Thanks for filing this! Tentatively me. String to dictionary is an (ancient) spec change we never implemented.

Our implementation separates v0 and v1 custom elements pretty explicitly. We will not support a string argument for v1 elements. We don't support v1 customized built-in elements yet.

We'll deprecate the string version for v0 elements along with the rest of v0.

Hi Dominic,

I could help with this one. Are you guys already implementing v1 customized built-in elements? May be I could jump in.
 

Sure, please go ahead.

I want very specific way of handling this parameter when customized built-in elements are implemented (soon.)

For now, just handling the dictionary, but also accepting a string (maybe using toString?) but with a deprecation warning for the string, would be good.

Thanks, will do.

Hi, I made a draft patch.
https://codereview.chromium.org/2334223005

Plz check if I am going in the right direction.

Hi Anton, what's happening with this? The blink-dev thread got enough LGTMs to ship the new option, but not add the deprecation message to the string, string version yet--just the use counter.

It would be good to get this in the tree soon. yurak is implementing customized built-in elements which needs this parameter.

Hi, sorry for delay - was on holiday last week and was actually waiting for your reply on one of my emails. Will update the patch and try to merge it today.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fc17d505758c284f99624ac69b6e2fb72ea7b623

commit fc17d505758c284f99624ac69b6e2fb72ea7b623
Author: a.obzhirov <a.obzhirov@samsung.com>
Date: Thu Oct 27 19:33:32 2016

2nd arg of document.createElement should be an object

This patch adds a dictionary as a second argument for document.createElement.
See https://dom.spec.whatwg.org/#dom-document-createelement.

BUG= 637353 

Review-Url: https://codereview.chromium.org/2334223005
Cr-Commit-Position: refs/heads/master@{#428111}

[add] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/LayoutTests/fast/dom/custom/create-element-second-arg.html
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/bindings/core/v8/BUILD.gn
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/bindings/core/v8/V0CustomElementConstructorBuilder.cpp
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/core/core_idl_files.gni
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/core/dom/Document.cpp
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/core/dom/Document.h
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/core/dom/Document.idl
[add] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/core/dom/ElementCreationOptions.idl
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/core/dom/TreeScopeTest.cpp
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/core/dom/custom/CustomElementUpgradeSorterTest.cpp
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/third_party/WebKit/Source/core/frame/UseCounter.h
[modify] https://crrev.com/fc17d505758c284f99624ac69b6e2fb72ea7b623/tools/metrics/histograms/histograms.xml

Hi Dominic,

The patch is merged without the deprecation message. I guess now we would need to wait some time to get use count for string argument. Do we keep this bug open for now?

Awesome, thank you so much. I've filed Issue 660758 to track the deprecation since it will take ages for the use counter data to come in.