Bug 164114 – DOMStringMap reports properties as non-enumerable

• Component: DOM
• Status: RESOLVED FIXED

[Alexey Shvayka]

Consider the following HTML: `<div id=map data-size=16></div>`.

In Chrome and Firefox, `Object.getOwnPropertyDescriptor(map.dataset, "zoom").enumerable` is `true`.
In Safari it is `false`, but "zoom" gets listed by `Object.keys`.
However, it does not work with `Object.assign` and also reports `false` in `propertyIsEnumerable` check.

From user-land perspective, this disables neat `Object.assign(el1.dataset, el2.dataset)` trick.
For the sake of web compatibility and developer experience, I think Safari should match behavior of other browsers.

[Chris Dumez]

Relevant specs:
- https://heycam.github.io/webidl/#getownproperty-guts (2.7-9)
"""
If O implements an interface with a named property setter, then set desc.[[Writable]] to true, otherwise set it to false.
If O implements an interface with the [LegacyUnenumerableNamedProperties] extended attribute, then set desc.[[Enumerable]] to false, otherwise set it to true.
Set desc.[[Configurable]] to true.
"""

- https://html.spec.whatwg.org/multipage/dom.html#domstringmap
Interface is not marked as [LegacyUnenumerableNamedProperties].

So I believe the DOMStringMap's named properties should be Configurable, Enumerable and Writable (because there is a named setter).

We currently do the complete opposite.

[Chris Dumez]

Created attachment 293237 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 293237 [details]
Patch

Clearing flags on attachment: 293237

Committed r208083: <http://trac.webkit.org/changeset/208083>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.