angular - 속성 값에 따라 클래스를 사용

[ngClass]  클래스의 속성을 기반으로 CSS 클래스를 선택하려고하면 작동하지 않습니다.

즉,

[ngClass]="{'alert alert-danger': employeeForm.get('fullname').errors && (employeeForm.get('fullname').touched || employeeForm.get('fullname').dirty) }"

저는 YouTube 자습서

export class CreateEmployeeComponent implements OnInit {
  employeeForm: FormGroup;
  constructor(private fb: FormBuilder) { }
  ngOnInit() {
    this.employeeForm = this.fb.group({
      fullname: ['', Validators.required ],
      email: [''],
      skills : this.fb.group({
        skillName: [''],
        experience: [''],
        proficiency: ['beginner']
      })
    });
  }
  onLoadDataClick(): void {
    this.employeeForm.setValue({
      fullname: 'Jamshaid Tariq',
      email: 'jamshaid055@yahoo.com',
      skills: {
        skillName: 'C#',
        experience: 1,
        proficiency: 'beginner'
      }
    });
  }
  onSubmit(): void {
    console.log(this.employeeForm.value);
  }
}