I know this must be a really silly question, but I can't figure out how to make it work. I'm learning node.js and mongojs, and this is my problem:

This is my server.js

server.get("/", function(request, response) {
  if (user.whatever()) {
    return response.send('true');
  } else {
    return response.send('false');
  }
});

and this my user.js

exports.whatever = function(request, response) {
  return db.tableName.findOne({
    fieldName: null
  }, function(error, record) {
    if (record === null) {
      return false;
    } else {
      return true;
    }
  });
};

the function returns "undefined". I imagine that this is a problem of blocking code, but have no idea on how to convert it. Please help!

You should do that as following :

server.js

server.get("/",user.whatever, function(request, response) {
  if (request.user)
    response.send('true');
  else
    response.send('false');
});

user.js

exports.whatever = function(request, response, next) {
  db.tableName.findOne({ fieldName: null }, function(error, record) {
    if (record === null) request.user = false;
    else request.user = true;
    next();
  });
};