Javascript: Check Date Format in TextBox

function fnIsValidDate(dateStr, format)
{
if (format == null) { format = "MDY"; }
format = format.toUpperCase();
if (format.length != 3) { format = "MDY"; }
if ( (format.indexOf("M") == -1) || (format.indexOf("D") == -1) || (format.indexOf("Y") == -1) ) { format = "MDY"; }
if (format.substring(0, 1) == "Y") { // If the year is first
var reg1 = /^\d{2}(|\/|\.)\d{1,2}\1\d{1,2}$/
var reg2 = /^\d{4}(|\/|\.)\d{1,2}\1\d{1,2}$/
} else if (format.substring(1, 2) == "Y") { // If the year is second
var reg1 = /^\d{1,2}(|\/|\.)\d{2}\1\d{1,2}$/
var reg2 = /^\d{1,2}(|\/|\.)\d{4}\1\d{1,2}$/
} else { // The year must be third
var reg1 = /^\d{1,2}(|\/|\.)\d{1,2}\1\d{2}$/
var reg2 = /^\d{1,2}(|\/|\.)\d{1,2}\1\d{4}$/
}
// If it doesn't conform to the right format (with either a 2 digit year or 4 digit year), fail
if ( (reg1.test(dateStr) == false) && (reg2.test(dateStr) == false) ) { return false; }
var parts = dateStr.split(RegExp.$1); // Split into 3 parts based on what the divider was
// Check to see if the 3 parts end up making a valid date
if (format.substring(0, 1) == "M") { var mm = parts[0]; } else if (format.substring(1, 2) == "M") { var mm = parts[1]; } else { var mm = parts[2]; }
if (format.substring(0, 1) == "D") { var dd = parts[0]; } else if (format.substring(1, 2) == "D") { var dd = parts[1]; } else { var dd = parts[2]; }
if (format.substring(0, 1) == "Y") { var yy = parts[0]; } else if (format.substring(1, 2) == "Y") { var yy = parts[1]; } else { var yy = parts[2]; }
if (parseFloat(yy) <= 50) { yy = (parseFloat(yy) + 2000).toString(); }
if (parseFloat(yy) <= 99) { yy = (parseFloat(yy) + 1900).toString(); }
var dt = new Date(parseFloat(yy), parseFloat(mm)-1, parseFloat(dd), 0, 0, 0, 0);
if (parseFloat(dd) != dt.getDate()) { return false; }
if (parseFloat(mm)-1 != dt.getMonth()) { return false; }
return true;
}

Usage

var oDate = document.getElementById(Temp + "txtLimitDisplay").value.trim();
//oDate.value = trim(oDate.value);
if(oDate != '' && !fnIsValidDate(oDate, 'MDY'))
{
alert('Please enter date in \' MM\/DD\/YYYY \' format.')
document.getElementById(Temp + "txtLimitDisplay").focus();
return false;
}

var arr;
if(document.getElementById(Temp + "txtLimitDisplay").value!=null)
arr=document.getElementById(Temp + "txtLimitDisplay").value.split('/')



var SelectedDate=new Date()
SelectedDate.setFullYear(arr[2],arr[0]-1,arr[1])
SelectedDate.setHours(00,00,00,00);


var CurrentDate=new Date();

CurrentDate.setFullYear(CurrentDate.getFullYear(),CurrentDate.getMonth(),CurrentDate.getDate());
CurrentDate.setHours(00,00,00,00);
// alert(SelectedDate);
// alert(CurrentDate);
var intMonth=arr[0];

if(intMonth.length > 2)
{
alert("Please enter date in \' MM\/DD\/YYYY \' format.");
document.getElementById(Temp + "txtLimitDisplay").focus();
return false;
}


if(SelectedDate <= CurrentDate)
{
alert("Expiry Date should be greater than current date.");
document.getElementById(Temp + "txtLimitDisplay").focus();
return false;
}