title: Get name of Form Control
body: <p>I'm working with reactive forms in angular, I need to compare the start date "start date" with the end date "end date", both controls are validated in the "dateLessThan" function, but the problem is that I do not know how to ask for control is evaluating</p>
  
  <pre><code>//Some stuff
  public fechaInicio = new FormControl('', [
      Validators.required    
      , this.dateLessThanTo
  
  ]);
  public fechaFin = new FormControl('', [
      Validators.required     
      , this.dateLessThan
  ]);
  
  
  
   createForm() {
      this.contratoForm = this.formBuilder.group({    
          fechas: this.formBuilder.group({
              fechaInicio: this.fechaInicio,
              fechaFin: this.fechaFin
          }, { validator: this.dateLessThan('fechaInicio', 'fechaFin') }),          
  
      });
  }
  </code></pre>
  
  <p>Here I Need to know the name of control for compare dates:</p>
  
  <pre><code> dateLessThanTo(fieldControl: FormControl) {
      //
      //if (fechaInicio.value &gt; FechaFin.value){
      //      return true;
      //}
      //else{
      //  return false;
      //  }
  
  }
  
  //Some stuff
  </code></pre>