New Twiddle

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  foo: 'value of foo'
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{beautify foo}}
<br>
<br>

helpers.beautify.js

import Ember from 'ember';

export function beautify(params/*, hash*/) {
  var str= new Ember.Handlebars.SafeString(params[0].replace(/_/g, ' '));
    return str;
}

export default Ember.Helper.helper(beautify);

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"
  }
}