mapsuscirber,如何访问组件变量?

我有一个表单,我用一个脚本控制更改:

<form #f="ngForm">

  <mat-card-content>

    <mat-input-container>
      <input matInput [(ngModel)]="id" name="id" placeholder="id" (ngModelChange)="elementChanged$.next($event)"/>
      </mat-input-container>
   </mat-card-content>

</form>
export class myComponent implements OnInit {

 dataToGet: string;
 formChanged$: Observable<boolean>;
 elementChanged$: Subject<any> = new Subject<any>();
 elementSubscription: Subscription;

 constructor() {

   this.elementSubscription = this.elementChanged$  
     .debounceTime(500)
     .map(this.formHaveChanged)
     .subscribe(haveChanged => this.formChanged$ = haveChanged)
  }

  formHaveChanged(): Observable<boolean> {
    this.dataToGet -> fails because of this is mapSuscriber
    return Observable.of(true)
  }
}

所以我的问题很清楚,当我在formHaveChanged()函数“this”是MapsScriber而不是myComponent中时,我需要访问myComponent变量,但我无法获得它,我如何才能做到?