Are you running this from the Datamapper GUI? If so, the answer is here
If not, then try this:
var records = [].slice.call(data.records);
records.forEach(function(record) {
SequenceNumber = record.SequenceNumber;
CardNumber = record.HRN;
fileOut.write(SequenceNumber + ',' + CardNumber);
fileOut.newLine();
}
fileOut.Close();