NodeJS Bluebird promise created in a handler but was not returned from it

Question

I have the following nodejs code as an express middleware function

Middleware.is_authenticated = function(req, res, next)
{
    if(req.system_session == unde         


        

Answer 1

This comes from the mix of promise-based code (Session.validate_session) with callback-based code (next). It would be expected that the next() call either is not asynchronous (doesn't create any promises) or returns that promise, which it doesn't (blame express).

There are two ways to avoid the warning:

• Let express do the error handling, and call next with an error if one occurs. In this case, you can use the .asCallback method:

  Middleware.is_authenticated = function(req, res, next) {
      if (req.system_session == undefined || req.system_session.login_status == false)
          var promise = Promise.reject(new Error('invalid_session'));
      else
          var promise = Session.validate_session(req.system_session, req.ip, req.headers['user-agent']);
  
      promise.asCallback(next);
  };
  

• As the warning explanation says, you can explicitly return null instead of returning the undefined value that next() yields:

  Middleware.is_authenticated = function(req, res, next) {
      if (req.system_session == undefined || req.system_session.login_status == false)
          var promise = Promise.reject(new Error('invalid_session'));
      else
          var promise = Session.validate_session(req.system_session, req.ip, req.headers['user-agent'])
          .catch(function(err) {
              req.system_session.destroy();
              throw err;
          });
  
      promise.then(function(session) {
          next();
          return null;
      }, function(err) {
          res.status(401).send({errors: true, error: err.message, session: req.system_session}).end();
      });
  };