How to use the jalaali-js.toGregorian function in jalaali-js

if(tableRowData && index < 7) {
                //remove html tag and trim
                var item = striptags(tableRowData).trim();
                //convert arabic character to persian number

                if(item) {
                  item = persian(item)
                  .arabicChar()
                  .toString();
                }

                //format and convert city creation date to iso format
                if (index === 2) {
                  var cityCreationDate = item.split('/');
                  if(cityCreationDate.length > 1) {
                    var cityCreationDateGregorian = jalaali.toGregorian(parseInt(cityCreationDate[0]), parseInt(cityCreationDate[1]), parseInt(cityCreationDate[2]));
                    cityCreationDateGregorian = new Date(cityCreationDateGregorian.gy, cityCreationDateGregorian.gm, cityCreationDateGregorian.gd);
                    city['city_creation_date_iso'] = cityCreationDateGregorian.toISOString();
                  } else {
                    var cityCreationDateGregorian = jalaali.toGregorian(parseInt(cityCreationDate[0]), 1, 1);
                    cityCreationDateGregorian = new Date(cityCreationDateGregorian.gy, cityCreationDateGregorian.gm, cityCreationDateGregorian.gd);
                    city['city_creation_date_iso'] = cityCreationDateGregorian.toISOString();
                  }
                }

                //create city object based on schema
                city[schema[index]] = item;
              }
            });

if(item) {
                  item = persian(item)
                  .arabicChar()
                  .toString();
                }

                //format and convert city creation date to iso format
                if (index === 2) {
                  var cityCreationDate = item.split('/');
                  if(cityCreationDate.length > 1) {
                    var cityCreationDateGregorian = jalaali.toGregorian(parseInt(cityCreationDate[0]), parseInt(cityCreationDate[1]), parseInt(cityCreationDate[2]));
                    cityCreationDateGregorian = new Date(cityCreationDateGregorian.gy, cityCreationDateGregorian.gm, cityCreationDateGregorian.gd);
                    city['city_creation_date_iso'] = cityCreationDateGregorian.toISOString();
                  } else {
                    var cityCreationDateGregorian = jalaali.toGregorian(parseInt(cityCreationDate[0]), 1, 1);
                    cityCreationDateGregorian = new Date(cityCreationDateGregorian.gy, cityCreationDateGregorian.gm, cityCreationDateGregorian.gd);
                    city['city_creation_date_iso'] = cityCreationDateGregorian.toISOString();
                  }
                }

                //create city object based on schema
                city[schema[index]] = item;
              }
            });

function toGregorian(jy, jm, jd) {
  var g = jalaali.toGregorian(jy, jm + 1, jd)
  g.gm -= 1
  return g
}

const getMonthFirstWeekday = date => {
    const gregorianFirstDay = isGregorian
      ? { gy: date.year, gm: date.month, gd: 1 }
      : jalaali.toGregorian(date.year, date.month, 1);
    const gregorianDate = new Date(
      gregorianFirstDay.gy,
      gregorianFirstDay.gm - 1,
      gregorianFirstDay.gd,
    );
    const weekday = gregorianDate.getDay();
    if (isGregorian) return weekday;
    return weekday < 6 ? weekday + 1 : 0;
  };

const toNativeDate = date => {
    if (isGregorian) return new Date(date.year, date.month - 1, date.day);
    const gregorian = jalaali.toGregorian(...toExtendedDay(date));
    return new Date(gregorian.gy, gregorian.gm - 1, gregorian.gd);
  };