New Twiddle

components.bar-baz.js

import Ember from 'ember';
import DummyMixin from '../mixins/dummy-mixin'

const BarBaz = Ember.Component.extend({
  handleClick() {
    console.log('bar-baz --- reopenClass');
		// This will throw error
		this.popup();
    
    // But this will work
    this.constructor.popup();
  }  
});

BarBaz.reopenClass(DummyMixin)

export default BarBaz;

components.foo-bar.js

import Ember from 'ember';
import DummyMixin from '../mixins/dummy-mixin'

export default Ember.Component.extend(DummyMixin, {
  handleClick() {
    console.log('foo-bar --- Mixined');
		this.popup();
  }
});

controllers.application.js

import Ember from 'ember';

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

mixins.dummy-mixin.js

import Ember from 'ember';

export default Ember.Mixin.create({
  testProp: 'TEST_PROP',
  popup() {
    console.log(`From inside popup --- ${this}`);
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{foo-bar}}
{{bar-baz}}
<br>
<br>

templates.components.bar-baz.hbs

{{testProp}}
<button onclick={{action handleClick}}>Bar Baz</button>

templates.components.foo-bar.hbs

{{testProp}}

<button onclick={{action handleClick}}>Click Foo Bar</button>

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"
  }
}