New Twiddle

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  actions: {
    hoverIn() {
      this.set('hovering', true); 
      console.log('hoverIn');
    },
    hoverOut() {
      this.set('hovering', false);
      console.log('hoverOut');
    }
  }
});

controllers.application.js

import Ember from 'ember';

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>
{{my-component}}

templates.components.my-component.hbs

<h1 class={{if hovering 'cool' 'not-cool'}} onMouseEnter={{action 'hoverIn'}} onMouseLeave={{action 'hoverOut'}}>I am {{hovering}}</h1>

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": {}
}