Hi, Boris-
Boris Zbarsky wrote (on 3/28/08 1:41 PM):
Doug Schepers wrote:
Speaking as an author of many SVG Webapps and a contributor to
several SVG script libs, knowing the number of child elements is a
really common need; index-based access is less needed, and can be
effected by other means.
I would just like to point out, from my perspective as an implementor,
that implementing this as a nodelist would have taken all of 15 minutes
of programming time. Implementing the specification as written, while
having acceptable performance on traversal, will take a good bit more
work, and either a lot more complexity or additional space used by every
single Element in the DOM.
I realize that this is due to the fact that I'm working with an
implementation that already has a generic NodeList implementation...
Nevertheless, the issue is there.
I have the feeling that I already mentioned this in the past, so I
assume it's been considered in making the decision that the
linked-list-only API is the one to use, but I wanted to mention it in
case I hadn't before.
Yes, you did, and I pointed out that not all implementations have
existing nodeList implementations, and that one of the design goals was
to work with mobile UAs that don't already support nodeList (live or
static). [1]
After some discussion in the same thread, I then put the direct question
to the list as to whether or not to include a nodeList [2], and the only
reply I got was from Maciej, in support of removing it. [3]
This was last April, and the spec has not changed appreciably since
then, so I assumed the issue was closed, and that you appreciated the
design goal.
P.S. Oddly enough, in typical DOM authoring authors use index-based of
childNodes a _lot_ more than the linked-list accessors.... Has anyone
looked into why?
My guess is that undifferentiated navigation to any node type is simply
not that useful, which is why Element Traversal was made. Also, without
knowing the number of child nodes of the target type, there are some
pre-processing operations that aren't easily done, so again it's less
useful; by the time you bother getting a nodeList to find out the number
of children, you may as well iterate through the list.
Also, it may be that casual authors simply don't know about those
accessors, since looping structures are themselves so widely used.
[1] http://lists.w3.org/Archives/Public/public-webapi/2007Apr/0009.html
[2] http://lists.w3.org/Archives/Public/public-webapi/2007Apr/0012.html
[3] http://lists.w3.org/Archives/Public/public-webapi/2007Apr/0013.html
Regards-
-Doug Schepers
W3C Team Contact, SVG, CDF, and WebAPI
