function isValidCreditCard(type, ccnum) {
if (type == "Visa") {
// Visa: length 16, prefix 4, dashes optional.
var re = /^4\d{3}-?\d{4}-?\d{4}-?\d{4}$/;
} else if (type == "MC") {
// Mastercard: length 16, prefix 51-55, dashes optional.
var re = /^5[1-5]\d{2}-?\d{4}-?\d{4}-?\d{4}$/;
} else if (type == "Disc") {
// Discover: length 16, prefix 6011, dashes optional.
var re = /^6011-?\d{4}-?\d{4}-?\d{4}$/;
} else if (type == "AmEx") {
// American Express: length 15, prefix 34 or 37.
var re = /^3[4,7]\d{13}$/;
} else if (type == "Diners") {
// Diners: length 14, prefix 30, 36, or 38.
var re = /^3[0,6,8]\d{12}$/;
}
if (!re.test(ccnum)) return false;
// Remove all dashes for the checksum checks to eliminate negative numbers
ccnum = ccnum.split("-").join("");
// Checksum ("Mod 10")
// Add even digits in even length strings or odd digits in odd length strings.
var checksum = 0;
for (var i=(2-(ccnum.length % 2)); i<=ccnum.length; i+=2) {
checksum += parseInt(ccnum.charAt(i-1));
}
// Analyze odd digits in even length strings or even digits in odd length strings.
for (var i=(ccnum.length % 2) + 1; i<ccnum.length; i+=2) {
var digit = parseInt(ccnum.charAt(i-1)) * 2;
if (digit < 10) { checksum += digit; } else { checksum += (digit-9); }
}
if ((checksum % 10) == 0) return true; else return false;
}
//javascript/7108