observe

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  
  aaa: [],
  
  bbb: Ember.computed('aaa.[]', function(){
    return Math.random();
  }),
  
  lala: Ember.observer('bbb', function(){
    //this.get('bbb');
    console.log('here');
  }).on('init'),
  
  move: (function() {
    let _this = this;
    setInterval(function() {
    	_this.get('aaa').pushObject('a');
    }, 1000);
  }).on('init')
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{#each aaa as |a|}}
	{{a}}
{{/each}}
<br>
<br>

twiddle.json

{
  "version": "0.5.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.2.0/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}