shared-component-state

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle'
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>

{{t-shirt title="Will" sizes="md lg"}}
{{t-shirt title="Tom" sizes="md lg"}}

<br>
<br>

t-shirt.component.js

import Ember from 'ember';

const { String: { w } } = Ember;

export default Ember.Component.extend({
  sizes: [],
  
  setSizes: Ember.on('init', function() {
    let { sizes } = this.attrs;
    this.sizes = w(sizes);
  }),
  
  actions: {
    addSize(event) {
      this.get('sizes').pushObject(event.target.value);
    }
  }
});

t-shirt.template.hbs

<h1>{{title}}</h1>

<ul>
{{#each sizes as |size|}}
  <li>{{size}}</li>
{{/each}}
</ul>

<input onchange={{action "addSize"}}>

twiddle.json

{
  "version": "0.4.17",
  "EmberENV": {
    "FEATURES": {}
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.2.0/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}