Verify a date in JavaScript - asp.net

Question

I need to do user validation of a date field, it should be in the format yyyyMMdd and should not be more than one year in the future. How would I go about doing this? Currently I only have a crude regexp which is insufficient.
function VerifyDate(source, args)
{
var regexp = /^([1-2]{1}[0-9]{1})\d{2}([0][1-9]|[1][0-2])([0][1-9]|[1-2][0-9]|[3][0-1])$/
var result = args.Value.match(regexp);
if(result) {
args.IsValid = true;
} else {
args.IsValid = false;
}
}

Answer 1

Take the regex to check the format only. You can stay simple:
^(\d{4})(\d{2})(\d{2})$
Then parse the date and check the range:
function VerifyDate(source, args)
{
args.IsValid = false;
var regexp = /^(\d{4})(\d{2})(\d{2})$/;
var daysInMonth = function (y, m) {return 32-new Date(y, m, 32).getDate(); };
var ma = regexp.exec(args.Value);
if (ma && ma.length == 4 && ma[2] < 12 && ma[3] <= daysInMonth(ma[1], ma[2]))
{
var diff = new Date(ma[1], ma[2], ma[3]) - new Date();
args.IsValid = diff < 31536000000; // one year = 1000ms*60*60*24*365
}
}

Answer 2

new Date() don't throw an exception if month or day is out of range. It uses the internal MakeDay to calculate a date (see ECMAScript Language Specification section 15.9.3.1 and 15.9.1.13). To make sure that the date is valid in the function below, the input is converted to integers who is converted to a date, and then the parts of the date are compared to the integers.
Since date uses MakeDay, the calculation of maxDate works even if now is the leep day (xxxx0229 will be yyyy0301 where yyyy=xxxx+1)
function verifyDate(args)
{
var result=false,
match = args.Value.match(/^(\d{4})(\d{2})(\d{2})$/);
if (match && match.length === 4)
{
var year = parseInt(match[1],10),
month =parseInt(match[2],10) -1, // 0 = January
day = parseInt(match[3],10),
testDate= new Date(year,month,day),
now = new Date(),
maxDate = new Date(now.getFullYear() + 1, now.getMonth(), now. getDate()),
minDate = new Date(1800,0,1),
result = (
testDate.getFullYear() === year &&
testDate.getMonth() === month &&
testDate.getDate() === day &&
testDate >= minDate &&
testDate <= maxDate
);
}
args.IsValue = result;
return result;
}

Answer 3

The solution I finally went with is a combination of your answers, I used datejs which seems pretty nice. Here is my final validation function. For some reason the month seems to use a 0 based index so that's why it says -1 in the .set().
function VerifyDate(source, args)
{
args.IsValid = false;
var regexp = /^(\d{4})(\d{2})(\d{2})$/;
var m = regexp.exec(args.Value);
if (m && m.length == 4) {
try {
var result = Date.today().set({ year: Number(m[1]), month: Number(m[2]-1), day: Number(m[3]) });
if (result < Date.today().add({ years: 1 })) {
args.IsValid = true;
}
}
catch (ex) {
}
}
}