css/cssom/cssstyledeclaration-properties.html

<!doctype html>
<title>CSS Test: CSSStyleDeclaration properties are defined as WebIDL attributes, not using getOwnPropertyNames()</title>
<link rel="author" href="mailto:emilio@crisal.io" title="Emilio Cobos Álvarez">
<link rel="author" href="https://mozilla.org" title="Mozilla">
<link rel="help" href="https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-_camel_cased_attribute">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
  test(function() {
    let declaration = document.documentElement.style;
    assert_true(declaration instanceof CSSStyleDeclaration, "Should be a CSStyleDeclaration");
    assert_true("color" in declaration, "Should support the color property");
    assert_false(declaration.hasOwnProperty("color"), "shouldn't have an own property for WebIDL attributes");
  });
</script>