How to use JavaScript to determine whether the date of entry is legal

javascript| Date

How to use JavaScript to determine whether the date of entry is legal

function Isvalidyear (psyear)
{
var syear = new String (psyear);

if (psyear==null)
{
return false;
}

if (isNaN (psyear) ==true)
{
return false;
}

if (Syear = "")
{
return true;
}

if (Syear.match (/[^0-9]/g)!=null)
{
return false;
}

var nyear = parseint (Syear, 10);

if ((Nyear < 0) | | (9999 < nyear))
{
return false;
}

return true;
}

function Isvalidmonth (psmonth)
{
var smonth = new String (psmonth);

if (psmonth==null)
{
return false;
}

if (isNaN (psmonth) ==true)
{
return false;
}

if (Smonth = "")
{
return true;
}

if (Smonth.match (/[^0-9]/g)!=null)
{
return false;
}

var nmonth = parseint (smonth,10);

if ((Nmonth < 0) | | (< Nmonth))
{
return false;
}

return true;
}

function Isvalidday (psday)
{
var sday = new String (psday);

if (psday==null)
{
return false;
}

if (isNaN (psday) ==true)
{
return false;
}

if (Sday = "")
{
return true;
}

if (Sday.match (/[^0-9]/g)!=null)
{
return false;
}

var nday = parseint (Psday, 10);

if ((Nday < 0) | | (< Nday))
{
return false;
}

return true;
}

function Isvaliddate (psyear, Psmonth, Psday)
{
if (psyear==null | | psmonth==null | | psday==null)
{
return false;
}

var syear = new String (psyear);
var smonth = new String (psmonth);
var sday = new String (psday);

if (Isvalidyear (syear) ==false)
{
return false;
}

if (Isvalidmonth (smonth) ==false)
{
return false;
}

if (Isvalidday (sday) ==false)
{
return false;
}

var nyear = parseint (Syear, 10);
var nmonth = parseint (Smonth, 10);
var nday = parseint (Sday, 10);

if (syear== "" && smonth== "" && sday== "")
{
return true;
}

if (syear== "" | | smonth== "" | | sday== "")
{
return false;
}

if (Nmonth < 1 | | | < nmonth)
{
return false;
}
if (Nday < 1 | | < Nday)
{
return false;
}

if (Nmonth = 2)
{
if ((nyear% 400 = 0) | | (nyear% 4 = 0) && (nyear% 100!= 0))
{
if ((Nday < 1) | | (Nday > 29))
{
return false;
}
}
Else
{
if ((Nday < 1) | | (Nday > 28))
{
return false;
}
}
}
else if ((Nmonth = 1) | |
(Nmonth = 3) | |
(Nmonth = 5) | |
(Nmonth = 7) | |
(Nmonth = 8) | |
(Nmonth = 10) | |
(Nmonth = 12))
{
if ((Nday < 1) | | (< Nday))
{
return false;
}
}
Else
{
if ((Nday < 1) | | (< Nday))
{
return false;
}
}

return true;
}