New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  names: ['dani'],
  
  init() {
    this._super(...arguments);
		let length = this.get('names.length');
    alert(`Length before mutate: ${length}`);
  },
  
  actions: {
    show() {
  		let length = this.get('names.length');
      alert(`Length: ${length}`);
    }
  }
});

helpers.my-helper.js

import Ember from 'ember';

export function myHelper([arr]/*, hash*/) {
  arr.pushObject('frank');
  return arr;
}

export default Ember.Helper.helper(myHelper);

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>
From helper: {{my-helper names}}
<br><br><br>
<button {{action 'show'}}>show me the length!</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"
  }
}