custom-elements/overwritten-customElements-global.html

<!DOCTYPE html>
<meta charset="utf-8">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<body>
<script>
"use strict";

test(() => {
  class SomeElement1 extends HTMLElement {}
  customElements.define("some-element-1", SomeElement1);

  const savedCustomElements = Object.getOwnPropertyDescriptor(window, "customElements");
  Object.defineProperty(window, "customElements", { value: {}, configurable: true });

  const element = document.createElement("some-element-1");
  assert_true(element instanceof SomeElement1);

  Object.defineProperty(window, "customElements", savedCustomElements);
}, "Custom elements can still be created after `window.customElements` is overwritten.");

test(() => {
  class SomeElement2 extends HTMLElement {}
  customElements.define("some-element-2", SomeElement2);

  const savedCustomElements = Object.getOwnPropertyDescriptor(window, "customElements");
  Object.defineProperty(window, "customElements", { value: {}, configurable: true });

  const element = new SomeElement2();
  assert_true(element instanceof SomeElement2);

  Object.defineProperty(window, "customElements", savedCustomElements);
}, "Custom elements can still be constructed after `window.customElements` is overwritten.");

test(() => {
  class SomeElement3 extends HTMLElement {}
  customElements.define("some-element-3", SomeElement3);

  const savedCustomElements = Object.getOwnPropertyDescriptor(window, "customElements");
  delete window.customElements;

  const element = document.createElement("some-element-3");
  assert_true(element instanceof SomeElement3);

  Object.defineProperty(window, "customElements", savedCustomElements);
}, "Custom elements can still be created after `window.customElements` is deleted.");

test(() => {
  class SomeElement4 extends HTMLElement {}
  customElements.define("some-element-4", SomeElement4);

  const savedCustomElements = Object.getOwnPropertyDescriptor(window, "customElements");
  delete window.customElements;

  const element = new SomeElement4();
  assert_true(element instanceof SomeElement4);

  Object.defineProperty(window, "customElements", savedCustomElements);
}, "Custom elements can still be constructed after `window.customElements` is deleted.");
</script>