Use localName instead of nodeName

[eps1lon]

Due to heave usage of getComputedStyle in jsdom we discovered that Element.prototype.nodeName was a bottleneck. It seems like this isn't the correct property to use for selectors but Element.prototype.localName (which is way cheaper in jsdom).

See:

• CSS type selectors

• CSS qualified names

• feat: Cache Element.prototype.tagName jsdom/jsdom#3008

  -- @domenic feat: Cache Element.prototype.tagName jsdom/jsdom#3008 (comment)

It isn't clear to me how to test these changes extensively. I quickly verified it in ./test/jquery/jquery, ./test/html5/, ./test/slick/Runner/runner (all in Chrome 84) and by using this PR in jsdom's yarn test-wpt. All test suites still pass with these changes.

[dperini]

@eps1lon
I am going to do the full testing and accept this change if it doesn't produce regressions.
Thank you for the suggestion.

[ExE-Boss]

localName reflects the element name without ASCII upper‑casing, so it will be "DiV" and not "DIV".

[dperini]

@ExE-Boss
Thank you for the help following with us.
In both Firefox and Chrome (latest versions):
document.createElement('DiV').localName == 'div'
instead of 'DiV'. Any thought ?

If this is true then `localName' is the lower-casing version of the tag name.

Recall that this differentiation was introduced to support mixed namespaces in the same document (SGV mostly).
Do you believe we are at risk of introducing regressions related to that multi-namespaces support with these changes ?

[eps1lon]

Seems like we could just switch to

Suggested change

	doc.createElement('DiV').localName == 'DIV';
	doc.createElement('DiV').localName == 'div';

[ExE-Boss]

The lowercasing of localName only happens in HTML documents:

• https://dom.spec.whatwg.org/#dom-document-createelement

[dperini]

@ExE-Boss
Ok, by reading that I understand that the functionality of localName depends on the document type.

[dperini]

@eps1lon
the commit has been pushed, your suggestion about the test in isHTML() seems adequate.
I also removed two or three .toLowerCase() since they were not necessary any more.
Not much speed gain, but surely an improvement even in nwsapi speed itself.
Curious about the gain we should see in jsdom which is were this started.
Looking forward to comments and more improvements/adjustments.

[eps1lon]

Curious about the gain we should see in jsdom which is were this started.

We had pretty big gains in @testing-library/react in getComputedStyle heavy methods. We're now caching tagName (used by nodeName) in jsdom which lead to up to 40% reduced runtime. Caching tagName and nwsapi using localName are basically equivalent. jsdom/jsdom#3008 has more context (including a benchmark repo).

@eps1lon the commit has been pushed,

What commit? I see this PR now has conflicts. Should I resolve these and is there anything else I should be doing?

[dperini]

@eps1lon
sorry for the mess ... I did things as I should have done from the beginning.
Accepted your pull request ... I will add the small difference in another commit.
After so many changes and error, I believe I would better do a git rebase too when all the new commits are in place.

[eps1lon]

No worries. Whatever makes your life easier.