problem with html-file in addon

Flow
1

I’m trying to create an addon, this is the html-file for it [signin.html]
(https://github.com/berndhopp/joscha/blob/master/src/main/resources/META-INF/resources/frontend/addon/joscha/signin.html)

problem is, when I run it I get a “(NotSupportedError) : Failed to execute ‘attachShadow’ on ‘Element’: This element does not support attachShadow”. The client-side code is virtually undebuggable (gwt js), but something obviously is wrong with the html file, I just have no clue what it is.

2

I also have a demo-project for it, but you need to install joscha to your lokal maven repo in order to run it

https://github.com/berndhopp/joscha-demo

3

I removed everything that is not necessary in the html, but I still get the same error:


<link rel="import" href="../../bower_components/polymer/polymer.html">
<link rel="import" href="../../bower_components/vaadin-button/vaadin-button.html">

<dom-module id="signin">
    <template>
        <vaadin-button id="button">
        </vaadin-button>
    </template>
    <script>
        class Signin extends Polymer.Element{
            static get is(){
                return 'signin-element';
            }
        }
        customElements.define(Signin.is, Signin);
    </script>
</dom-module>
4

I tried replacing the vaadin-button with just the text ‘hello world’ to see if the vaadin-button is the problem. now I dont get any errors, but the shadow-dom is not attached to the element either. In the browser, I just get

<signin provider="google" app-public-key="appID goes here" style="width: calc(99.9% - 0rem); margin-left: 0px; margin-right: 0px;"></signin>

with no shadow-dom.