chromium/third_party/blink/web_tests/custom-elements/spec/insert-a-node-try-to-upgrade.html

<!DOCTYPE html>
<title>Custom Elements: Insert a node should try to upgrade</title>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="resources/custom-elements-helpers.js"></script>
<body>
<script>
'use strict';

function assert_invocations(invocations, element, length, i) {
  assert_equals(invocations.length, length, length == 2 ? 'inserting into different node should enqueue connectedCallback again' : 'inserting an element should enqueue connectedCallback reaction');
  assert_array_equals(invocations[i].slice(0, 2), ['connected', element], 'inserting "custom" element should enqueue a connectedCallback reaction');
  assert_array_equals(invocations[i][2], [], 'connectedCallback should be invoked with empty argument list');
}

// Insert a node
// https://dom.spec.whatwg.org/#concept-node-insert
// 6.5.2.1 If inclusiveDescendant is custom, then enqueue a custom element callback reaction 
// with inclusiveDescendant, callback name "connectedCallback", and an empty argument list.
test_with_window(w => {
  let element = w.document.createElement('a-a');
  let invocations = [];
  w.customElements.define('a-a', class extends w.HTMLElement {
    connectedCallback() { invocations.push(['connected', this, arguments]); }
  });
  w.document.body.appendChild(element);
  assert_invocations(invocations, element, 1, 0);
  w.document.head.appendChild(element);
  assert_invocations(invocations, element, 2, 1);
}, 'Insert a node that is "custom" should enqueue connectedCallback');

// 6.5.2.2. try to upgrade inclusiveDescendant.
// Try to upgrade an element
// https://html.spec.whatwg.org/multipage/scripting.html#concept-try-upgrade
test_with_window(w => {
  let element = w.document.createElement('a-a');

  w.customElements.define('a-a', class extends w.HTMLElement {
    constructor() {
      super();
      this.is_upgraded = true;
    }
  });
  assert_false('is_upgraded' in element);
  assert_false(element.matches(':defined'));

  w.document.body.appendChild(element);
  assert_true(element.is_upgraded);
  assert_true(element.matches(':defined'));
}, 'Insert a node should try to upgrade');
</script>
</body>