reactive2

reactiveform2.ts

form: FormGroup;

constructor(
  private fb: FormBuilder
) { }

ngOnInit() {
  this.form = this.fb.group({
    type: [1, Validators.required],
    house: ['',Validators.required],
    apartment: ['']
  });

  this.form.controls['type'].valueChanges.subscribe((newValue) => {
    const controls = this.form.controls;
    // Remove the house field validator and make the validator for apartment
    if(newValue.type !== 1) {
      controls['house'].setValidators(null);
      controls['house'].updateValueAndValidity(Validators.required);
    } else { // Opposite
      controls['apartment'].setValidators(null);
      controls['apartment'].updateValueAndValidity(Validators.required);
    }
  })
}