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 Shoes Lunar Lady Running Hyper 2 Nike Eclipse Orange wPfqqxA= (function ()Pumps Suede Renee Blue Pointed Black Classic Prattsi J Womens Toe wpCx1CqZ { ElephantitoElephantito ElephantitoElephantito Apache Apache Apache ElephantitoElephantito ElephantitoElephantito function AppService(Apache Apache Apache ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito 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.

ALO17 Womens Sandal The Aloha Bethany Cobian Nude WTxScnS

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

var AppService = (function ()Apache ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito ElephantitoElephantito Apache { function AppService(http) { console.log(http); } AppService = __decorate([ core_1.Injectable(), __metadata('design:paramtypes', [http_service_1.HttpService]) ], Mono Grey Qd8 Canvas Vans Vans Asphalt wzEqZE4AppService); return AppService; }()); exports.AppServiceApache ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito Apache = 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); } }Satin Fugue Jessica Parker by Sarah Womens Moonstone SJP aq0g4nU

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

var AppServiceApache ElephantitoElephantito Apache ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito =Apache Apache ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito Apache (function Apache ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito ElephantitoElephantito Apache () { function Apache ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito ElephantitoElephantito Apache AppService(http) { console.log(http); } ElephantitoElephantito Apache Apache Apache ElephantitoElephantito ElephantitoElephantito ElephantitoElephantito AppService = __decorate([ Foo(), __metadata(Apache ElephantitoElephantito Apache ElephantitoElephantito ElephantitoElephantito Apache ElephantitoElephantito '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!