New Twiddle

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  actions: {
    add() {
      this.get('foo').pushObject(5);
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  ctrlFoo: [1,2,3]
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{#each ctrlFoo as |i|}}{{i}},{{/each}}
<hr>
{{my-component foo=(readonly ctrlFoo)}}
<br>
<br>

templates.components.my-component.hbs

{{foo.length}}
<button {{action 'add'}}>add</button>

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": {}
}