###Angular enables you to $watch anything:
- $scope.foo
$scope.$watch('foo', cb);
- var foo
$scope.getFoo = function() { return foo; }
$scope.$watch('getFoo', cb);
- multiple values
$scope.foo, $scope.bar
$scope.$watch('[foo, bar]', cb);
// or
$scope.$watch('{some: foo, thing: bar}');