Can I create global variables in q promises in node?

Question

Before (trying) to switch to promises, I could have variables that were in the whole scope of the nested functions. For example, I could get a user from a database, not use it right away, then use it in a function nested far along in the chain.

So, with promises, must I explicitly pass the needed variables into the next function? Or is there some other way to get around this?

Currently my code looks something like this

exports.add = function ( req, res ) {
    var defer = q.defer()

    // check sign in and get user information as 'user' 

    function getUser ( req, res ) {
        User.findOne( { token: req.token }, function ( err, user ) {
            if ( err || !user )
                return res.json( {
                    status: "error",
                    message: "Error authenticating: " + err
                })

            return user
        })
    }

... // more functions here

defer.promise
.then( getUser )
.then( youtubeAuthenticate )
.then( getVideoId )
.then( youtubeFind )
.then( makeVideoObject )

defer.resolve( req, res )
}

The trouble is I can't access user in functions like makeVideoObject.

---

EDIT: Another thing that is really stumping me is how some of my functions can return a value, say videoId and that seems to be recognized by my final function, makeVideoObject, but others aren't, with no real difference between them. remain in scope, others become undefined.

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EDIT2: The reason my variable videoId was "global" was because I guess I was declaring it like videoId = .... So it wasn't the return videoId that made it global, but the way of declaring it. In that vain, I did this,

function getUserData () {
    user = getUser()
    videoId = getVideoId()
    youtubeAuthenticate()
}

function getVideoData () {
    vData = youtubeFind()
}   

defer.promise
.then( getUserData )
.then( getVideoData )
.then( function (user, videoId, vData ) {
    makeVideoObject( user, videoId, vData )
})

defer.resolve()

But no joy. Everything is still undefined.

---

EDIT3: I've tried the responses below and any permutations I can think of. Here is what I have at the moment.

var user = getUser()
var videoId = getVideoId()
var video = q(videoId).then( youtubeFind )

q.all( [ user, video ] ).then( function( results ) {
    if ( !results[0] )
        return res.json( "Not authenticated." )

    makeVideoObject( results[0], results[1] )
})

Using the debugger, both results are undefined. Using console.log within the getUser() and youtubeFind() functions, I see they work. Here is the getUser() function, for example.

function getUser () {
    User.findOne( { token: req.token }, function ( err, user ) {
        return user
    })
}

Also note I've simplified things by adding the authenticateYoutube() stuff right into youtubeFind().

---

Answer: I will probably choose an answer below out of courtesy, but this was a series of misunderstandings about Node and JS that made this problem. This doesn't answer the question as posed, but here's what I was doing wrong.

First, I thought that return, when put in a nested function (closure) should be the return <VALUE> for the "root" function it was nested in. Actually, it will only be the return value for the immediate function it's in. Probably JS 101 here. It also doesn't seem to be possible to affect variables declared in parent functions from within nested functions.

Second, you need to actually construct a function in a certain way for it to work like a promise. That format is like this:

function getUser () {
    var defer = Q.defer()   // create the promise object
    User.findOne( { token: req.token }, function ( err, user ) {
        defer.resolve( user )   // add the return value to the object
    })

    return defer.promise    // return the object, with promise and value
}

Answer 1

If you want to run several tasks that don't depend on each other and then run a task which needs those values, you can do something like this:

Q.all([getUserData(), getVideoData()]).spread(function(user, video) {
   // user and video are available
   makeVideoObject(user, video)
});

all takes a list of promises which can be fetched in parallel; spread splits those return values into individual params which can then be used inside the callback. Is that what you're trying to do?

Answer 2

As Benjamin Gruenbaum has said You're Missing the Point of Promises.

Promises are not simply a utility for stringing together callbacks. They are a placeholder for a future value.

So if you want to hold onto a result from somewhere midway through your list of steps, you just need to grab it:

var user = getUser();

user.then(doSomethingWithUser);
user.then(doSomethingElseWithUser);

You haven't shown us what your functions actually do, so I'll make my best guess to show you how you can gather the pieces you need and then recombine them. I'm not sure if by "q", you are referring to Q, or to $q, or to something else entirely, so I'll assume a minimum of convenience methods are available:

// All variables declared with "var" below are promises

var user = getUser();
var videoId = user.then(getVideoId); // assumes getVideoId depends on user
var youTubeAuth = user.then(youTubeAuthenticate);

var videoData = q.all([youTubeAuth, videoId]).then(function (values) {
    return getVideoData(values[0], values[1]);
});

var videoObject = q.all([user, videoId, videoData]).then(function (values) {
    return makeVideoObject(values[0], values[1], values[2]);
});