You just need the TabletOS QNX-native toolchain (not cross-compiler) and a text editor (eg. docs to go?) and a shell. It's conceivable some masochist at QNX has experimented with such an abomination. It's doubtful they lived long enough to tell about it.
A JavaScript runner would be fairly trivial to build. If I'm not mistaken there is a JS debugger built into the browser.
Look for JS Console in App World for a JavaScript runner and Basic for BlackBerry PlayBook for a basic BASIC interpreter. There are some others similar toy-like proofs of concept - fun but not at all practical for serious development.
I haven't counted the number of lines of code in What's up but there are over 50 files. Many of the modules were e ported from a Java project that I was working on, using the copy-paste-rewrite technique. Remember that while spelling mistakes are annoying when you're writing an email, spelling, punctuation and capitalization must be absolutely flawless when you're programming. As good as PB is, I sometimes have a tough time writing posts to this forum. Personally, I could never see myself writing and debugging 20,000 lines of code on the device.