Custom Validator

export class HomeComponent {
  userForm: FormGroup;

  constructor (formBuilder: FormBuilder) {
    this.userForm = formBuilder.group({
      name: ['', this.validateName ],
      email: '',
      address: formBuilder.group({
        country: '',
        city: '',
      })
    });
  }

  validateName(form) {
    return form.value.trim() !== '' ? null : {
      validateName : {
        errors: true
      }
    }
  }
}