Hello @fraxzi
Try this approach:
procedure TMainForm.UniFormCreate(Sender: TObject);
begin
UniFieldSet1.JSInterface.JSAddElEvent('scroll', 'scrollable', [''], UniFieldSet2.JSName +'.scrollable.scrollTo(this.component.scrollable.getPosition().x, this.component.scrollable.getPosition().y)');
UniFieldSet2.JSInterface.JSAddElEvent('scroll', 'scrollable', [''], UniFieldSet1.JSName +'.scrollable.scrollTo(this.component.scrollable.getPosition().x, this.component.scrollable.getPosition().y)');
end;