Timer

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  delta: 0,
  _interval: null,
  startTime: null,
  timer: Ember.computed('delta', function() {
    const that = this;
    if (this._interval === null) {
  		this.set('startTime', Date.now());
  		this._interval = setInterval(function() {
  			const start = that.get('startTime');
  			that.set('delta', Date.now() - start);
      }, 1000);
		}
                                       
  	return this.get('delta');
  }),
});

application.template.hbs

<h1>Welcome to {{timer}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.5.3",
  "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/2.3.1/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.3.3/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}