How to use the astronomia/lib/solstice.december2 function in astronomia

let jde
    switch (this._season) {
      case 'march': {
        jde = solstice.march2(year, earth)
        break
      }
      case 'june': {
        jde = solstice.june2(year, earth)
        break
      }
      case 'september': {
        jde = solstice.september2(year, earth)
        break
      }
      case 'december': {
        jde = solstice.december2(year, earth)
        break
      }
    }

    const str = new julian.Calendar().fromJDE(jde).toDate().toISOString()
    let date
    if (/^[+-]\d{2}:\d{2}?$/.test(this._timezone)) { // for '+08:00' formats
      date = moment(str).utcOffset(this._timezone)
    } else { // for 'Asia/Shanghai' formats
      date = moment(str).tz(this._timezone) // move to timezone
    }

    const floorDate = {
      year: year,
      month: date.month() + 1,
      day: date.date()

newYear (gyear) {
    gyear = Math.trunc(gyear)
    if (this._cache.ny[gyear]) return this._cache.ny[gyear]

    const sue1 = this._cache.sue[gyear - 1] || solstice.december2(gyear - 1, earth)
    const sue2 = this._cache.sue[gyear] || solstice.december2(gyear, earth)
    this._cache.sue[gyear - 1] = sue1
    this._cache.sue[gyear] = sue2

    const m11n = this.previousNewMoon(this.midnight(sue2 + 1))
    const m12 = this.nextNewMoon(this.midnight(sue1 + 1))
    const m13 = this.nextNewMoon(this.midnight(m12 + lunarOffset))
    this.leapSui = Math.round((m11n - m12) / moonphase.meanLunarMonth) === 12
    let ny = m13

    if (this.leapSui && (this.isLeapMonth(m12) || this.isLeapMonth(m13))) {
      ny = this.nextNewMoon(this.midnight(m13 + moonphase.meanLunarMonth / 2))
    }
    this._cache.ny[gyear] = ny
    return ny
  }

newYear (gyear) {
    gyear = Math.trunc(gyear)
    if (this._cache.ny[gyear]) return this._cache.ny[gyear]

    const sue1 = this._cache.sue[gyear - 1] || solstice.december2(gyear - 1, earth)
    const sue2 = this._cache.sue[gyear] || solstice.december2(gyear, earth)
    this._cache.sue[gyear - 1] = sue1
    this._cache.sue[gyear] = sue2

    const m11n = this.previousNewMoon(this.midnight(sue2 + 1))
    const m12 = this.nextNewMoon(this.midnight(sue1 + 1))
    const m13 = this.nextNewMoon(this.midnight(m12 + lunarOffset))
    this.leapSui = Math.round((m11n - m12) / moonphase.meanLunarMonth) === 12
    let ny = m13

    if (this.leapSui && (this.isLeapMonth(m12) || this.isLeapMonth(m13))) {
      ny = this.nextNewMoon(this.midnight(m13 + moonphase.meanLunarMonth / 2))
    }
    this._cache.ny[gyear] = ny
    return ny
  }

value: function newYear(gyear) {
      gyear = Math.trunc(gyear);
      if (this._cache.ny[gyear]) return this._cache.ny[gyear];

      var sue1 = this._cache.sue[gyear - 1] || solstice.december2(gyear - 1, earth);
      var sue2 = this._cache.sue[gyear] || solstice.december2(gyear, earth);
      this._cache.sue[gyear - 1] = sue1;
      this._cache.sue[gyear] = sue2;

      var m11n = this.previousNewMoon(this.midnight(sue2 + 1));
      var m12 = this.nextNewMoon(this.midnight(sue1 + 1));
      var m13 = this.nextNewMoon(this.midnight(m12 + lunarOffset));
      this.leapSui = Math.round((m11n - m12) / moonphase.meanLunarMonth) === 12;
      var ny = m13;

      if (this.leapSui && (this.isLeapMonth(m12) || this.isLeapMonth(m13))) {
        ny = this.nextNewMoon(this.midnight(m13 + moonphase.meanLunarMonth / 2));
      }
      this._cache.ny[gyear] = ny;
      return ny;
    }

value: function newYear(gyear) {
      gyear = Math.trunc(gyear);
      if (this._cache.ny[gyear]) return this._cache.ny[gyear];

      var sue1 = this._cache.sue[gyear - 1] || solstice.december2(gyear - 1, earth);
      var sue2 = this._cache.sue[gyear] || solstice.december2(gyear, earth);
      this._cache.sue[gyear - 1] = sue1;
      this._cache.sue[gyear] = sue2;

      var m11n = this.previousNewMoon(this.midnight(sue2 + 1));
      var m12 = this.nextNewMoon(this.midnight(sue1 + 1));
      var m13 = this.nextNewMoon(this.midnight(m12 + lunarOffset));
      this.leapSui = Math.round((m11n - m12) / moonphase.meanLunarMonth) === 12;
      var ny = m13;

      if (this.leapSui && (this.isLeapMonth(m12) || this.isLeapMonth(m13))) {
        ny = this.nextNewMoon(this.midnight(m13 + moonphase.meanLunarMonth / 2));
      }
      this._cache.ny[gyear] = ny;
      return ny;
    }