after forEach the function returned an empty array

Question

I'm new in fullstack developing and I'm trying to do a function, in a REST API firebase project, that could filter my collection post by a friend list (gived as a sting with usernames separated by comma, ex:"user1,user2,user3"). After resolve, it gaves me an empty array but I've checked that all the data are correct. What can I do?

exports.getAllPosts = (req, res)=>{                                           //namespace delle funzioni,area https, onRequest  prende una richiesta ed una rispsota
var posts = [];                                         //array per i post

db
.doc(`/users/${req.user.handle}`).get()
.then(doc =>{
    var friends = doc.data().friends.split(',')
    friends.forEach(item=>{
        db
        .collection('posts')
        .where('userHandle','==', `${item}`)
        .orderBy('createdAt','desc')
        .get()                                                      //carica tutta la collezione posts
        .then(data =>{
            data.forEach(doc=>{                                     // ciclo per popolare l'array
                posts.push({
                    postId: doc.id,
                    body: doc.data().body,
                    game:doc.data().game,
                    userHandle: doc.data().userHandle,
                    createdAt: doc.data().createdAt,
                    ggCount: doc.data().ggCount,
                    commentCount: doc.data.commentCount,
                    userImage: doc.data().userImage
                });
            });  
        })
    })        
    return res.json(posts);
    
})
.catch(err => console.error(err));

}

domenikk · Accepted Answer · 2020-12-11T21:56:21.853

You're returning the posts array without waiting for it to be populated first. The db operations you're making are asynchronous, meaning when they complete the respective .then() block is executed; but the code below is executed right away.

I would rewrite it like this:

exports.getAllPosts = (req, res)=>{                                           //namespace delle funzioni,area https, onRequest  prende una richiesta ed una rispsota
    var posts = [];                                         //array per i post
    
    db
    .doc(`/users/${req.user.handle}`).get()
    .then(async doc => {
        var friends = doc.data().friends.split(',');
        for(const friend of friends) {
            const data = await db
                            .collection('posts')
                            .where('userHandle','==', `${friend}`)
                            .orderBy('createdAt','desc')
                            .get();

            data.forEach(doc => {                                     // ciclo per popolare l'array
                posts.push({
                    postId: doc.id,
                    body: doc.data().body,
                    game:doc.data().game,
                    userHandle: doc.data().userHandle,
                    createdAt: doc.data().createdAt,
                    ggCount: doc.data().ggCount,
                    commentCount: doc.data.commentCount,
                    userImage: doc.data().userImage
                });
            });
        }       
        return res.json(posts);
        
    })
    .catch(err => console.error(err));

after forEach the function returned an empty array

1 Answers1

I would rewrite it like this: