How to create new instance of an extended class of custom elements

Question

I\'m trying the example from google developer site and I\'m getting Error: \"TypeError: Illegal constructor. What\'s wrong and How to fix it?

class FancyButt         


        

Answer 1

Blink, the web engine that currently implements Custom Element v1 (in Chrome v53+ for example) only supports autonomous custom elements: see open Blink bug.

If you want to define customized built-in elements (i.e. extension), you'll need to use a polyfill like the one from Web Reflection.

Alternatly, you can still use the Custom Element v0 syntax (document.registerElement).

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Update #3

Since october 2018, they work natively with Chrome 67+ and Firefox 63+ :-)