valueChanges.ts

@Component({
  selector: 'my-component',
  template: `
    <input [formControl]="control">
    <button (click)="toggleEnabledState()">Toggle State</button>
  `,
})
export class MyComponent implements OnInit {
  control = new FormControl('Default Value');

  ngOnInit() {
    this.control.valueChanges.subscribe(console.log);
  }

  toggleEnabledState() {
    this.control.enabled ? this.control.disable() : this.control.enable();
  }
}