title: HTML5 ES6 Custom-Elements extending HTMLTextAreaElement crashes illegal constructor
body: <p>i need to extend a custom element from HTMLTextAreaElement for using in a form and fetch value directly. but i allways get Illegal Constructor Message</p>
  
  <p>HTML:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
    &lt;head&gt;
    &lt;/head&gt;
    &lt;body&gt;
      &lt;div&gt;
        &lt;working-element&gt;&lt;/working-element&gt;
      &lt;/div&gt;
      &lt;div&gt;
        &lt;crashing-element&gt;&lt;/crashing-element&gt;
      &lt;/div&gt;
    &lt;/body&gt;
    &lt;script src="myScript.js"&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>Typescript (compiled as ES6 to myScript.js):</p>
  
  <pre><code>// all works fine
  class newElementWorks extends HTMLElement {
    constructor(){
      super();
      console.log('newElementWorks');
    }
  }
  customElements.define('working-element', newElementWorks);
  
  // this one crashes on super() call
  class newElementCrash extends HTMLTextAreaElement {
    constructor(){
      super();
      console.log('newElementCrash');
    }
  }
  customElements.define('crashing-element', newElementCrash);
  </code></pre>
  
  <p>the script is executed on Chrome Version 63.0.3239.132 that supports ES6 and Custom-Element</p>
  
  <p>i allready tried to include <a href="https://github.com/webcomponents/custom-elements" rel="nofollow noreferrer">webcomponents/custom-elements</a> polyfill</p>
  
  <p>do you have any idea why extending from other than HTMLElement crashes?</p>