Failed to construct 'CustomElement': The result must not have attributes

[yshirsath]

Router.js#247 throws this error when run from Cypress integration tests in our GitHub runner.

Versions:

• "lit-element": "^2.3.1"
• "@vaadin/router": "^1.7.2",
• Github runner: ubuntu-latest

Known Facts:

• This issue began occurring around 3/5/24. Previously passing tests now fail with this issue when rerun.
• This issue does not happen when run locally
• This issue is browser agnostic.
• Issue does not occur if we remove vaadin router completely from our source
• Issue does occur with the simplest possible router implementation:

index.ts

const router = new Router(document.querySelector('body'));
router.setRoutes([{path: '/test', component: 'root-view'}], true);

root-view.ts

import { LitElement, html } from "lit-element";

export class RootView extends LitElement {
  render() {
    return html`Hi`;
  }
}

customElements.define("root-view", RootView);

[Artur-]

Sounds like you have a custom element with a constructor that sets attributes

[yshirsath]

Hey @Artur- , thanks for the reply. As you can see there is only one element in our project and it does not in fact have a constructor.