Observing an array

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  init() {
    this._super(...arguments);
    this.set('myArray', []);
    this.set('x', 3);
    this.set('arraySum1InvocationCount', 0);
    this.set('arraySum2InvocationCount', 0);
  },
  
  arraySum1: Ember.computed('myArray', function() {
    this.incrementProperty('arraySum1InvocationCount');
  	return this.get('myArray').reduce((item, acc) => acc + item, 0);
  }),
  
  arraySum2: Ember.computed('myArray.[]', function() {
    this.incrementProperty('arraySum2InvocationCount');
  	return this.get('myArray').reduce((item, acc) => acc + item, 0);
  }),
  
  actions: {
    replaceArray() {
      this.set('myArray', []);
    },
    addToArray(item) {
      this.get('myArray').pushObject(item);
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}

<p><code>arraySum1</code> {{arraySum1}}</p>
<p><code>arraySum2</code> {{arraySum2}}</p>

<p>
	<code>arraySum1</code> computed property has been re-calculated {{arraySum1InvocationCount}} time(s)
</p>

<p>
	<code>arraySum2</code> computed property has been re-calculated {{arraySum2InvocationCount}} time(s)
</p>


<p>
<button onClick={{action "replaceArray"}}>Click to set myArray to a new array</button>
</p>
<p>
	<button onClick={{action "addToArray" x}}>Click to add an item to myArray without replacing it</button>
	{{input value=x}}
</p>
<br>
<br>

twiddle.json

{
  "version": "0.13.0",
  "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"
  }
}