Watching a controller's properties from a directive in Angular

Question

I'm trying to watch a controller's properties from it's associated directive from within the link function. The controller itself is set to the 'window' object on the $scope using controllerAs; here is the directive definition:

function windowDirective() {
  return {
    transclude: true,
    template: template,
    restrict: 'E',
    controller: WindowCtrl,
    controllerAs: 'window',
    link: function($scope, $element, $attrs, $ctrl) {
      $scope.$watch('window.x', function(newValue, oldValue) {
        // access x here
      });
    }
  };
}

And here is WindowCtrl

'use strict';
class WindowCtrl {
  move(x, y) {
    this.x = x;
    this.y = y;
  }
}

module.exports = WindowCtrl;

move(x, y) is being called when I drag on a child directive - it is definitely being called and this.x and this.y are definitely being set on WindowCtrl. In addition, if I console.dir the $scope then fire move() a few times, I can open up the scope in chrome (because it's lazily evaluated) and see that $scope.window.x and $scope.window.y are indeed being set.

However, my $scope.$watch never actually fires aside from when it initially detects that window.x is undefined. Not really sure how to proceed. I did search and try all of the solutions I found but none of them seemed to have worked.

I'm using Angular 1.3.16.

NB: The access to WindowCtrl.move() is only ever from within Angular's digest cycle - see below - however using $scope.$apply() solves this. I'm not sure why this is the case. Could you explain? The below is a directive which is nested inside of the above directive. It will invoke the method at onDrag , which in my example points to window.move(x, y);

function windowHeaderDirective() {
  return {
    transclude: true,
    template: template,
    replace: true,
    require: `^${windowDirective.$name}`,
    scope: {
      enableClose: '=actionClose',
      draggable: '=',
      onDrag: '&'
    },
    bindToController: true,
    link: function($scope, $element, $attrs, $ctrl) {
      $scope.close = $ctrl.close.bind($ctrl);
      let moving = false;
      $element.on('mousemove', function(event) {
        if(!moving) return
        const { x, y } = event;
        $scope.header.onDrag({ x, y });
        // $scope.$apply here will fix this issue, but why? Isn't $element.on within angular's digest cycle??
      });
      $element.on('mousedown', function(event) {
        moving = true;
      });
      $element.on('mouseup', function(event) {
        moving = false
      });
    },
    controller: controller,
    controllerAs: 'header'
  };
}

Answer 1

In the $watch try using a function watcher like this:

$scope.$watch(function() {
  return $scope.window.x
 }, ...

Answer 2

Self answer:

It appears, due to my update, I answered the question myself, so;

$element.on does not appear to actually be in the angular digest cycle - this is fairly surprising for me, I assumed it would be. However, this essentially means that my code works as it should - it's just the changes to the variables on the controller are not apparent straight away. The way to fix this is to simply use either ng-mousedown et al, or $scope.$apply in the $element.on handler.