Entry

How to calculate an age exactly from the given date of birth

Mar 5th, 2000 20:28
Hiroto Sekine, https://buttons.ihug.co.nz/all/enrolmentE.htm

Here is a sample source code to get age exactly. This function is 
useful for such an enrokment form, members application form which 
requires user's age. You can try this function using your birthday at 
above site. Please mind that the implemented source code is alittle bit 
different from the code below.
function makeDaysOfMonth(){
  var i = 0;
  this[i++] = 0; // dummy
  this[i++] = 31;
  this[i++] = 29;
  this[i++] = 31;
  this[i++] = 30;
  this[i++] = 31;
  this[i++] = 30;
  this[i++] = 31;
  this[i++] = 31;
  this[i++] = 30;
  this[i++] = 31;
  this[i++] = 30;
  this[i  ] = 31;
  this.length = i;
}
function calcAge(dd, mm, yy){
  var t, mon, day, year, DD, MM, YY, age;
  var MTB = new makeDaysOfMonth();
  YY   = parseInt(yy);	// year of birth (4 digits)
  MM   = parseInt(mm);	// month of birth (1-12)
  DD   = parseInt(dd);	// date of birth (1-31)
  if (MTB[MM] < DD || DD < 1) return -1;
  t    = new Date();	// get current date
  year = t.getFullYear();	// get year of current
  mon  = t.getMonth() + 1;	// get month of current
  day  = t.getDate();	// get date of current
  if (MM == 2 && DD == 29){	// check leap year
    if (!(((YY % 4 == 0) && (YY % 100 != 0)) || (YY % 400 == 0))){
      alert("The year " +YY+ " ends at 28th of "+MM+" month\nPlease 
check the date.");
      return -1;
    }
  }
  age = year - YY;
  if ((MM > mon) || (MM == mon && day < DD)) age --;
  return age;
}