validating momentjs date in a function

I need to integrate error handling within this function. It should throw an error when the initialDueDate and/or the interval param is invalid. Any suggestions?

   function calculateNextDueDate(initialDueDate, intervalCode) {
      if(moment().diff(initialDueDate) < 0)
        return initialDueDate;
          return calculateNextDueDate(initialDueDate.add(INTERVAL[intervalCode]), intervalCode);
    }

via Shirish Dali