test-bindings

components.test-bindings.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['one','two','three'],
  
  extraClasses: function() {
     return ['extra-one', 'extra-two', 'extra-three'].join(' ');
  }.property(),
  
  classNameBindings: ['extraClasses'],
  
  classes: function () {
    return this.get('classNames').join(' ');
  }.property()
});

controllers.application.js

import Ember from 'ember';

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

router.js

import Ember from 'ember';
import config from './config/environment';

const Router = Ember.Router.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('home', { path: '/' });
});

export default Router;

routes.home.js

import Ember from 'ember';

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

templates.application.hbs

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

templates.components.test-bindings.hbs

Component's css classes: {{classes}}

templates.home.hbs

{{test-bindings classNames="a b c"}}

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"
  }
}

View in ember-twiddle.com