In my web applications that are served by perl... with static data (eg phone dir with 100 entries), I just run cron task that generates javascript file with javascript data structures and that file is loaded and cached by browsers. I don't even try to go through XMLHttpRequest for JSON -- just plain javascript file that is refreshed lazily. This is quite useful solution -- data in Javascript is available as native data structures in browser... and on server side you have simple perl script to import data from DB and save that javascript file beeing included in web service.