generate control char of italian fiscal code

function getControlChar(surname, name, birth, gender, town) {
    if(surname == "")
        return "";
    if(name == "")
        return "";
    if(birth == "")
        return "";
    if(gender == "")
        return "";
    if(town == "")
        return "";
    birth = birth.substring(2);
    var vowels = "AEIOU";
    var consonants = "BCDFGHJLMNPQRSTVWXYZ";
    var surname_out = "";
    var name_out = "";
    var town_out = "";
    var i = 0;
    var j = 0;
    var c = 0;
    var ch = "";
    var temp = "";
    for (i = 0; i < surname.length; i++) {
        ch = surname.substring(i, i+1);
        for (j = 0; j < vowels.length; j++) {
            temp = vowels.substring(