>This code **will not** work if you transform classes with Babel. See [this issue](https://github.com/w3c/webcomponents/issues/587) for the discussion.
>Include the [custom-elements-es5-adapter](https://github.com/webcomponents/polyfills/tree/main/packages/webcomponentsjs#custom-elements-es5-adapterjs) before you load your web components to fix this issue.
>Include the [custom-elements-es5-adapter](https://github.com/webcomponents/polyfills/tree/master/packages/webcomponentsjs#custom-elements-es5-adapterjs) before you load your web components to fix this issue.