How to know which field has fired cross-validation in FormGroup Validator

Question

My answer is about cross field validation in Angular Form (check the documentation here cross-field-validation). I would like to know how to find which field's change has fired the form validator when I am inside the validator function (checkAnno, in the example below). This is my code

ngOnInit() {
this.elaborazioneForm = new FormGroup({
  anno: new FormControl('',[Validators.required]),
  modello: new FormControl('',[Validators.required]),
  tipo: new FormControl('', [Validators.required]),
  nProtocollo: new FormControl({ value: null, disabled: true })
},
  {validators: this.checkAnno()}
);
}


checkAnno(): ValidatorFn {
return (formGroup: FormGroup) => {
  if (
    !!formGroup.get('anno').value &&
    !!formGroup.get('modello').value &&
    Math.abs(parseInt(formGroup.get('modello').value, 10) - parseInt(formGroup.get('anno').value, 10)) >= 2
  ) {

here I would like to know which is the control that, with its change, has activated the validation of the form

    formGroup.controls['anno'].setErrors({twoYearsOrMore: true});
    formGroup.controls['modello'].setErrors({twoYearsOrMore: true});
    return { twoYearsOrMore: true };
  } else {
    formGroup.controls['anno'].setErrors(null);
    formGroup.controls['modello'].setErrors(null);
    return null;
  }
};

}

Do you have any ideas how to reach the goal?

Answer 1

If you want to know how to check which field is valid or invalid you can use this

this.form.get('field').invalid

Or this for valid

this.form.get('field').valid

It will work too

this.form.controls.field.invalid