getAge.js

getAge = function (birthDate, nowDate) {
  var today, age, mDiff, dDiff;
  today = nowDate || new Date();
  
  age = nowDate.getFullYear() - birthDate.getFullYear();
  mDiff = nowDate.getMonth() - birthDate.getMonth();
  dDiff = nowDate.getDate() - birthDate.getDate();
  
  if (mDiff < 0 || (mDiff === 0 && dDiff < 0)) {
    age -= 1;
  }
  
  return age
}