code: @Override
      public boolean has(int index, Scriptable start)
      {
          if (externalData != null) {
              return (index < externalData.getArrayLength());
          }
          return null != slotMap.query(null, index);
      }
docs: Returns true if the property index is defined.
  
  @param index the numeric index for the property
  @param start the object in which the lookup began
  @return true if and only if the property was found in the object