When your developing an angular 2/ionic 2 application and you get the the following error:

EXCEPTION: Error: Uncaught (in promise): EXCEPTION: Error in :0:0
ORIGINAL EXCEPTION: No provider for UserService!
ORIGINAL STACKTRACE:
Error: DI Exception
    at NoProviderError.BaseException [as constructor] (http://localhost:8100/build/js/app.bundle.js:2300:23)
    at NoProviderError.AbstractProviderError [as constructor] (http://localhost:8100/build/js/app.bundle.js:27491:16)
    at new NoProviderError (http://localhost:8100/build/js/app.bundle.js:27528:16)
    at ReflectiveInjector_._throwOrNull (http://localhost:8100/build/js/app.bundle.js:28516:19)
    at ReflectiveInjector_._getByKeyDefault (http://localhost:8100/build/js/app.bundle.js:28544:25)
    at ReflectiveInjector_._getByKey (http://localhost:8100/build/js/app.bundle.js:28507:25)
    at ReflectiveInjector_.get (http://localhost:8100/build/js/app.bundle.js:28316:21)
    at ElementInjector.get (http://localhost:8100/build/js/app.bundle.js:29890:48)
    at ElementInjector.get (http://localhost:8100/build/js/app.bundle.js:29890:48)
    at ReflectiveInjector_._getByKeyDefault (http://localhost:8100/build/js/app.bundle.js:28541:24)
ERROR CONTEXT:
[object Object]

Your module exists, it’s setup and your import is working. So what’s up? You need to make it available for your application. In your app.ts you have 2 approach’s add a new paramter to your @Component called providers that takes an array of modules.

Angular 2 (non-Ionic)

@Component({ 
  templateUrl: “build/app.html”,
  providers: [UserService],
})

For Ionic you can also just pass it into the ionicBootstrap function, the second parameter to that is an array of modules:

ionicBootstrap(ConnectApp, [UserService]);

Hope this helps!