Angular 12 References/ Core
🍀 Angular References


A constructor parameter decorator that tells the DI framework to retrieve a dependency from any injector until reaching the host element of the current component.

constructor(@Host() service: Service) {}


class OtherService {}
class HostService {}
@Directive({selector: 'child-directive'})
class ChildDirective {
  logs: string[] = [];
  constructor(@Optional() @Host() os: OtherService, @Optional() @Host() hs: HostService) {
    // os is null: true
    this.logs.push(`os is null: ${os === null}`);
    // hs is an instance of HostService: true
    this.logs.push(`hs is an instance of HostService: ${hs instanceof HostService}`);
  selector: 'parent-cmp',
  viewProviders: [HostService],
  template: '<child-directive></child-directive>',
class ParentCmp {
  selector: 'app',
  viewProviders: [OtherService],
  template: '<parent-cmp></parent-cmp>',
class App {