How to validate and re-format date inputs (default set to DD-MON-YYYY)

The script is pretty big and I'm reasonably new to Javascript so I'm sure it could be written more efficiently. I looked for a script that was reasonably exhaustive as my users are impatient and don't want to worry about how they enter their dates, couldn't find exactly what I wanted so bastardised a few scripts and came up with this

It'll take pretty much any input (1.1.4, 24*DEC*2001, 010104 etc) and validate it before returning DD-MON-YYYY (I used it in an Oracle form). It should be easy to change this to whatever output you're after.

Hope it's useful...

Joe.

function isDateorNull(theElement, theElementName) {
var CorrectDate;
var SplitDate;
var thisDay;
var thisMonth;
var thisYear;
var inpDate = theElement.value;
var DayArray = new Array(31,28,31,30,31,30,31,31,30,31,30,31);
var MonthArray = new Array("JAN","FEB","MAR","APR","MAY","JUN","JUL","AUG","SEP","OCT","NOV","DEC");
var CockUp = 0;

// kill if nothing there
if (inpDate.length == 0 ) return true;

// numerical dates first for DDMMYYYY OR DDMMYY
if (/^[0-9]{3}$/.test(inpDate.substr(1,3))) {

if (/^[0-9]{8}/.test(inpDate)) {thisDay = inpDate.substr(0,2); thisMonth = inpDate.substr(2,2); thisYear = inpDate.substr(4,4);}
else if (/^[0-9]{6}/.test(inpDate)) {thisDay = inpDate.substr(0,2); thisMonth = inpDate.substr(2,2); thisYear = inpDate.substr(4,2);}
else {CockUp = 1;}
}
// now alpha numeric dates for DDMONYYYY, DMONYYYY, DDMONYY, DMONYY, DDMONY, DMONY or MONYY
else if (/^[a-zA-Z|0-9]{3}$/.test(inpDate.substr(1,3))) {

if (/^[0-9|a-zA-Z]{9}/.test(inpDate)) {thisDay = inpDate.substr(0,2); thisMonth = inpDate.substr(2,3).toUpperCase(); thisYear = inpDate.substr(5,4);}
else if (/^[0-9|a-zA-Z]{8}/.test(inpDate)) {thisDay = inpDate.substr(0,1); thisMonth = inpDate.substr(1,3).toUpperCase(); thisYear = inpDate.substr(4,4);}
else if (/^[0-9|a-zA-Z]{7}/.test(inpDate)) {thisDay = inpDate.substr(0,2); thisMonth = inpDate.substr(2,3).toUpperCase(); thisYear = inpDate.substr(5,2);}
else if (/^[0-9|a-zA-Z]{6}/.test(inpDate)) {if (/^[a-zA-Z]{1}/.test(inpDate.substr(1,1))) {thisDay = inpDate.substr(0,1); thisMonth = inpDate.substr(1,3).toUpperCase(); thisYear = inpDate.substr(4,2);}
else {thisDay = inpDate.substr(0,2); thisMonth = inpDate.substr(2,3).toUpperCase(); thisYear = inpDate.substr(3,2);}}
else {CockUp = 1;}

}
// lastly pick up every conceivable special character or kick out with error
else {
if (/-/.test(inpDate)) {SplitDate = inpDate.split("-");}
else if (/\//.test(inpDate)) {SplitDate = inpDate.split("/");}
else if (/\./.test(inpDate)) {SplitDate = inpDate.split(".");}
else if (/,/.test(inpDate)) {SplitDate = inpDate.split(",");}
else if (/\;/.test(inpDate)) {SplitDate = inpDate.split(";");}
else if (/\:/.test(inpDate)) {SplitDate = inpDate.split(":");}
else if (/\*/.test(inpDate)) {SplitDate = inpDate.split("*");}
else if (/_/.test(inpDate)) {SplitDate = inpDate.split("_");}
else if (/%/.test(inpDate)) {SplitDate = inpDate.split("%");}
else {CockUp = 1;}
thisDay = SplitDate[0];
thisMonth = SplitDate[1].toUpperCase();
thisYear = SplitDate[2];
}

// request reinput data if nonexistent
if (!thisYear) {CockUp = 1;}
if (!thisMonth) {CockUp = 1;}
if (!thisDay) {CockUp = 1;}

// kick out any errors before we do any formatting etc
if (CockUp == 1) {
alert("Your input date format is incorrect or contains invalid characters - please try again using DD-MON-YYYY");
theElement.focus();
return false;
}

// change from numeric to alpha-numeric
if (/^[0-9]{1}$/.test(thisMonth.substr(0,1))) {
switch (thisMonth) {
case "01" : case "1" : thisMonth = 'JAN'; break;
case "02" : case "2" : thisMonth = 'FEB'; break;
case "03" : case "3" : thisMonth = 'MAR'; break;
case "04" : case "4" : thisMonth = 'APR'; break;
case "05" : case "5" : thisMonth = 'MAY'; break;
case "06" : case "6" : thisMonth = 'JUN'; break;
case "07" : case "7" : thisMonth = 'JUL'; break;
case "08" : case "8" : thisMonth = 'AUG'; break;
case "09" : case "9" : thisMonth = 'SEP'; break;
case "10" : thisMonth = 'OCT'; break;
case "11" : thisMonth = 'NOV'; break;
case "12" : thisMonth = 'DEC'; break;
default : alert("Your input month is incorrect, it should be between 1 and 12"); theElement.focus(); return false;
}
}

// sort variable lengths out and build date
if (thisDay.length == 1) {thisDay = "0" + thisDay;}
if (thisYear.length == 1) {thisYear = "200" + thisYear;}
if (thisYear.length == 2) {if (thisYear >= 50) {thisYear = "19" + thisYear; } else {thisYear = "20" + thisYear;}}
CorrectDate = thisDay + "-" + thisMonth + "-" + thisYear;

// Check alpha-numeric Valid Month
var filter=/JAN|FEB|MAR|APR|MAY|JUN|JUL|AUG|SEP|OCT|NOV|DEC/;
if (! filter.test(thisMonth)) {
alert("Please enter a Correct Month");
theElement.focus();
return false;
}

// Check For Leap Year
N=thisYear;
if ( ( N%4==0 && N%100 !=0 ) || ( N%400==0 ) ) {
DayArray[1]=29;
}

// check for correct days in month
for(var ctr=0; ctr<=11; ctr++){
if (MonthArray[ctr]==thisMonth) {
if (thisDay<= DayArray[ctr] && thisDay >0 ) {
CockUp = 0;
} else {
alert("Your day input is incorrect for the month in question");
theElement.focus();
return false;
CockUp = 1;
}
}
if (CockUp == 0) {
theElement.value = CorrectDate;
}
}
}