Moonphase.js

  // 0 => New Moon
  // 1 => Waxing Crescent Moon
  // 2 => Quarter Moon
  // 3 => Waxing Gibbous Moon
  // 4 => Full Moon
  // 5 => Waning Gibbous Moon
  // 6 => Last Quarter Moon
  // 7 => Waning Crescent Moon
  const moonNames = ['New Moon', 'Waxing Crescent Moon', 'Quarter Moon', 'Waxing Gibbous Moon', 'Full Moon', 'Waning Gibbous Moon', 'Last Quarter Moon', 'Waning Crescent Moon'];

function getMoonPhase(year, month, day) {
      var c = e = jd = b = 0;

      if (month < 3) {
        year--;
        month += 12;
      }

      ++month;

      c = 365.25 * year;

      e = 30.6 * month;

      jd = c + e + day - 694039.09; //jd is total days elapsed

      jd /= 29.5305882; //divide by the moon cycle

      b = parseInt(jd); //int(jd) -> b, take integer part of jd

      jd -= b; //subtract integer part to leave fractional part of original jd

      b = Math.round(jd * 8); //scale fraction from 0-8 and round

      if (b >= 8) {
        b = 0; //0 and 8 are the same so turn 8 into 0
      }

      return b;
    }

//"Moon Phase: " + moonNames[getMoonPhase(year, month, day)];