Valide uma data de forma eficaz com qualquer delimitador e ano de 4 dígitos

/* Validate a date from string effectively with
* any delimiter and 4 digit year.

*
@param value The value of the input.
*
@param userFormat The user format with 4 digit year.
* @return bool

*/

function isValidDate (value, userFormat) {

userFormat
= userFormat || 'mm/dd/yyyy'

var delimiter = /[^mdy]/.exec(userFormat)[0]
var theFormat = userFormat.split(delimiter)
var theDate = value.split(delimiter)

function isDate (date, format) {
var m, d, y, i = 0, len = format.length, f
for (i; i < len; i++) {
f
= format[i]
if (/m/.test(f)) m = date[i]
if (/d/.test(f)) d = date[i]
if (/y/.test(f)) y = date[i]
}
return (
m
> 0 && m < 13 &&
y
&& y.length === 4 &&
d
> 0 && d <= (new Date(y, m, 0)).getDate()
)
}

return isDate(theDate, theFormat)

}

// Usage:
// This will return FALSE,
// November doesn't have 31 days
console
.log( isValidDate('dd/mm/yyyy', '31/11/2012') )