import { FormGroup } from '@angular/forms'; @Component({ selector: 'my-component', template: 'MyComponent Template' }) export class MyComponent implements OnInit { nameChangeLog: string[] = []; heroForm: FormGroup; ngOnInit() { this.logNameChange(); } logNameChange() { const nameControl = this.heroForm.get('name'); nameControl.valueChanges.forEach( (value: string) => this.nameChangeLog.push(value) ); } }