New Twiddle

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  index: Ember.inject.controller('index'),
  indexIsClicked: Ember.computed.alias("index.isClicked"),
    
  isIndexClicked: Ember.observer('index.isClicked', function() {
    alert("its changed to " + this.get("indexIsClicked"));
  })
});

application.template.hbs

{{outlet}}
<br>
Is index clicked: <b>{{indexIsClicked}}</b>
<br>

index.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  isClicked: false,
  actions: {
    clicked() {
      console.log("change the isClicked value") ;
      this.toggleProperty('isClicked');
    }
  }
});

index.route.js

import Ember from 'ember';

export default Ember.Route.extend({
});

index.template.hbs

<div {{action "clicked"}}>Click me</div>

twiddle.json

{
  "version": "0.4.16",
  "EmberENV": {
    "FEATURES": {}
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.1.0/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.1.0/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.1.0/ember-template-compiler.js"
  }
}