experiment-computed-properties

controllers.application.js

import Ember from 'ember';
const { computed } = Ember;

let x = 0;

export default Ember.Controller.extend({
//  x: computed(() => (Ember.Object.create({ a: [], b: []}))),
  x: computed(() => ({ a: [], b: []})),
  y: 'hi',
  hello: computed('y', 'x.a.[]', 'x.b.[]', function() {
    console.log('hi')
    console.log(this.get('x.a'));
    return this.get('y') + this.get('x.a.lastObject') + this.get('x.b.lastObject');
  }),
  actions: {
    do() {
      this.get('x.a').pushObject(x++);
      this.get('x.b').pushObject(x++);
    },
  }
});

templates.application.hbs

{{hello}}
<button onclick={{action "do"}}>do</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"
  }
}