title: ES6 export extended class and then import it
body: <p>I have a basic class (mobile.js)</p>
  
  <pre><code>class Mobile {
      constructor() {
          ...
      }
      method(msg){
         ...
      }
  }
  module.exports = Mobile;
  </code></pre>
  
  <p>Then I import it to (mobileextended.js);</p>
  
  <pre><code>import Mobile from './mobile';
  
   class MobilePhone extends Mobile {
       method(){
          super.method('hello world!');
       }   
  }
  module.exports = MobilePhone;
  </code></pre>
  
  <p>And in the end I want to import it to mobilephone.js:</p>
  
  <pre><code> import MobilePhone from './mobileextended.js';
  
      MobilePhone.method();
  </code></pre>
  
  <p>How can I make that work in ES6 style? Because now I'm getting Cannot read property 'open' of undefined error.</p>