JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a">start</div>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script src="http://builds.handlebarsjs.com.s3.amazonaws.com/handlebars-v1.1.2.js"></script>
<script src="http://builds.emberjs.com/tags/v1.2.0/ember.min.js"></script>

JavaScript

var emptyEmberObjectClass = Ember.Object.extend({});
var container = Ember.Object.extend({
  data: Ember.A([
    emptyEmberObjectClass.create({yo:1}),
    emptyEmberObjectClass.create({yo:2}),
    emptyEmberObjectClass.create({yo:3})
  ]),
  computedData: Ember.computed('[email protected]', function(){
    var sum = 0;
    this.get('data').forEach(function(data){
      sum = sum + data.yo;
    });
    return sum;
  }),
  test: Ember.observer('computedData', function(){
    Ember.$('#a').html('woohoO!');
  })
}).create();
var existingItem = container.get('data');
existingItem.objectAt(0).set('yo', 50);