angular - Angular2: Property 'controls' does not exist on type 'AbstractControl'. Error when accessing .control of an object within a formarray thru an index

Question

I'm trying to push another formbuilder within a formarray but it gives me an error since I think there are no items in the array when initializing the code, hence there are no controls. The error is Property 'controls' does not exist on type 'AbstractControl' after the

(<FormArray>this.loanTypeForm.controls['frequency']).controls[index]

I'm using angular 2.0.0-beta.17

let settingsForm: FormArray = new FormArray([]);
      (<FormArray>this.loanTypeForm.controls['frequency']).push(
        this.formBuilder.group({
          'name': [value, Validators.required],
          'settings': settingsForm,
        })
      );
(<FormArray>this.loanTypeForm.controls['frequency']).controls[index].controls['settings'].push(
      this.formBuilder.group({
        'term': [null, Validators.required],
        'eir': [null, Validators.required],
      })
    );

Answer 1

You can use ['controls'] instead of .controls, as below:

(<FormArray>this.loanTypeForm.controls['frequency']).controls[index]['controls']['settings'].push(...)

But in order to simplify and provide more readability I'd suggest you to change it all to:

const control = this.loanTypeForm.get(`frequency.${index}.settings`) as FormArray;
control.push(...);