gistfile1.js

function monthsBetween(thisDate, thatDate) {
  if (thisDate > thatDate) {
    return monthsBetween(thatDate, thisDate);
  }

  var number = 0;
  if (thatDate.getFullYear() > thisDate.getFullYear()) {
    number = number + (thatDate.getFullYear() - thisDate.getFullYear() - 1) * 12;
  } else {
    return thatDate.getMonth() - thisDate.getMonth();
  }

  if (thatDate.getMonth() > thisDate.getMonth()) {
    number = number + 12 + thatDate.getMonth() - thisDate.getMonth();
  } else {
    number = number + (12 - thisDate.getMonth()) + thatDate.getMonth();
  }
  return number;
}