Deep copy of Angular Reactive Form?

This is how I would do it:

copyFormControl(control: AbstractControl) {
    if (control instanceof FormControl) {
        return new FormControl(control.value);
    } else if (control instanceof FormGroup) {
        const copy = new FormGroup({});
        Object.keys(control.controls).forEach(key => {
            copy.addControl(key, copyFormControl(control.controls[key]));
        });
        return copy;
    } else if (control instanceof FormArray) {
        const copy = new FormArray([]);
        control.controls.forEach(control => {
            copy.push(copyFormControl(control));
        })
        return copy;
    }
}

I personally use lodash cloneDeep() function found here:

https://lodash.com/docs/#cloneDeep

I use it this way:

const newFormGroup: any = _.cloneDeep(myFormGroup);

And you if you want it strongly typed, you can add as FormGroup as @Andre Elrico suggested in the comments:

const newFormGroup = _.cloneDeep(myFormGroup) as FormGroup;

This is the deep copy function I came up with which also retains the associated validator / async validator functions and disabled status of each AbstractControl.

/**
 * Deep clones the given AbstractControl, preserving values, validators, async validators, and disabled status.
 * @param control AbstractControl
 * @returns AbstractControl
 */
export function cloneAbstractControl<T extends AbstractControl>(control: T): T {
  let newControl: T;

  if (control instanceof FormGroup) {
    const formGroup = new FormGroup({}, control.validator, control.asyncValidator);
    const controls = control.controls;

    Object.keys(controls).forEach(key => {
      formGroup.addControl(key, cloneAbstractControl(controls[key]));
    })

    newControl = formGroup as any;
  }
  else if (control instanceof FormArray) {
    const formArray = new FormArray([], control.validator, control.asyncValidator);

    control.controls.forEach(formControl => formArray.push(cloneAbstractControl(formControl)))

    newControl = formArray as any;
  }
  else if (control instanceof FormControl) {
    newControl = new FormControl(control.value, control.validator, control.asyncValidator) as any;
  }
  else {
    throw new Error('Error: unexpected control value');
  }

  if (control.disabled) newControl.disable({emitEvent: false});

  return newControl;
}