Example express middleware flattened chain

update-user.js

var lookupUser, validateBody, mergeUser, saveUser, sendUserUpdatedEmail, returnSuccess;

lookupUser = function (req, res, next) { 
  User.findOne({
    _id: new ObjectId(req.params.id)
  }, function (err, user) {
    if (err) {
      res.status(500).send(err);
      return;
    }
    
    req.user = user;
    next();
  });
};

validateBody = function (req, res, next) {
  validator.run(rules, req.body, function (errorCount, errors) {
    if (errorCount) {
      res.status(400).send(errors);
      return;
    }
    next();
  }); 
};

mergeUser = function (req, res, next) {
  req.user = merge(req.user, req.body);
  next();
};

saveUser = function (req, res, next) {
  req.user.save(function (err, savedUser) {
    if (err) {
      res.status(400).send(errors);
      return;
    }
    req.user = savedUser;
  });
};

sendUserUpdatedEmail = function (req, res, next) {
  EmailClient.sendEmail(req.user.email, 'Your account was updated', function (err) {
    if (err) {
      res.status(500).send(err);
      return;
    }
    next();
  });
};

returnSuccess = function (req, res) {
  res.status(200).send(req.user);
};