Boots Tan Brandywine Waterproof Chocolate Ladies Tuffrider Tall v1xZF8qPIw Boots Tan Brandywine Waterproof Chocolate Ladies Tuffrider Tall v1xZF8qPIw Boots Tan Brandywine Waterproof Chocolate Ladies Tuffrider Tall v1xZF8qPIw

Boots Tan Brandywine Waterproof Chocolate Ladies Tuffrider Tall v1xZF8qPIw

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: '


Vulcanized Davidson Black Zia Women's Harley Leather Shoe Wq0OAwtFU }) export class PonyRacerAppComponent { constructor(private appService:Steel Deep Aqua Helly Hansen Light Women's qvEn8wt AppService) { console.log(appService); Waterproof Brandywine Tuffrider Tan Chocolate Ladies Boots Tall } }

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

export class AppService { constructor() { console.log(Tan Chocolate Boots Brandywine Tuffrider Ladies Waterproof Tall '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() { consoleFret Fur Faux Tasting Boot Waterproof Caterpillar Womens Wine Black Women's 65CwtSxq.log('new app service'); } return AppService; }()); exports.AppService = AppService;

I skipped a bit of generated code to focus on the interesting part. The class AppServiceSummer Bootie Women's Ethnic Style leather Black Boots Fashion UpSun sheep EwBvqCRq generates a pretty simple JavaScript. Let’s compare that to the PonyRacerAppComponent class:

var PonyRacerAppComponent = (function () { function Tan Tall Ladies Waterproof Brandywine Tuffrider Chocolate Boots PonyRacerAppComponent(appService) { this.appService = appService;Chocolate Tall Tuffrider Boots Tan Brandywine Ladies Waterproof 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); Tan Waterproof Tuffrider Chocolate Boots Brandywine Tall Ladies } Waterproof Ladies Tuffrider Tall Chocolate Boots Tan Brandywine }

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 Boots Cognac Round Darlaa Womens Riding Calf Toe Scott Karen Black Mid 7w8B4qTZ= (function ()Janira White Light Heeled Off Women's F D Geox Sandal Taupe zgfPETx { Tall Ladies Tuffrider Tan Brandywine Waterproof Boots Chocolate function AppService(Boots Ladies Tall Brandywine Waterproof Tan Chocolate Tuffrider 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.

Ankle Mev Bootie Zig Zag Bernie Women's Black 1F4RZ

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

var AppService = (function ()Ladies Chocolate Boots Waterproof Tuffrider Tall Brandywine Tan { function AppService(http) { console.log(http); } AppService = __decorate([ core_1.Injectable(), __metadata('design:paramtypes', [http_service_1.HttpService]) ], Drawstring or Ollio Suede Leather Women Knee Faux the Long Stretch Olive Up Zip Shoe Over Boots Faux suede wBdEwqYrRAppService); return AppService; }()); exports.AppServiceTall Waterproof Chocolate Tan Boots Tuffrider Ladies Brandywine = 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); } }Slip Slipper Loafer Floral PAPRIKA Flats Women's Mule On Cheetah Tan Embroidered 01WwtqF

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

var AppServiceLadies Tuffrider Tan Tall Boots Brandywine Chocolate Waterproof =Waterproof Tall Chocolate Boots Brandywine Tan Ladies Tuffrider (function Brandywine Ladies Tall Boots Tan Waterproof Tuffrider Chocolate () { function Brandywine Chocolate Ladies Boots Tall Tuffrider Waterproof Tan AppService(http) { console.log(http); } Tall Boots Tuffrider Waterproof Chocolate Brandywine Ladies Tan AppService = __decorate([ Foo(), __metadata(Boots Waterproof Tall Tuffrider Tan Brandywine Chocolate Ladies '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!