iRule Javascript call?

The URI isn't saved for response events. So you could check the URI in HTTP_REQUEST and then set a variable to 1 to track whether to inject the javascript in the response:

when HTTP_REQUEST {

    Check if some URI property is true
   if {[string tolower [HTTP::path]] contains "/foopage/"}{
       Track that we'll inject the js in the response
      set inject_js 1
   } else {
       Track that we won't inject the js in the response
      set inject_js 0
   }
}
when HTTP_RESPONSE {
    Check whether we're injecting the js in the response payload
   if {$inject_js==1}{
       Do it...
   }
}

Also note that it would probably be more efficient to use a stream profile to insert the javascript. See this post for a related example:

http://devcentral.f5.com/Default.aspx?tabid=53&aff=5&aft=1144860&afv=topic&afpgj=1

Aaron