IBAN Validation

validation.iban.js

// Modulo 97 for huge numbers given as digit strings.
function mod97(digit_string)
{
    var m = 0;
    for (var i = 0; i < digit_string.length; ++i)
        m = (m * 10 + parseInt(digit_string.charAt(i))) % 97;
    return m;
}

// Calculate 2-digit checksum of an IBAN.
/**
 * @return {number}
 */
function ChecksumIBAN(iban)
{
    var code     = iban.substring(0, 2);
    var checksum = iban.substring(2, 4);
    var bban     = iban.substring(4);

    // Assemble digit string
    var digits = "";
    for (var i = 0; i < bban.length; ++i)
    {
        var ch = bban.charAt(i).toUpperCase();
        if ("0" <= ch && ch <= "9")
            digits += ch;
        else
            digits += capital2digits(ch);
    }
    for (var i = 0; i < code.length; ++i)
    {
        var ch = code.charAt(i);
        digits += capital2digits(ch);
    }
    digits += checksum;

    // Calculate checksum
    return 98 - mod97(digits);

}

// Convert a capital letter into digits: A -> 10 ... Z -> 35 (ISO 13616).
function capital2digits(ch)
{
    var capitals = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    for (var i = 0; i < capitals.length; ++i)
        if (ch == capitals.charAt(i))
            break;
    return i + 10;
}