Computed + Runloop

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',  
  a: Ember.computed('b', 'c', {
    get() {
      if (this.get('amountOfCalcs') === undefined) {
        this.set('amountOfCalcs', 0);
      }
      else {
        this.set('amountOfCalcs', this.get('amountOfCalcs') + 1)
      }      
      return this.get('b') + this.get('c');
    }
  }),
  b: "This is B!",
  c: "This is C!",
  amountOfCalcs: undefined,
  actions: {
    startRun(){      
      Ember.run(() => {
        this.set('b', "B is changed!");
        this.set('c', "C is changed!");
      })
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<button {{action "startRun"}}>Start run loop!</button>
<br>
{{a}}
<br>
{{amountOfCalcs}}
<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.8.0",
    "ember-data": "2.8.0",
    "ember-template-compiler": "2.8.0",
    "ember-testing": "2.8.0"
  },
  "addons": {}
}