TestOverride

controllers.application.js

import Ember from 'ember';

const PersonArray = Ember.Object.extend({
  shoppingList: ['eggs', 'cheese']
});

const a = PersonArray.create({
  name: 'Stefan Penner',
  addItem() {
    this.get('shoppingList').pushObject('bacon');
  }
});

const b = PersonArray.create({
  name: 'Robert Jackson',
  addItem() {
    this.get('shoppingList').pushObject('sausage');
  }
});

console.log(1,a.get('shoppingList'),b.get('shoppingList'));
a.addItem();
console.log(2,a.get('shoppingList'),b.get('shoppingList'));
b.addItem();
console.log(3,a.get('shoppingList'),b.get('shoppingList'));

const PersonFunc = Ember.Object.extend({
  shoppingList: Ember.computed('name',function() {
    return [this.get('name'), 'egg'];
  })
});

const c = PersonFunc.create({
  name: 'Stefan Penner',
  addItem() {
    this.get('shoppingList').pushObject('bacon');
  }
});

const d = PersonFunc.create({
  name: 'Robert Jackson',
  addItem() {
    this.get('shoppingList').pushObject('sausage');
  }
});

console.log(4,c.get('shoppingList'),d.get('shoppingList'));
c.addItem();
console.log(5,c.get('shoppingList'),d.get('shoppingList'));
d.addItem();
console.log(6,c.get('shoppingList'),d.get('shoppingList'));

const PersonFuncInit = Ember.Object.extend({
  init() {
    this.set('shoppingList', Ember.computed('name',function() {
    return [this.get('name'), 'egg'];
  }));
  }
});

const e = PersonFuncInit.create({
  name: 'Stefan Penner',
  addItem() {
    this.get('shoppingList').pushObject('bacon');
  }
});

const f = PersonFuncInit.create({
  name: 'Robert Jackson',
  addItem() {
    this.get('shoppingList').pushObject('sausage');
  }
});

console.log(7,e.get('shoppingList'),f.get('shoppingList'));
e.addItem();
console.log(8,e.get('shoppingList'),f.get('shoppingList'));
f.addItem();
console.log(9,e.get('shoppingList'),f.get('shoppingList'));

export default Ember.Controller.extend({});

templates.application.hbs

Look at Console

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": true,
    "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"
  }
}