I have recently completely redid all of jData to make a much securer version. I have also dropped the HTTP query parameter support due to most new advanced browsers support postMessage & localStorage (except Opera, which seems to currently only support postMessage).
The old version wasn’t practical due to having no security system that asked the user if they allowed an action, and the messages were just eval()’d right away. The new version features a much more reliable trust sytem that asks the user for confirmation before anything is set by an untrusted host. Getting data has no restrictions, though, like always. Only setting and removing data and requesting to become a trusted host prompt for user confirmation.
The jDataQuery() snippet I made is now obsolete (but still works as long as you make valid JSON requests that comply with the jData API Reference), and is replaced by JIL, an interface library for jData I also made today.