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- This WPT test may be referenced by the following Test IDs:
- /html/syntax/parsing/custom-element-reparenting-shadow-cycle.html - WPT Dashboard Interop Dashboard
<!DOCTYPE html>
<meta charset="utf-8">
<title>Parser element insertion: a custom element constructor creates a cycle through its own shadow root</title>
<link rel="help" href="https://html.spec.whatwg.org/multipage/parsing.html#insert-an-element-at-the-adjusted-insertion-location">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/adoption-agency-reparenting.js"></script>
<body>
<script>
// The constructor runs before the element is inserted. It cannot append the
// intended parent to itself -- "create an element" rejects a constructed
// element with children -- but it can move it into a shadow root, which makes
// the element a host-including inclusive ancestor of the adjusted insertion
// location. The element is dropped, but stays on the stack of open elements.
promise_test(async t => {
const iframe = await parseInIframe(t, `<script>customElements.define('x-a', class extends HTMLElement { constructor() { super(); if (window.el) return; window.el = this; window.b = document.body; window.root = this.attachShadow({mode: 'open'}); window.root.appendChild(window.b) } })<\/script><body><x-a><p>x</p></x-a>`);
const w = iframe.contentWindow, d = iframe.contentDocument;
assert_equals(d.body, null, "the html element no longer has a body child");
assert_array_equals([...d.documentElement.children].map(e => e.localName), ["head"],
"the document element is left with only its head child");
assert_equals(w.el.parentNode, null, "the custom element was dropped on the floor");
assert_equals(w.root.firstChild, w.b, "body stayed in the custom element's shadow root");
assert_equals(tree(w.b), ``, "the custom element was not inserted into body");
assert_equals(tree(w.el), `<p>["x"]`, "following content went into the dropped element");
}, "Custom element constructor moves the intended parent into its own shadow root");
</script>