Multiple properties of an object in a single observer

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  buttonvalues : function(){
    	return {button1:"",button2:"",button3:""};
  }.property(),
  handleChange : Ember.observer("buttonvalues.{button1,button2,button3}",function(){
    		this.set("changedvalue",arguments[1]);
  }),
  actions:{
    updateValue :function(buttonno)
    {
    		this.set("buttonvalues.button"+buttonno,Math.floor(Math.random()*10));
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
<button {{action "updateValue" 1}}>Update button 1</button>
<button {{action "updateValue" 2}}>Update button 2</button>
<button {{action "updateValue" 3}}>Update button 3</button><br><br>
Button 1 : {{buttonvalues.button1}}<br><br>
Button 2 : {{buttonvalues.button2}}<br><br>
Button 3 : {{buttonvalues.button3}}<br><br>
Changed value : {{changedvalue}}
<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"
  }
}