ibanvalidator.js

function validateIBAN(iban) {
    var newIban = iban.replace(/ /g, '').toUpperCase(),
        modulo = function (divident, divisor) {
            var cDivident = '';
            var cRest = '';

            for (var i in divident ) {
                var cChar = divident[i];
                var cOperator = cRest + '' + cDivident + '' + cChar;

                if ( cOperator < parseInt(divisor) ) {
                        cDivident += '' + cChar;
                } else {
                        cRest = cOperator % divisor;
                        if ( cRest == 0 ) {
                            cRest = '';
                        }
                        cDivident = '';
                }

            }
            cRest += '' + cDivident;
            if (cRest == '') {
                cRest = 0;
            }
            return cRest;
        };

    if (newIban.search(/^[A-Z]{2}/gi) < 0) {
        return false;
    }

    newIban = newIban.substring(4) + newIban.substring(0, 4);

    newIban = newIban.replace(/[A-Z]/g, function (match) {
        return match.charCodeAt(0) - 55;
    });

    return parseInt(modulo(newIban, 97), 10) === 1;
}