custom-elements/historical.html

<!doctype html>
<title>Custom Elements v0 features</title>
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<script>
test(() => {
  assert_false('registerElement' in document)
}, 'document.registerElement should not exist')

// These tests should pass as long as v0 isn't supported:
// v0: a 2nd string argument for createElement.
// v1: a ElementCreationOptions (dictionary) argument.
test(() => {
  try {
    const element = document.createElement('x', 'string')
    // If neither v0/v1 are supported, then there should be no is attribute.
    assert_false(element.hasAttribute('is'))
  } catch (e) {
    // If v1 is supported, then converting string to dictionary should throw.
    assert_throws(new TypeError, function() { throw e })
  }
}, 'document.createElement(localName, "string") should not work')

// createElementNS is analagous, but for the 3rd argument
test(() => {
  try {
    const element = document.createElementNS(null, 'x', 'string')
    // If neither v0/v1 are supported, then there should be no is attribute.
    assert_false(element.hasAttribute('is'))
  } catch (e) {
    // If v1 is supported, then converting string to dictionary should throw.
    assert_throws(new TypeError, function() { throw e })
  }
}, 'document.createElementNS(namespace, qualifiedName, "string") should not work')
</script>