How to pass a third argument to a callback using B

Question

With a little help I've arrived at the following code to promisify a passport.js login strategy.

var passport = require('passport');
var LocalStrategy = require('passport-local').Strategy;
var Promise = require('bluebird');
var bcrypt = require('bcrypt');
var db = require('./db').db; //users are stored in mongo

//I'm using bluebird.js for promises
var users = Promise.promisifyAll(db.users);
var compare = Promise.promisify(bcrypt.compare);


// This strategy is used by passport to handle logins
module.exports.localStrategy = new LocalStrategy(function(username, password, done) {
  users.findOneAsync({username: username}).bind({})
    .then(function(user) {
        if (!user) {
          throw new NoMatchedUserError('Incorrect username.');
          //should be equivalent to:
          // return done(null, false, {message:'something'});
        }
        this.user = user;
        return compare(password, user.password);
    })
    .then(function(isMatch) {
      if (isMatch) {
        return this.user;
        //is equivalent to:
        // return done(null, this.user);
      }
      else {
        throw { message: 'Incorrect password.' };
        //should be equivalent to:
        // return done(null, false, {message:'something else'};
      }
    })
    .nodeify(done);
});

by calling nodeify(done) I can handle the path where passwords match but I don't know how to pass the optional third parameter out so that passport.js can use it.

Is it possible to have the two failure (not error) paths handled?

---

Update:

As asked in the comments I created an issue on Github and this feature was (very promptly) added in Bluebird v2.0

https://github.com/petkaantonov/bluebird/issues/219

Answer 1

I'm adding this answer to show how to use .nodeify(done, {spread: true}) (as mentioned in other answers/comments) with the original example.

var passport = require('passport');
var LocalStrategy = require('passport-local').Strategy;
var Promise = require('bluebird');
var bcrypt = require('bcrypt');
var db = require('./db').db; //users are stored in mongo

//I'm using bluebird.js for promises
var users = Promise.promisifyAll(db.users);
var compare = Promise.promisify(bcrypt.compare);

// This strategy is used by passport to handle logins
module.exports.localStrategy = new LocalStrategy(function(username, password, done) {
  users.findOneAsync({username: username}).bind({})
    .then(function(user) {
        if (!user) {
          return [false, { message: 'Incorrect username.' }]; <---------------
          //should be equivalent to:
          // return done(null, false, {message:'something'});
        }
        this.user = user;
        return compare(password, user.password);
    })
    .then(function(isMatch) {
      if (isMatch) {
        return this.user;
        //is equivalent to:
        // return done(null, this.user);
      }
      else {
        return [false, { message: 'Incorrect password.' }]; <---------------
        //should be equivalent to:
        // return done(null, false, {message:'something else'};
      }
    })
    .nodeify(done, {spread: true});
});

Answer 2

Use:

.nodeify(done, {spread: true});

This allows multiple arguments to be passed to the 'done' callback.

More info on:

Bluebird nodeify documentation

Answer 3

Currently, there is no way to do it with .nodeify, you can of course do it manually with .then:

.then(function(result){
     done(/*whatever arguments you need*/);
},function(failure){
     done(/* failure argumnets */);
});