Mod 10 (declarative fashion)

gistfile1.js

function mod10(numbers) {
    var multipliers = [2, 1];
    var multiplicands = numbers.reverse();
    var products = mapProducts(multiplicands, multipliers);
    var mod = products.map(
        function (number) {
            return number.toString().split('').map(
                function (str) {
                    return parseInt(str);
                }).sum();
        }).sum() % 10;
    if (mod >= 10) return 0;
    return 10 - mod;
}

Eu escrevi ontem

https://gist.github.com/2003306