Short: belgian rijksregisternummer validation in javascript

It's been really busy, so no time for blog posts. In the meantime, here is a short function to validate id card numbers (rijksregisternummer) in Belgium, according to the official guidelines. I could not find a proper implementation of this in javascript.

        function IsRRNoValid(n) {
            // RR numbers need to be 11 chars long
            if (n.length != 11)
                return false;

            var checkDigit = n.substr(n.length - 2, 2);
            var modFunction = function(nr) { return 97 - (nr % 97); };
            var nrToCheck = parseInt(n.substr(0, 9));
            
            // first check without 2
            if (modFunction(nrToCheck) == checkDigit)
                return true;

            // then check with 2 appended for y2k+ births
            nrToCheck = parseInt('2' + n.substr(0, 9));

            return (modFunction(nrToCheck) == checkDigit);
        }

Easy as pie. You can get the gender and date of birth out of there as well, but I don't need that info for my purpose. A slightly more advanced validation would also check to see if the first 6 digits represent a valid date according to the yyMMdd format (determining the right century using the current validation).