Comments on: WebKit gets Native getElementsByClassName

By: Mark Rowe

Mark Rowe — Wed, 23 Jan 2008 03:43:26 +0000

@Jimmi: The Selectors API is similar to what you suggest but has the advantage of currently going through the standardisation process. Nightly builds of WebKit already support the querySelector and querySelectorAll methods that it specifies.

By: Jimmi

Jimmi — Tue, 22 Jan 2008 18:43:44 +0000

If you’re going down this route, why not implement getElementsBySelector?

See here… http://simonwillison.net/2003/Mar/25/getElementsBySelector/

By: randallfarmer

randallfarmer — Thu, 17 Jan 2008 23:37:47 +0000

@Mark Rowe: That is lovely.

By: Mark Rowe

Mark Rowe — Sat, 05 Jan 2008 23:51:12 +0000

@randallfarmer: It is already supported.

By: randallfarmer

randallfarmer — Sat, 05 Jan 2008 23:17:12 +0000

This may be unlikely to happen, but I’d love anyElement.getElementsByClassName (not just document.getElementsByClassName). It seems to be in the HTML5 spec, but it’s not clear whether it’s in WebKit.

One example of where I’d use it it: I’ve got an application with forms for dozens of similar records. Right now I manually search all elements of the active form for a particular classname (for example, “answergroup” or “errlabel”). But it would be lovely if that could be a native lookup (at least in some browsers).

By: David Smith

David Smith — Tue, 25 Dec 2007 02:02:19 +0000

@Dimitri

Yes it does; you can also specify multiple classes to filter by (for example, document.getElementsByClassName(’box red’);).

By: Dimitri Bouniol

Dimitri Bouniol — Mon, 24 Dec 2007 23:31:01 +0000

Does getElementsByClassName return elements that contain the clas specified?
For Example, if i were to do document. getElementsByClassName(”box”), would it return elements whose class is “box red” as well as the ones having only “box”?

By: Maciej Stachowiak

Maciej Stachowiak — Mon, 24 Dec 2007 02:20:49 +0000

WebKit’s XPath implementation (like, I believe, most of the browser-hosted ones) does not compile down to native code or anything like that. Therefore, XPath matching is likely to involve more branches than something specific to class. In addition, we have caches for fetching by id, class and tag name, which XPath would not easily be able to use without a lot of special-casing for certain XPath expressions.

By: Mark Rowe

Mark Rowe — Mon, 24 Dec 2007 01:43:23 +0000

@gcarothers: In my tests the difference is closer to 15xs, which as you mention is still a very large gap. Some quick testing in the Firefox 3 beta shows a similar performance gap compared to the native getElementsByClassName. I would strongly encourage you to file a performance bug report at http://bugs.webkit.org/ about tightening up this aspect of XPath performance.

By: David Smith

David Smith — Sun, 23 Dec 2007 20:45:28 +0000

@richardyork I’m going to give it a shot, at least. We’ll see if I have enough spare time to finish it