New Twiddle

application.controller.js

import Ember from 'ember';

var FilePath = Em.Object.extend({
   default: null,
   fileName: Em.computed.oneWay('default'),
   path: Em.computed('fileName', function() {
     return '/path/' + this.get('fileName');
   })
 });

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  
  filePath: Ember.computed(function(){
    return FilePath.create();
  }),
  
  actions: {
    setFilePath() {
      let filePath = this.get('filePath');
      filePath.set('default', 'untitled.txt');
      filePath.set('fileName', 'image.jpeg');
    }
    
  }
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
{{filePath.path}}
<br>
{{outlet}}
<br>
<br>

<button {{action 'setFilePath'}}>updatePath</button>

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": "release",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.2.0/ember-data.js",
    "ember-template-compiler": "release"
  }
}