Easy concepts of Angular 2.x +

To learn AngularJS 2.x + learn the below concepts decorators and typescript classes.

Module Decorator

@NgModule({
  declarations: [
    AppComponent, TestComponent
  ],
  imports: [
    BrowserModule, HeaderModule, RoutingModule,
  ],
  exports: [],
  providers: [UserService],
  bootstrap: [AppComponent]
})

Component Decorator

@Component({
  selector: 'app-blog',
  templateUrl: './blog.component.html',
  styleUrls: ['./blog.component.css'],
  providers: [HttpService],
})

Pipe Decorator

@Pipe({
  name: 'safeHtml'
})

Directive Decorator

@Directive({
  selector: '[tagDirective]'
})

Above all are the Decorators of angularJS to decorate the typescript class into angular module,component,pipe,directive etc. The classes who has decorators need to be declared in the declarations part of @ngModule and those who have not decorators only typescript casses need to be put in the providers of @ngModule (global all over module) or @Component Decorators.

You cannot declare single decorator like component,pipe etc. in multiple modules for this you need to make a shared module and export the decorators in the shared module and import the shared modules on other modules.