Validate Credit Card #JS

Asset.js

function isCreditCard( CC ){
    if (CC.length > 19)
        return (false);
 
    sum = 0; mul = 1; l = CC.length;
    for (i = 0; i < l; i++){
        digit = CC.substring(l-i-1,l-i);
        tproduct = parseInt(digit ,10)*mul;
        if (tproduct >= 10)
            sum += (tproduct % 10) + 1;
        else
            sum += tproduct;
        if (mul == 1)
            mul++;
        else
            mul–;
    }
    if ((sum % 10) == 0)
        return (true);
    else
        return (false);
}