code: public void setTypeCode(int typeCode) {
      if (typeCode <= 0 || typeCode >= JSBaseTypes.baseTypes.length)
        throw new IllegalArgumentException("TypeCode=" + typeCode);
      this.typeCode = typeCode;
      baseType = JSBaseTypes.baseTypes[typeCode];
    }
docs: Set the typeCode for the type.  Doing this automatically sets all the other type
  information implied by the type.