Returning a variable declared inside a Mongoose find()

Question

I'm having lots of trouble combining a for loop with promises. In essence, my workflow is:

1. Take an array of Artist objects in Node.js, and grab their biographies and IDs using Mongoose.
2. Use their IDs to get all the artwork (more specifically, all the artwork keywords) created by that artist.
3. Train them in a natural language processor classifier (this part isn't super relevant- just know that I need to have access to biography and keywords within the same outer scope.

However, I can't seem to use the bioText object inside the Mongoose promise, and I can't seem to return the keywords from the Mongoose promise.

            if (!isBlank(bioText) && bioText){
                bioText = artist.BIO;
                artworkIdArray.forEach((id)=> {
                        console.log(bioText) // <- prints correct values
                        var getKey = function(){
                    var words = Artwork.findById(id).then((artwork)=>{
                        console.log(bioText) // <- empty string
                    if(artwork.artworkKeywords.length > 0){
                        keywords = artwork.artistKeywords;
                        return keywords;
                    }
                }
                )
                return words;    
                }
                t=getKey();
                t.then((t)=>{
                    console.log(t); // <--- always undefined
                })
            }, this);
        }

As you can see, I try to console.log() after exiting the promise, but the t object is always undefined.

Additionally,

I know that in my example bioText is available right up until the Mongoose find() promise. But I also don't know how to inject bioText into the promise (because then I could simply just train the classifier inside the then() statement.

So my post is basically two questions:

1. Can Promises use outside variables inside then()?
2. How do I return a variable declared inside then() so it is available in the outer scope?

Answer 1

1. Can Promises use outside variables inside then()?

Yes, but you have to be careful with what happens to those variables later on. That's why console.log(bioText) may log a value just before DB call, and then log null just after DB response.

I would suggest you try the immediate invokation pattern to ensure the value is the expected one:

(function(x){...; console.log(x);})(bioText)

2. How do I return a variable declared inside then() so it is available in the outer scope?

You cannot, at least without complicated promise management, which you may not need here. That's why t=getKey(); is always undefined.

I think you want to get all the values before going on with your process. So you should retrieve all from DB in a single query, then call all your code in the callback.

You can have a try with this:

Artwork
    .find({_id: {$in: artworkIdArray}})
    .then( (artworks) => {
        var keywords = [];
        artworks.forEach( (artwork) => {
            if(artwork.artworkKeywords.length > 0)
                keywords.append(artwork.artistKeywords);
        });
        // Now do your job with all the retrieved keywords
    });