What's this?

[chisholmd]

Failed to load module script: The server responded with a non-JavaScript MIME type of "text/html". Strict MIME type checking is enforced for module scripts per HTML spec.

[andreasbm]

Thanks for opening this issue! It would be of great help if you are able to provide some code or details on how to reproduce the problem you are describing.

The error occurs when trying to import a html file as a module file. The following code reproduces it.

const routerSlot = document.querySelector("router-slot");
routerSlot.add([
  {
    path: "wrong-import",
    component: () => import("/path/to/file.html")
  },
  {
    path: "**",
    redirectTo: "wrong-import"
  }
]);

Try to change the file you are importing to a module that exports a custom element as default instead. It could look something like this:

// path/to/file.js
import { LitElement, html } from "https://unpkg.com/lit-element?module";

export default class MyPage extends LitElement {
  render () {
    return html`
      <p>Hello World</p>
    `;
  }
}

customElements.define("my-page", MyPage);