Need to watch keys

controllers.application.js

import Ember from 'ember';


export default Ember.Controller.extend({
	init() {
    this._super(...arguments);
    
    this.set('foo', {count: 0});
  },
	justFoo: Ember.computed('foo', function() {
  	return this.get('foo.count');
  }),
  fooChild: Ember.computed('foo.count', function() {
  	return this.get('foo.count');
  }),
  actions: {
  	incr() {
      this.set('foo.count', this.get('foo.count') + 1);
    },
  }
});

templates.application.hbs

<div>justFoo: {{justFoo}}</div>
<div>fooChild: {{fooChild}}</div>

<button {{action 'incr'}}>click me</button>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}