为什么这个承诺返回未定义？

Question

I am trying to write a simple function like this

const joinLeague = async () => {
    const league = await attemptToJoinLeaugeIfItExists({ id, leaguePin })
    console.log(league, 'fl')

    if (league) {
        // do something 
    }
}

and I have made a firebase helper like this

export const attemptToJoinLeaugeIfItExists = ({ id, leaguePin }: any) => {
    return new Promise((res, rej) => {
        res(
            firebaseApp
                .database()
                .ref(`users/${id}`)
                .once('value')
                .then((snapshot) => { `
                    firebaseApp
                        .database()
                        .ref(`leagues`)
                        .once('value')
                        .then((snapshot) => {
                            console.log('in here')
                        })
                }),
        )
    })
}

however, league is logging out as undefined and in here is logging out second. however, I thought it would be the other way around? I thought it would "await" for this function to resolve then once it's resolved, it would show me the result. what am I doing wrong?

Answer 1

do it like this:

export const attemptToJoinLeaugeIfItExists = ({ id, leaguePin }: any) => {
    return firebaseApp
                .database()
                .ref(`users/${id}`)
                .once('value')
                .then((snapshot) => { `
                    return firebaseApp
                        .database()
                        .ref(`leagues`)
                        .once('value')
                })
}

you're currently immediately resolving your outer promise but with an inner promise, and that inner promise doesn't return anything at all, hence undefined. Just return the promise directly. Cleaner, simpler.