Angular: how to extend a controller without using $ scope?

if you want to use the controller in the recommended "controller" how is the way?

lets skip this part where extending a controller is bad practice, I still believe there are cases where it is reasonable and useful.

Wrestled with controller extension in angularjs for a while, came up with the same as here: Angular: Controller extension which I like best. we still have the parent as an angularjs regulator, which makes sense in inheriting the controller, i.e. it is not a service with a $ scope field, which is not a prototype, which most likely is not testable, it is not a simple js function / object - this is an angular controller we want to extend in angularjs controllers.

now the problem with this solution is one: what if we want to use it in the recommended "controller as" path without $ scope visibility? I couldn't find anything with this on the internet, tried to make my own:

// @ngInject
function ParentCtrl(Service, CommonService) {
  var vm = this;

  //...

  // could be moved out to abstract extendable
  vm.extendTo = function(child) {
    // we need this reassignment to new vm reference,
    // to use overriden/child members in common/parent methods.
    vm = angular.extend(child, vm);
    return vm;
  };
}
angular.module('common').controller('ParentCtrl', ParentCtrl);

// @ngInject
function ChildCtrl($controller, SpecificService) {
  var vm = $controller('ParentCtrl', {Service: SpecificService}).extendTo(this);
}
angular.module('child').controller('ChildCtrl', ChildCtrl);
      

        
        
        
      

    

please, I need your opinions on the possible pitfalls of this solution, suggestions on how to do it better, in alternative ways. thank.