http://stackoverflow.com/questions/40027716/why-doesnt-the-handlebars-if-helper-call-the-actual-model-computed-property

controllers.application.js

import Ember from 'ember';

var item = Ember.Object.extend({    
});
item.reopen({
  isAddedToCart: function () {
        console.log('addedToCart method has been called');
        return false;
    }.property()
});
export default Ember.Controller.extend({
  appName: 'Ember Twiddle ',
  itemObj : item.create(),
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
{{log itemObj}}
{{itemObj.isAddedToCart}}
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "1.12.2",
    "ember-data": "2.8.0",
    "ember-template-compiler": "1.12.2",
    "ember-testing": "1.12.2"
  },
  "addons": {}
}