(JavaScript) Function returning an undefined value

Question

I have a function that reads from a Firebase database and would return any data it finds about a user.

authorize.js:

const login = (db, token) => {
    db.collection('users').get().then(async (e) => {
        var i = []
        e.forEach(async (doc) => {
            if (doc.data().access_token === token){
                i.push(doc.data().id)
                return doc.data()
            }
        })
        if (i.length === 0) return false
    }).catch((error) => {
        return false
    })
}
module.exports = login

app.js:

app.post('/token/:token', async (req, res) => {
    res.send(await login(db, req.params.token))
})

In authorize.js, I catch the error, but don't log it. When I console.log() the value that would've been returned directly inside the function, no errors occur and it gives me my desired result.

CherryDT · Accepted Answer · 2020-04-24 23:30:34Z

You are missing two returns. Also, you have the function inside the e.forEach async which means it will run after the rest of your code so you won't get your result, remove that (since you aren't doing anything async there anyway):

const login = (db, token) => {
    // v HERE v - you need to return the promise
    return db.collection('users').get().then(async (e) => {
        var i = []
        // v HERE v - no async
        e.forEach((doc) => {
            if (doc.data().access_token === token){
                i.push(doc.data().id)
                // Also, no need for a return here, since it doesn't do anything
            }
        })
        if (i.length === 0) return false
        return i // << instead, here was another return missing
    }).catch((error) => {
        return false
    })
}
module.exports = login

A clearer way would be to make login also async, then you could just use await there as well:

async function login (db, token) {
    try {
        const e = await db.collection('users').get()
        const i = []

        for (const doc of e) {
            if (doc.data().access_token === token){
                i.push(doc.data().id)
            }
        }

        if (i.length === 0) return false
        return i
    } catch (e) {
        return false
    }
}

module.exports = login

This could be further simplified:

async function login (db, token) {
    try {
        const matchingUserIds = await db.collection('users').get()
            .map(doc => doc.data())
            .filter(docData => docData.access_token === token)
            .map(docData => docData.id)

        return matchingUserIds.length ? matchingUserIds : false
    } catch (e) {
        return false
    }
}

module.exports = login

(I wonder though if there isn't any better method to filter the users by access token in your database. Right now it seems like you'll fetch all users and then check for the token in this function; it would probably be more scalable to query the database by token in the first place.)

Samson Ugwu · Accepted Answer · 2020-04-24 23:31:52Z

0

An async function always go with an await and am not seeing any await right inside the function.

More clarity.

answered Apr 24, 2020 at 23:31

Samson Ugwu

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1 Comment

CherryDT Over a year ago

This should be a comment, not an answer!

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