getHoroscopeSign.js

const signs = {
  1: day => day <= 19 ? 'capricorn' : 'aquarius',
  2: day => day <= 18 ? 'aquarius' : 'pisces',
  3: day => day <= 20 ? 'pisces' : 'aries',
  4: day => day <= 19 ? 'aries' : 'taurus',
  5: day => day <= 20 ? 'taurus' : 'gemini',
  6: day => day <= 20 ? 'gemini' : 'cancer',
  7: day => day <= 22 ? 'cancer' : 'leo',
  8: day => day <= 22 ? 'leo' : 'virgo',
  9: day => day <= 22 ? 'virgo' : 'libra',
  10: day => day <= 22 ? 'libra' : 'scorpio',
  11: day => day <= 21 ? 'scorpio' : 'sagittarius',
  12: day => day <= 21 ? 'sagittarius' : 'capricorn',
}

function getHoroscopeSign(day, month) {
  return signs[month](day);
};

console.log(getHoroscopeSign(28, 5));