Selection Add Class

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle',
  selectedItem: null,
  things: [
    { name: 'a' },
    { name: 'b' },
    { name: 'c' }
  ],
  
  actions: {
    selectItem(thing) {
      this.set('selectedItem', thing); 
    }
  }
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<ul>
{{#each things as |thing| }}
  <li><button {{action "selectItem" thing}} type="button">{{thing.name}}</button></li>
{{/each}}
</ul>
<br>
Selected Item: {{selectedItem.name}}
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.4.13",
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.10/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/1.13.13/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/1.13.10/ember-template-compiler.js"
  }
}