Extend DOM elements ES6

es6-dom-extend.js

class SmartButton extends HTMLButtonElement {
  constructor() {}
}
let sb = new SmartButton();
document.body.appendChild(sb);

/*
I get the below error:

TypeError: Failed to execute 'appendChild' 
on 'Node': parameter 1 is not of type 'Node'.

It needs a document.registerElement as well? :/

But then what's the whole point of extending, it can just do a Object.create()
*/

class CustomElement extends HTMLElement {
    // Fires when an instance of the element is created.
    createdCallback() {

    };
    // Fires when an instance was inserted into the document.
    attachedCallback() {

    };
    // Fires when an instance was removed from the document.
    detachedCallback() {

    };
    // Fires when an attribute was added, removed, or updated.
    attributeChangedCallback(attr, oldVal, newVal) {

    };
}

document.registerElement('custom', CustomElement);

let element = document.createElement('custom');

document.body.appendChild(element);