Weird error message when trying to create webcomponent for Mesop

Here's the error message I keep getting:

It doesn't happen every time though. Occasionally I can get it to show a different error message.

This error message seems to appear when there is an error (but only certain types of errors it seems) in the javascript. This error occurs in dev mode in Mesop (via Pip) and Mesop with Bazel. It does not show up in Prod mode for Mesop via Pip

Example code:

import {
  LitElement,
  html,
} from 'https://cdn.jsdelivr.net/gh/lit/dist@3/core/lit-core.min.js';

import 'https://cdnjs.cloudflare.com/ajax/libs/codemirror/6.65.7/codemirror.js';
import 'https://cdnjs.cloudflare.com/ajax/libs/codemirror/6.65.7/mode/javascript/javascript.js';

class CodeEditorComponent extends LitElement {
  // Comment this properties object out and the code will work
  static properties = {
    code: ({type: String} = 'Hello World!'),
    codeChanged: {type: String},
  };

  constructor() {
    super();
    this.editorView = null;
  }

  createRenderRoot() {
    // Render in light DOM so firebase-ui-auth works.
    return this;
  }

  firstUpdated() {
    this.renderEditor();
  }

  renderEditor() {
    this.editorView = CodeMirror.fromTextArea(this.querySelector('#editor'), {
      mode: 'javascript',
      lineNumbers: true,
      theme: 'default',
      readOnly: false,
    });
  }

  render() {
    return html` <textarea id="editor">
function() { console.log('hello world'); </textarea
    >`;
  }
}

customElements.define('code-editor-component', CodeEditorComponent);

google / mesop

Weird error message when trying to create webcomponent for Mesop #637