New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  anArray: Ember.A([]),
  actions: {
    update(){
      this.get('anArray').pushObject('hello hello'); 
    }
  }
});

helpers.my-helper.js

import Ember from 'ember';
let timesCalled = 1;
export function myHelper(params/*, hash*/) {
  console.log(timesCalled);
  return timesCalled++;
}

export default Ember.Helper.helper(myHelper);

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
`anArray.length`: {{anArray.length}}
<br>
Number of times `my-helper` is called: {{my-helper anArray}}
<br>
<button {{action 'update'}}>Trigger Update</button>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}