Class on component

components.my-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['foo'],

  didInsertElement() {
		this.set('allOfTheClasses', this.element.classList);
  },
});

controllers.application.js

import Ember from 'ember';

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

templates.application.hbs

{{#my-component class="bar"}}
Boo
{{/my-component}}

templates.components.my-component.hbs

{{yield}}

<p>All of the classes: {{allOfTheClasses}}</p>

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.1.4",
    "ember-template-compiler": "3.1.4",
    "ember-testing": "3.1.4"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}