Find out if object is instance of ember mixin (has property of it)

I have an Ember object which has multiple properties of which some are Ember objects themselves. I need to recursively loop through this structure with a common method work() to these objects. Therefor I created an Ember mixin.

App.mix = Ember.Mixin.create({
  work: function () {
    for (var key in this) {
      if ( this[key].isMix() ) // !!!
        this[key].work();
      else
        /* do stuff */
    }
  }
});

App.obj = Ember.Object.extend(App.mix, {
  prop1: 'foo',
  prop2: 'bar',
  child: null
});

test = new App.obj;
test.child = new App.obj;
test.work();

The problem now is, that I need to determine inside the loop, which of the properties of a parent object is another Ember object. If I found one, I need to call .work() on it.

The question is, how to determine if a object is of the mixin, or has the property work.

Example for the issue: http://ift.tt/1NBwFlq