New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  init() {
  	this._super(...arguments);
    this.set('ads', [
      Ember.Object.create({ rotationWeight: 3 }),
      Ember.Object.create({ rotationWeight: 5 }),
      Ember.Object.create({ rotationWeight: 2 }),
      Ember.Object.create({ rotationWeight: 1 })
    ]);
    
    Ember.run.later(() => {
    	this.get('ads.firstObject').set('rotationWeight', 100);
    }, 1000);
  },
  groupTotal: Ember.computed('[email protected]', function() {
    return this.get('ads').reduce((sum, ad) => {
      return sum + ad.get('rotationWeight')
    }, 0);
  })
});

templates.application.hbs

Group Total: {{groupTotal}}

twiddle.json

{
  "version": "0.13.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}