WebIDL/ecmascript-binding/has-instance.html

<!doctype html>
<meta charset="utf-8">
<title>instanceof behavior</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<iframe></iframe>

<script>
test(function() {
  var obj = Object.create(Element.prototype);
  assert_true(obj instanceof Element);
  assert_true(obj instanceof Node);
  assert_false(obj instanceof Attr);
}, "Manually-constructed prototype chains are correctly handled by instanceof");

test(() => {
  // This tests that the historical override of [[HasInstance]] was removed:
  // https://github.com/heycam/webidl/pull/356
  assert_false(document.body instanceof frames[0].Element);
}, "instanceof must return false across different globals, for platform objects");

test(() => {
  assert_false(EventTarget.hasOwnProperty(Symbol.hasInstance));
}, "platform objects do not have Symbol.hasInstance installed");
</script>