New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  actions: {
    toggleShouldDisable(){this.set('shouldDisable', ! this.get('shouldDisable'));},
  },
});

styles.app.css

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

:disabled {
 border: thin solid red;
}

templates.application.hbs

<button {{action 'toggleShouldDisable'}}> toggle</button>
<button
  disabled={{if shouldDisable 'disabled' ''}}>am i disabled?</button>
<br>
<br>

twiddle.json

{
  "version": "0.10.6",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.9.0",
    "ember-data": "2.9.0",
    "ember-template-compiler": "2.9.0",
    "ember-testing": "2.9.0"
  },
  "addons": {}
}