How to get name of input field from Angular2 FormControl object?

Question

I have an Angular 2 application that uses the ReactiveForms module to manage a form that uses a custom validator. The validator receives a FormControl object. I have a few input fields that could use the same custom validator if only I knew the name of the field when the FormControl was passed to the validator.

I can't find any method or public property on FormControl that exposes the input field's name. It's simple enough to see its value, of course. The following shows how I would like to use it:

public asyncValidator(control: FormControl): {[key: string]: any} {
  var theFieldName = control.someMethodOfGettingTheName(); // this is the missing piece

  return new Promise(resolve => {
      this.myService.getValidation(theFieldName, control.value)
        .subscribe(
          data => {
            console.log('Validation success:', data);
            resolve(null);
          },
          err => {
            console.log('Validation failure:', err);
            resolve(err._body);
          });
    });
  }

Answer 1

To expand on Radim Köhler answer. here is a shorter way of writing that function.

getControlName(c: AbstractControl): string | null {
    const formGroup = c.parent.controls;
    return Object.keys(formGroup).find(name => c === formGroup[name]) || null;
}