Lazy Load External JavaScript Library in Angular

quill-editor.component.ts

declare var Quill: any;

@Component({
  //...
})
export class QuillEditorComponent implements OnInit {

  constructor(
    // ...
    private readonly svc: QuillEditorService,
    @Inject(DOCUMENT) private readonly document: any
  ) {}

  ngOnInit() {
    this.svc.lazyLoadQuill().subscribe(_ => {
      if (!Quill) {
        Quill = this.document.defaultView.Quill;
      }
      this.setupQuill();
    });
  }

  setupQuill() {
    if (!Quill) {
      return;
    }
    // set up External JS library
  }
}