How to get formControlName Programmatically in Angular 5 or above

You can use that approach:

<input formControlName="item_name" #itemName (change)="inputChanged($event)">

When the input's value changes, the change event occurs, and Angular provides a corresponding DOM event object in the $event variable which this code passes as a parameter to the component's inputChanged() method.

inputChanged (event: any) { // without type info
this.myValue = event.target.value;
  }
}

Reference link: https://angular.io/guide/user-input

Another alternative more elegant:

template

<form [formGroup]="usersForm">
  <input type="text" formControlName="name" placeholder="name"/>
</form>

component class

export class AppComponent implements OnInit, OnDestroy {
  usersForm: FormGroup;
  message: string;

  private subscriptions$ = new Subscription();

  constructor( private formBuilder: FormBuilder) {}

  ngOnInit(): void {
    this.usersForm = this.formBuilder.group({
      name: '',
      age: '',
      gender: '',
    });

    this.subscriptions$.add(this.name.valueChanges.subscribe(value => {
      // Do someting
    }));
  }

  ngOnDestroy(): void {
    this.subscriptions$.unsubscribe();
  }

  get name(): AbstractControl {
    return this.usersForm.get('name');
  }
}

See the complete example in the Stackbliz:
https://stackblitz.com/edit/form-builder-example

Most straighforward way I've found:

HTML:

<input formControlName="item_name" (input)="inputChanged($event)">

TS:

inputChanged(e) {
  log(e.target.getAttribute('formControlName')) // item_name 
}

No need to add an id in every input. Just pass $event as parameter.

from this input field to get formControlName

<input formControlName="item_name" #itemName (input)="inputChanged(itemName)">

You only need to get the attribute formControlName

inputChanged(element: HTMLElement) {
  log(element.getAttribute('formControlName')) // item_name 
}