);
  assert_equals(target.children.length, 1);
}, 'Throwing exception in customized built-in constructor should not crash and should return correct element type (video)');
</script>


<script>
class MyCustomForm extends HTMLFormElement {
  constructor() {
  super();
  throw new Error();
  }
}
customElements.define('custom-form', MyCustomForm, { extends: 'form' });
</script>
<form id=targetform is='custom-form'> <label></label><input> </form>
<script>
test(t => {
  let target = document.getElementById('targe