New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  arr: Ember.A([]),
  
  theLength: Ember.computed('arr[]', function() {
    return this.get('arr').length;
  }),
  
  actions: {
    push(arr, obj) {
      arr.pushObject(obj);
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
<button {{action "push" arr 5}}>
  Push another element (currently {{theLength}})
</button>
<ul>
{{#each arr as |l|}}
  <li>{{l}}</li>
{{/each}}
</ul>
<br>
<br>

twiddle.json

{
  "version": "0.13.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-template-compiler": "2.16.2",
    "ember-testing": "2.16.2"
  },
  "addons": {
    "ember-data": "2.16.3"
  }
}