myForm: FormGroup;
  myPassword = new FormControl();

  constructor(dataService: DataService) {

    this.myForm = new FormGroup(
      {
        myUserName: new FormControl('', [Validators.required]),
        myPassword: this.myPassword
      }
    );
  }

  reactiveLogin(){
    console.log(JSON.stringify(this.myForm.value));
  }