<!DOCTYPE html>
<html>
<body>
<script type="text/javascript">
class XFoo extends HTMLElement {
  constructor() {
    super();
  }

  static get observedAttributes() {
    return [3.76277868767527e-310, Symbol("Ashitaka"), {}];
  }

  attributeChangedCallback(aName, aOldValue, aNewValue) {
  }
}

customElements.define('x-foo', XFoo);
</script>
</html>
