JavaScript / Rhino: Can I use a regular expression in an E4X query to select certain nodes only?

Question

I'm working on Rhino (Mirth), and I've got to process / parse an XML with the following structure:

<root>
<row>
<foo-1 />
<foo-2 />
<foo-3 />
<foo-4 />
...
<bar-1 />
<bar-2 />
<bar-3 />
<bar-4 />
...
<something-else-1 />
<something-else-2 />
</row>
</root>

I want to get all the "foo" nodes only, avoiding the use of loops if possible. I've been trying somenthing like:

xml.row.(new RegExp("foo[1-4]").test()))

and a few variations of the same line, but it does not seem to work. Is there any E4X syntax / method to get this done?? I've been googling for a while, and i've read the ECMAS documentation, but i can't get this done.

Thanks in advance!

Answer 1

xml.row.*.( /foo-[1-4]/.test(function::localName()) )

Answer 2

Btw, you can do it without regex too.

var foo = xml.row.*.(String(localName()).indexOf("foo-") == 0);
alert(foo.length() + "\n" + foo.toXMLString());

Answer 3

This is how you should be able to do it, but it doesn't work in Rhino:

xml.row.*.( /foo-[1-4]/.test(name()) ) // or localName()

For now, as far as I know, you will need to use a loop.

If you don't mind getting an array instead of an XMLList, and your version of Rhino supports array comprehensions, you could use this:

[foo for each (foo in xml.row.*) if (/foo-[1-4]/.test(foo.name()))]

It still uses a loop, but it's a little more declarative at least.

Edit: Like Elijah Grey mentioned in the comments, if you are using namespaces you would need to either call localName() or name().localName. Of course, to be completely correct, you would need to compare the namespace URI as well.

Also, apparently, SpiderMonkey (Firefox) requires you to prefix function calls with function:: in filter predicates, so the filter would look like this:

/foo-[1-4]/.test(function::name()) // or function::localName()

Typically, Rhino follows what SpiderMonkey does, so when it supports function calls in predicates, you may need the function:: prefix.

Answer 4

A bug has been opened against Rhino relating to this behavior. If you feel brave, you may want to try out the patch proposed by Martin Blom, as noted in the comments to the bug.