New Twiddle

components.x-list.js

import Ember from 'ember';

export default Ember.Component.extend({
  items: [],
  itemsCount: 0,
  inputText: null,
  
  onItemsChange: Ember.observer('items.[]', function() {
    this.set('itemsCount', this.get('items.length'));
  }),
  
  actions: {
    addItem() {
    	this.get('items').pushObject(this.get('inputText'));
      this.set('inputText', null);
    }
  }
});

controllers.index.js

import Ember from 'ember';

export default Ember.Controller.extend({
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.is-empty h2 {
  color: red;
}

templates.application.hbs

{{outlet}}

templates.components.x-list.hbs

<h2>{{yield}}</h2>

<ul>
	{{#each items as |item|}}
  	<li>
    	{{item}}
    </li>
  {{/each}}
</ul>

<p>
	Count: {{itemsCount}}
</p>

{{input
	type="text"
  value=inputText}}
  
<button
	type="button"
  onclick={{action "addItem"}}>
	Add
</button>

templates.index.hbs

{{#x-list}}
	Favorite Animals
{{/x-list}}

{{#x-list}}
	Favorite Colors
{{/x-list}}

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"
  }
}