Angular Reactive Form Programmatic Setter

Question

I have an Angular Reactive Form with validation. What's the proper way to invoke the setter for my hiddenComposedField?

component.ts

ngOnInit() {
  this.myForm = this.formBuilder.group({
    'field1': ['', [Validators.required]],
    'field2': ['', [Validators.required]],
    'hiddenComposedField': [''],
  });

  this.myForm.get('field1').valueChanges.subscribe((val) => {
     this.setHiddenComposedField();
  });
  this.myForm.get('field2').valueChanges.subscribe((val) => {
     this.setHiddenComposedField();
  });
}

setHiddenComposedField() {
    let field1 = this.myForm.get('field1').value;
    let field2 = this.myForm.get('field2').value;

    // This doesn't work, but I want something like it:
    this.myForm.set('hiddenComposedField',field1 + ' ' + field2); // :(
}

component.html

<form [formGroup]="myForm">
  <input formControlName="field1">
  <input formControlName="field2">
  <!-- NB: hiddenComposedField is not exposed to the user; -->
  <!--     it is only on the submitted form model. -->
  <button type="submit">Submit</button>
</form>

Answer 1

Something like this should work so that you are getting the Control first and then setting its value.

this.myForm.get('hiddenComposedField').setValue(field1 + ' ' + field2);