New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  init() {
    this._super(...arguments);
    
    this.set('myArray', []);
  },
  
  getNewItem() {
    const items = this.get('items');
    return Math.floor(Math.random() * 100);
  },
  
  myItems1: Ember.computed('myArray', function() {
    return this.get('myArray').join(', ');
  }),
  
  myItems2: Ember.computed('myArray.[]', function() {
    return this.get('myArray').join(', ');
  }),
  
  actions: {
    addItemToArray() {
      this.get('myArray').addObject(this.getNewItem());
    },
    
    addItemAndReplaceArray() {
      const myArray = this.get('myArray');
      const newArray = myArray.concat([this.getNewItem()]);
      
      this.set('myArray', newArray);
    },
  },
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

templates.application.hbs

<h1>computed property lists demo</h1>
<br>
<br>

<p>Try using "Add Item" and "Add and replace" below. Notice that when using "Add Item", only the computed property thas uses `.[]` updates, and when using replace, they both update.</p>

<p>
<button {{action 'addItemToArray'}}>Add Item</button> | <button {{action 'addItemAndReplaceArray'}}>Add and replace</button>
</p>

<p>These are the items: {{myItems1}}</p>
<p>These are the items with .[]: {{myItems2}}</p>


<br>
<br>

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"
  }
}