SplitAt method doesn't exist in Professional Version

I have received trial professional version. Now all deactivated functions work, but I have a problem with function “SplitAt()”. In console I receive a message, that Object has no method SplitAt(). Could you explain me why it’s still not in Professional Version? For our company this method is very important, that’s why we have selected dhtmlx library.

Please, provide a sample of your code with the init of your grid to provide a proper solution.