custom-elements/form-associated/focusability.html

<!DOCTYPE html>
<title>Focusability of form-associated custom elements</title>
<link rel="author" title="Michael[tm] Smith" href="mailto:mike@w3.org">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<x-foo></x-foo>
<x-bar tabindex=0></x-bar>
<x-baz tabindex=0 disabled></x-baz>
<script>
  test(() => {
    customElements.define(
        'x-foo',
        class Foo extends HTMLElement {
            static formAssociated = true;
        }
    );
    const foo = document.querySelector('x-foo');
    foo.focus();
    assert_false(document.activeElement === foo,
      "FACE without tabindex is not focusable.");
    customElements.define(
        'x-bar',
        class bar extends HTMLElement {
            static formAssociated = true;
        }
    );
    const bar = document.querySelector('x-bar');
    bar.focus();
    assert_true(document.activeElement === bar,
      "FACE with tabindex is focusable.");
    customElements.define(
        'x-baz',
        class baz extends HTMLElement {
            static formAssociated = true;
        }
    );
    const baz = document.querySelector('x-baz');
    baz.focus();
    assert_false(document.activeElement === baz,
      "Disabled FACE with tabindex is not focusable.");
  });
</script>
</html>