Return Current Season According to Equinoxes/Solstices

gistfile1.js

function getSeason (dateString) { // format "mm/dd/yy"
  var d = typeof(dateString) == "undefined" ? new Date() : new Date(dateString), // use today if nothing is passed in
      month = d.getMonth()+1,
      day = d.getDate(),
      seasonCode = month+(day/100); // mm.dd
      
        if (seasonCode < 3.21) { return "Winter"}
  else  if (seasonCode < 6.21) { return "Spring"}
  else  if (seasonCode < 9.22) { return "Summer"}
  else  if (seasonCode < 12.21) { return "Fall"}
  else  if (seasonCode >= 12.21) { return "Winter"}
}