New Twiddle

components.my-component.js

import Ember from 'ember';

const {
  observer
} = Ember;

export default Ember.Component.extend({
  thing: null,
  
  optionsObserver: observer('thing.{prop3}', function () {
    console.log('observer fired')
  }),
  
  didUpdateAttrs() {
    this._super(...arguments);
    
  	console.log('didUpdateAttrs');
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  init() {
    this._super(...arguments); 
    
    this.set('myThing', Ember.Object.create({
      prop1: 'a',
      prop2: 'b'
    }));
  },
  
  actions: {
    changeProp() {
      console.log('changeProp');
      this.get('myThing').set('prop3', Math.floor(Math.random()*10)); 
    }
  }
  
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
<h3>My-component</h3>
{{my-component thing=myThing}}

<hr />
<button type="button" {{action 'changeProp' }}>Change prop</button>
<br>
<br>

templates.components.my-component.hbs

<div>
 Prop1: {{thing.prop1}} <br />
 Prop2: {{thing.prop2}} <br />
 Prop3: {{thing.prop3}}
</div>

twiddle.json

{
  "version": "0.7.2",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "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/2.4.4/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.4.3/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.4/ember-template-compiler.js"
  }
}