luhn check for jQuery-Validation-Engine

luhnCheck.js

_creditCard: function(field, rules, i, options) {
    var valid = false, cardNumber = field.val().replace(/ +/g, '').replace(/-+/g, '');    

    var numDigits = cardNumber.length;
    if (numDigits >= 14 && numDigits <= 16 && parseInt(cardNumber) > 0) {

        var sum = 0, i = numDigits - 1, pos = 1, digit, luhn = new String();
        do {
            digit = parseInt(cardNumber.charAt(i));
            luhn += (pos++ % 2 == 0) ? digit * 2 : digit;
        } while (--i >= 0)

        for (i = 0; i < luhn.length; i++) {
            sum += parseInt(luhn.charAt(i));
        }
        valid = sum % 10 == 0;
    } 
    if (!valid) return options.allrules.creditCard.alertText;
}

Thanks, Peter--this helped! I rewrote it slightly to be a bit more straightforward (removed the inline variable declarations, changed the do-while loop to a for loop, etc.). Also made it a normal function declaration so you can use as class="validate[funcCall[validateCreditCard]]".

https://gist.github.com/1724921