Luhn check for cards

luhn.js

/*
* Validate the given card using the Luhn checksum algorithm. Returns `true` if the card 
* is valid, else returns `false`. 
* Example: 
* isCardValid("4242424242424242") // returns true
* isCardValid("4242424242424243") // returns false
*/
var isCardValid = (function (arr) {
    return function (ccNum) {
        var 
            len = ccNum.length,
            bit = 1,
            sum = 0,
            val;

        while (len) {
            val = parseInt(ccNum.charAt(--len), 10);
            sum += (bit ^= 1) ? arr[val] : val;
        }

        return sum && sum % 10 === 0;
    };
}([0, 2, 4, 6, 8, 1, 3, 5, 7, 9]));