Weryfikacja numeru IBAN rachunku

function isValidIBANNumber(input) {
    var CODE_LENGTHS = {
        PL: 28
    };
	
    var iban = String(input).toUpperCase().replace(/[^A-Z0-9]/g, ''),
            code = iban.match(/^([A-Z]{2})(\d{2})([A-Z\d]+)$/),
            digits;
			
    if (!code || iban.length !== CODE_LENGTHS[code[1]] ) {
        return false;
    }
	
    digits = (code[3] + code[1] + code[2]).replace(/[A-Z]/g, function (letter) {
        return letter.charCodeAt(0) - 55;
    });
	
    return mod97(digits);
}

function mod97(string) {
    var checksum = string.slice(0, 2), fragment;
    for (var offset = 2; offset < string.length; offset += 7) {
        fragment = String(checksum) + string.substring(offset, offset + 7);
        checksum = parseInt(fragment, 10) % 97;
    }
    return checksum;
}