Rails spinoffs - Feb 2007 - questions regarding the use of recursivelyCollect

Some quick background:
I''m developing a portlet to be deployed in Liferay 4.2.1.  They use
prototype as their javascript framework.  One function that is used in
a couple of places is getElementsByClassName.  I have problems with
the use of that function because of its use of getElementsByTag("*").
I even altered getElementsByClassName to take a third argument so as
to replace the call as getElementsByTag(tagName || "*").  That only
offered a moderate performance increase.  Performance is an issue
because my portlet is essentially a 35x900 table, which is
unavoidable.

I am now considering walking the DOM, since getElementsByClassName was
being used to only fetch the 0''th element of the returned array.  If
anyone knows of a quick way to nab the first matching element, please
tell me!  I am new to prototype, but it seems pretty straightforward
to use.  A function like "getFirstElementByClassName" would be
spectacular in this case, especially if it didn''t retrieve all
descendent nodes in the process.

I thought about implementing it myself using prototype''s up/down/
previous/next functions, but as far as I can tell reading the source,
those functions also get all descendents via
recursivelyCollect(previousSibling/nextSibling).

Am I mistaken about how recursivelyCollect works in the above cases?
Will recursivelyCollect(''nextSibling'') dive through all
descendents,
or just those one level deep?


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On Feb 3, 2:53 am,
"jeffrey.da...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org"
<jeffrey.da...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Some quick background:
> I''m developing a portlet to be deployed in Liferay 4.2.1.  They
use
> prototype as their javascript framework.  One function that is used in
> a couple of places is getElementsByClassName.  I have problems with
> the use of that function because of its use of
getElementsByTag("*").
> I even altered getElementsByClassName to take a third argument so as
> to replace the call as getElementsByTag(tagName || "*").  That
only
> offered a moderate performance increase.  Performance is an issue
> because my portlet is essentially a 35x900 table, which is
> unavoidable.
Which version of Prototype?  getElementsByClassName was notoriously
slow in 1.4, however 1.5 offers an XPath fork which is much faster
than DOM methods.

Browsers that don''t support XPath still get a slow method, the
following is 2 to 4 times faster than the non-XPath fork in Prototype
(depending on browser) but is slower than the XPath fork:

/* return first element that matches a particular class name
 * className     - required, a valid class name.
 * parentElement - optional, a DOM element reference.
 *                 If missing, document is used.
 * tagName       - optional, restricts search to only elements
 *                 with that tag name.
 */
function getFirstElementByClassName(className, parentElement,
tagName)
{
  parentElement = parentElement || document;
  var nodes = parentElement.getElementsByTagName(tagName ||
''*'');
  var i=0;
  var classRe = new RegExp("(^|\\s)" + className +
"(\\s|$)");

  while(node = nodes[i++]) {
    if (classRe.test(node.className)){
      return node;
    }
  }
}


--
Rob


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