As described in a previous blog entry, the day-to-day work on the JSC-based back-end for QtScript mainly revolves around getting lots of tiny (TINY!) tests to pass, ensuring that the observed behavior of the C++ API and JS runtime is still compatible. Well, things are starting to add up: The Qt bindings produced by the bindings generator now work with the JSC-based back-end. Oh, and most of the QtScript examples in Qt (examples/script folder) work. So even though there's still API that's missing or misbehaving (mostly exotic stuff, really -- who needs a debugger? ;) ), at least it's possible to get something useful out of it.
The code can be found in the qt-webkit repository, qtscript-jsc-backend branch. Have fun! (If you were planning on doing performance measurements, note that the JIT is disabled for the time being.)