New Twiddle

application.controller.js

import Ember from 'ember';

function trackPropertyChanges(defaultValue) {
  var value = defaultValue;
  
  function updateChangedProperty(model, name, property, value) {
      var changedProperties = model.get('changedProperties');
      if (!changedProperties) {
        changedProperties = Ember.Object.create();
      	model.set('changedProperties', changedProperties);  
      }
    
    	var propertyObject = changedProperties.get(property);
    	if (!propertyObject) {
        propertyObject = Ember.Object.create();
        changedProperties.set(property, propertyObject);
      }
    
    	propertyObject.set(name, value);
  }
  
  return Ember.computed({
  	get: function() {
      return value;
    },
    
    set: function(propertyName, propertyValue, oldProperyValue) {
			updateChangedProperty(this, 'old', propertyName, oldProperyValue);
      updateChangedProperty(this, 'new', propertyName, propertyValue);

      value = propertyValue;
      return propertyValue;
    }
  });
}

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  
  test: trackPropertyChanges('TEST'),
  test1: trackPropertyChanges(),
  
  obs: Ember.observer('test', 'test1', function(model, propertyName) {
    var oldValue = this.get('changedProperties.' + propertyName + '.old');
  	var newValue = this.get('changedProperties.' + propertyName + '.new');
    console.log(propertyName, ':', oldValue, ' -> ', newValue);
  })
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>
{{input value=test}}

{{input value=test1}}

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"
  }
}