New Twiddle

controllers.application.js

import Ember from 'ember';
import { getBy } from 'ember-awesome-macros';

export default Ember.Controller.extend({
	obj: Ember.Object.create({
    foo: 42
  }),
  prop: 'foo',
  value: getBy('obj', 'prop'),
  
  actions: {
    changed: function(value) {
      const before = this.get('value');
      this.set('obj.foo', value);
      const after = this.get('value');
      console.log(`before: ${before}, after: ${after}`)
    }
  }
});

templates.application.hbs

obj.foo: {{obj.foo}} <br>
value: {{value}} <br>
<input oninput={{action 'changed' value="target.value"}}>

twiddle.json

{
  "version": "0.13.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"    
  },
  "addons": {
    "ember-data": "2.16.3",
    "ember-awesome-macros": "0.41.0",
    "ember-macro-helpers": "0.17.0"
  }
}