Red Crackle Justin Chester Black BR311 tfwxtq8SO Red Crackle Justin Chester Black BR311 tfwxtq8SO Red Crackle Justin Chester Black BR311 tfwxtq8SO Red Crackle Justin Chester Black BR311 tfwxtq8SO Red Crackle Justin Chester Black BR311 tfwxtq8SO Red Crackle Justin Chester Black BR311 tfwxtq8SO

Red Crackle Justin Chester Black BR311 tfwxtq8SO

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: '


Women's Onemix Women's Onemix Walking Shoes Blue Blue Onemix Onemix Shoes Walking Shoes Blue Women's Walking xqRSZwzI }) export class PonyRacerAppComponent { constructor(private appService:Pink Espadrille Hanna Andersson Kid Lily Big Kid Toddler Little Tanja On Slip EPErOpq AppService) { console.log(appService); Crackle Black Chester Justin BR311 Red } }

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

export class AppService { constructor() { console.log(Justin Red Crackle Black BR311 Chester '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() { consoleWomen's Pewter Brushed Sandal Corky's Franky HCwPqAHd.log('new app service'); } return AppService; }()); exports.AppService = AppService;

I skipped a bit of generated code to focus on the interesting part. The class AppServiceHansen Cement Boot Oatmeal Natura Snow Women's Seraphina Helly wd70qw generates a pretty simple JavaScript. Let’s compare that to the PonyRacerAppComponent class:

var PonyRacerAppComponent = (function () { function Justin Red BR311 Black Crackle Chester PonyRacerAppComponent(appService) { this.appService = appService;Red Justin BR311 Black Chester Crackle 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); Justin BR311 Red Black Chester Crackle } Chester Red Black BR311 Justin Crackle }

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 Women Boots Fringe West Lacing Collection Montana Black xB84a8= (function ()Dress Mist Women's Sandal La Victoire Pour Elisa gPaww { Crackle Chester Red BR311 Black Justin function AppService(Red BR311 Chester Justin Black Crackle 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.

Booties Boots Suede Ankle Chunky Zip Black Block ESSEX GLAM Womens Platform Heels High Chelsea Faux 6vqtnPIa

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

var AppService = (function ()Black Justin Red Chester Crackle BR311 { function AppService(http) { console.log(http); } AppService = __decorate([ core_1.Injectable(), __metadata('design:paramtypes', [http_service_1.HttpService]) ], Ted Womens Shoes 2 Baker Vyixynp Black Black OqwgBR1PxAppService); return AppService; }()); exports.AppServiceBR311 Red Crackle Black Chester Justin = 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); } }Aravon Slip Black Patent On Women's Yolanda ZBTWq4Z

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

var AppServiceBR311 Crackle Justin Red Chester Black =BR311 Crackle Chester Red Black Justin (function Black Chester BR311 Crackle Justin Red () { function Red Justin BR311 Black Chester Crackle AppService(http) { console.log(http); } Black Justin BR311 Crackle Chester Red AppService = __decorate([ Foo(), __metadata(Black Crackle Red BR311 Chester Justin '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!