Test

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
	checkItem: Ember.computed('items.firstObject.bar.[]', function () {
    return this.get('items.firstObject.bar.firstObject.test')
  }),
  nonCompute: null,
  actions: {
   doStuff() {
     console.log(this.get('items.firstObject.bar'))
     debugger
     this.set('nonCompute', this.get('items.firstObject.bar.firstObject.test'))
   }
  }
});

models.my-model.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';

export default Model.extend({
});

routes.application.js

import Ember from 'ember';
import DS from 'ember-data'
export default Ember.Route.extend({
  model() {

    return {}
  },
    setupController(controller, model) {
    // Call _super for default behavior
    this._super(controller, model);
    // Implement your custom setup after
    const promise1 = new Promise(function(resolve, reject) {
      setTimeout(resolve, 4000, [{test: '?'}]);
    })
    let promiseObject = DS.PromiseObject.create({
      promise: promise1
    });
    this.controllerFor('application').set('items', [{
    	bar: promiseObject
    }]);
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<h3> Question mark should appear: ( {{checkItem}} ), it does! </h3>
<br>
<button {{action "doStuff"}}>I work {{checkItem}}</button>
<br>
{{outlet}}
<br>
{{nonCompute}}
<br>
{{log items.firstObject.bar.firstObject}}

twiddle.json

{
  "version": "0.13.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}