TWebClientdataSet - identifier not found "TAggregateField"

I can add Aggragates at designtime, but the compiler complains. Why?

tx Bernd

The design-time dataset (offered by VCL TClientDataSet) has it but the pas2js dataset not.
It's something we can sadly not remove from the design-time as long as we descend for the design-time from TClientDataSet