The QScriptValue(QScriptEngine*, ...) constructors are obsoleted in favor of the more convenient constructors that take only a value; however, using the convenience constructors comes at a performance cost, since QScriptValue internally has to do more work in lazily binding the value to an engine later.
Either this performance issue should be fixed, or the constructors should be un-obsoleted, and the documentation should mention that these constructors are less convenient but give better performance.