For a specific application where you know the value of classes you
can get away with using a regex, but because it's a fragile
implementation, it might still be wise to avoid. (A simple == is
better.) The reason it's fragile, is the regexp would also match the
valid class name "myclass2". You can't just wrap the text string in
"\b" looking for word boundaries, because '-' is valid in class
names, but triggers a "word boundary".
I typed out a handful of other possible optimizations for
hasClassName based on my recollection of how it was implemented.
Then I checked the source, and found these optimizations were all
implemented sometime around the tail end of last year (the old code,
which is what I remembered, was horribly inefficient). Make sure
you're using a recent Prototype version. The core team put a lot of
work into speedup of $$, et al.
... One possible speedup of the current hasClassName code (which _is_
based on a regex), would be to make the groups non-capturing: several
of the js references I have indicate the regex is faster that way.
It may be worth testing.
TAG
On May 28, 2007, at 10:42 AM, [EMAIL PROTECTED] wrote:
>
> Aha, if I change my custom function to use Element.hasClassName(elt,
> 'myclass') instead of elt.className=='myclass' , then it jumps from
> 16ms to ~250ms. This matches $$('div.blah'), which also took
> ~250ms.
>
> So, FWIW, if you don't need Element.hasClassName -- that is, you're
> only dealing with a single class -- it looks like you can score an
> order of magnitude speed improvement by using "if
> elt.className=='myclass'" instead.
>
> Whoa! Hold on... even elt.className.match('myclass') is way faster
> (16ms) than hasClassName. And that takes care of the multiple-
> classname issue, right?
>
> Has anyone done any detailed profiling of hasClassName? Looks like
> improvements in that might speed up IE's $$ significantly.
>
> Altay
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