var HuidigJaar = "2010";

function CheckForm()
{
    valid=true;

if (form1.requiredOnd.selectedIndex == 0 ){alert ( "Kies Jongen of Meisje!" );valid = false;}
if (form1.requiredNaam.value.length < 2){alert ( "Vul een naam in!" );form1.requiredNaam.focus();valid = false;}
if (form1.requiredOnd.selectedIndex > 0 && form1.requiredNaam.value.length >= 2) {alert ( "Hartelijk dank voor je bijdrage!" );refresh();valid = false;}
  return valid;

}

function isValidDate(dateStr) {

// Checks for the following valid date formats:
// MM/DD/YY   MM/DD/YYYY   MM-DD-YY   MM-DD-YYYY

var datePat = /^(\d{1,2})(\/|-)(\d{1,2})\2(\d{4})$/; // requires 4 digit year

var matchArray = dateStr.match(datePat); // is the format ok?
if (matchArray == null) {
alert("Datum is niet in het juiste formaat")
return false;
}
month = matchArray[1]; // parse date into variables
day = matchArray[3];
year = matchArray[4];
if (month < 1 || month > 12) { // check month range
alert("Maand getal tussen 1 and 12.");
return false;
}
if (day < 1 || day > 31) {
alert("Dag getal tussen 1 and 31.");
return false;
}
if ((month==4 || month==6 || month==9 || month==11) && day==31) {
alert("Maand "+month+" heeft geen 31 dagen!")
return false;
}
if (month == 2) { // check for february 29th
var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
if (day>29 || (day==29 && !isleap)) {
alert("Februari " + year + " heeft geen " + day + " dagen!");
return false;
   }
}
return true;
}

function dispDate(dateObj) {
month = dateObj.getMonth()+1;
month = (month < 10) ? "0" + month : month;

day   = dateObj.getDate();
day = (day < 10) ? "0" + day : day;

year  = dateObj.getYear();
if (year < 2000) year += 1900;

return (month + "/" + day + "/" + year);
}

function pregnancyCalc(pregform) {
menstrual = new Date(); // creates new date objects
ovulation = new Date();
duedate = new Date();
today = new Date();
cycle = 0, luteal = 0; // sets variables to invalid state ==> 0

if (isValidDate(pregform.menstrual.value)) { // Validates menstual date 
menstrualinput = new Date(pregform.menstrual.value);
menstrual.setTime(menstrualinput.getTime())
}
else return false; // otherwise exits

cycle = (pregform.cycle.value == "" ? 28 : pregform.cycle.value); // defaults to 28
// validates cycle range, from 22 to 45
if (pregform.cycle.value != "" && (pregform.cycle.value < 22 || pregform.cycle.value > 45)) {
alert("De periode is te kort of te lang voor \n"
+ "een nauwgezette berekening!  www.voornamen.com gebruikt, \n"
+ "om berekening te voltooien, de door u ingevulde waarde. ");
}

luteal = (pregform.luteal.value == "" ? 14 : pregform.luteal.value); // defaults to 14
// validates luteal range, from 9 to 16
if (pregform.luteal.value != "" && (pregform.luteal.value < 9 || pregform.luteal.value > 16)) {
alert("De periode is te kort of te lang voor \n"
+ "een nauwgezette berekening!  www.voornamen.com gebruikt, \n"
+ "om berekening te voltooien, de door u ingevulde waarde. ");
}

// sets ovulation date to menstrual date + cycle days - luteal days
// the '*86400000' is necessary because date objects track time
// in milliseconds;  86400000 milliseconds equals one day
ovulation.setTime(menstrual.getTime() + (cycle*86400000) - (luteal*86400000));
pregform.conception.value = dispDate(ovulation);

// sets due date to ovulation date plus 266 days
duedate.setTime(ovulation.getTime() + 266*86400000);
pregform.duedate.value = dispDate(duedate);

// sets fetal age to 14 + 266 (pregnancy time) - time left
var fetalage = 14 + 266 - ((duedate - today) / 86400000);
weeks = parseInt(fetalage / 7); // sets weeks to whole number of weeks
days = Math.floor(fetalage % 7); // sets days to the whole number remainder

// fetal age message, automatically includes 's' on week and day if necessary
fetalage = weeks + " we" + (weeks > 1 ? "ken" : "")+(weeks < 2 ? "ek" : "") + " en " + days + " da" +(days > 1 ? "gen" : "")+(days < 2 ? "g" : "");
pregform.fetalage.value = fetalage;

return false; // form should never submit, returns false
}

function MaandSelectie() 
{
   months = new Array();
   months[0]="layer1";
   months[1]="layer2";
   months[2]="layer3";
   months[3]="layer4";
   months[4]="layer5";
   months[5]="layer6";
   months[6]="layer7";
   months[7]="layer8";
   months[8]="layer9";
   months[9]="layer10";
   months[10]="layer11";
   months[11]="layer12";

  today=new Date();
   thisday = today.getDay();
   thismonth = today.getMonth();
   layer=months[thismonth];	

   document.getElementById(layer).style.visibility='visible';
}

function MJan()
{
document.getElementById('layer1').style.visibility='visible';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MFeb()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='visible';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MMrt()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='visible';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MApr()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='visible';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MMei()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='visible';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MJun()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='visible';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MJul()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='visible';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MAug()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='visible';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MSep()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='visible';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MOkt()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='visible';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='hidden';
}

function MNov()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='visible';
document.getElementById('layer12').style.visibility='hidden';
}

function MDec()
{
document.getElementById('layer1').style.visibility='hidden';
document.getElementById('layer2').style.visibility='hidden';
document.getElementById('layer3').style.visibility='hidden';
document.getElementById('layer4').style.visibility='hidden';
document.getElementById('layer5').style.visibility='hidden';
document.getElementById('layer6').style.visibility='hidden';
document.getElementById('layer7').style.visibility='hidden';
document.getElementById('layer8').style.visibility='hidden';
document.getElementById('layer9').style.visibility='hidden';
document.getElementById('layer10').style.visibility='hidden';
document.getElementById('layer11').style.visibility='hidden';
document.getElementById('layer12').style.visibility='visible';
}