See http://doc.trolltech.com/latest/qscriptable.html This API effectively gives a C++ slot access to the this-object and arguments when the slot is invoked from JS. It's most useful for implementing a QObject-based prototype object. It can also be used to implement slots that can take an arbitrary number of arguments (normally the "extra" arguments would be discarded when calling the slot).
Porting QtScript API over JSC C API will not be continued.