Angular Form

constructor(
    public navCtrl: NavController,
    public viewCtrl: ViewController,
    public navParams: NavParams,
    public formBuilder: FormBuilder
  ) {
    this.signupForm = this.formBuilder.group({
      username:
        ['',
          Validators.compose([
            Validators.required,
            Validators.minLength(4),
            Validators.pattern(/^[a-zA-Z_\-]+$/)
          ])
        ],
      password:
        ['',
          Validators.compose([
            Validators.required,
            Validators.minLength(4),
          ])
        ]
    });
  }