2nd arg of document.createElement should be an object

third_party/WebKit/Source/core/dom/Document.idl

 /*
  * Copyright (C) 2006, 2007, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006, 2007 Samuel Weinig <sam@webkit.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 157 matching lines @@
                                                                                    [Default=Undefined] optional unrestricted float rotationAngle,
                                                                                    [Default=Undefined] optional unrestricted float force);
     [RuntimeEnabled=Touch] TouchList createTouchList(Touch... touches);
 
     // Custom Elements
     // http://w3c.github.io/webcomponents/spec/custom/#extensions-to-document-interface-to-register
     // FIXME: The registerElement return type should be Function.
     [CallWith=ScriptState, CustomElementCallbacks, RaisesException, MeasureAs=DocumentRegisterElement] CustomElementConstructor registerElement(DOMString type, optional ElementRegistrationOptions options);
     // http://w3c.github.io/webcomponents/spec/custom/#extensions-to-document-interface-to-instantiate
     // FIXME: The typeExtension arguments should not be nullable.
-    [CustomElementCallbacks, PerWorldBindings, RaisesException] Element createElement(DOMString localName, DOMString? typeExtension);
-    [CustomElementCallbacks, RaisesException] Element createElementNS(DOMString? namespaceURI, DOMString qualifiedName, DOMString? typeExtension);
+    [CustomElementCallbacks, PerWorldBindings, RaisesException] Element createElement(DOMString localName, (ElementCreationOptions or DOMString) options);

[Yuki, 2016/09/15 08:01:39]

Just drop-by: The spec is saying |optional ElementCreationOptions| and the old
implementaion was |DOMString?|, so should we keep supporting undefined, too?

Should be (ElementCreationOptions? or DOMString), or something like that?

[Anton Obzhirov, 2016/09/21 15:05:12]

Sorry for late reply. As for DOMString? there is a todo somewhere to make second
string argument not nullable. in Firefox it is not.
As for the optional part there is Element createElement(DOMString localName)
declaration which will be called in the case of one argument. Probably
the two createElement declarations can be merged with making the second argument
optional.

+    [CustomElementCallbacks, RaisesException] Element createElementNS(DOMString? namespaceURI, DOMString qualifiedName, (ElementCreationOptions or DOMString) options);
 
     // Page Visibility
     // http://www.w3.org/TR/page-visibility/#sec-document-interface
     readonly attribute boolean hidden;
     readonly attribute VisibilityState visibilityState;
 
     // CORS and RFC1918
     // https://mikewest.github.io/cors-rfc1918/#feature-detect
     [RuntimeEnabled=CorsRFC1918, ImplementedAs=addressSpaceForBindings] readonly attribute AddressSpace addressSpace;
 
@@ skipping 17 matching lines @@
     [RuntimeEnabled=ExperimentalContentSecurityPolicyFeatures] attribute EventHandler onsecuritypolicyviolation;
     attribute EventHandler onselectionchange;
     attribute EventHandler onselectstart;
     attribute EventHandler onwheel;
 };
 
 Document implements GlobalEventHandlers;
 Document implements ParentNode;
 Document implements NonElementParentNode;
 Document implements DocumentOrShadowRoot;