从 firebase 函数返回数据返回 null

Question

I have this code

exports.battle = functions.https.onCall((data, context) => {
    if(context.auth){
        var difficulty = randInt(2,10) / 10
        var user = context.auth["uid"]
        
        var userHP
        var userLevel
        var userDmg 
        var resultUserDmg = []
        var resultUserHp = []

        var monsterHP
        var monsterLevel
        var monsterDmg
        var resultMonsterDmg = []
        var resultMonsterHp = []

        

        var ref = db.ref(`players/${user}`);
        ref.child("hp").once("value", (snapshot) => {
           userHP = snapshot.val()
           monsterHP = userHP * difficulty

           ref.child("level").once("value", (snapshot) => {
                userLevel = snapshot.val()
                monsterLevel = userLevel * difficulty

                console.log("type"+typeof(userHP))
                console.log("value"+userHP)
                

                console.log("type"+typeof(monsterHP))
                console.log("value"+monsterHP)
                console.log("diff "+difficulty)


                while (userHP > 0 && monsterHP > 0){
                    userDmg = randInt(7, 14) * userLevel
                    monsterDmg = randInt(7, 14) * userLevel * difficulty


                    userHP = Math.round((userHP - monsterDmg)*10) /10;
                    console.log("userHP"+(userHP))
                    console.log("monsterDmg"+monsterDmg)
                    resultMonsterDmg.push(Math.round(monsterDmg*10) /10)
                    resultUserHp.push(Math.round(userHP*10)/10)
                    monsterHP = Math.round((monsterHP - userDmg)*10) /10;
                    console.log("userDmg"+userDmg)
                    console.log("monsterHP"+monsterHP)
                    resultUserDmg.push(Math.round(userDmg*10)/10)
                    resultMonsterHp.push(Math.round(monsterHP*10)/10)
                    console.log("----------")
                }

            
                var ref = db.ref(`players/${user}/coins`);
                ref.once("value", function(snapshot) {
                    var coinsNow = parseInt(snapshot.val());
                    const userRef = db.ref(`players/${user}`);
                    userRef.update({
                        'coins' : coinsNow+1
                    })
                });

                var result ={
                    userDmg : resultUserDmg,
                    userHp : resultUserHp,
                    monsterDmg : resultMonsterDmg,
                    monsterHp : resultMonsterHp,
                    monsterLvl : monsterLevel,
                };
                console.log("result is "+resultUserDmg)
                console.log("result is "+resultUserHp)
                console.log("result is "+resultMonsterDmg)
                console.log("result is "+resultMonsterHp)
                console.log("result is "+monsterLevel)
                return result 

            })
        })
    }
    else{
        console.log("User is not logged")
    }

    
})

Simply what this code does is that it calculates the player's life and damage against the monster using a while loop. This works correctly. The problem is when I want to send the data in the result variable to the user for further work. It returns null every time. Do you know where the error is? The only thing I can think of is that the error would be in the return. Maybe it gets called before the requested data has any value. I don't know. I can't figure it out.

But I am sure that the values I want to send to the user are not null but have the values they should have. Here is the log from the firebase console

Firebase console log

Here is code that i am useing for client returning. I always get null here

var battle = firebase.functions().httpsCallable('battle')
    battle().then(result => {
        console.log(result)
    })

UPDATE: Frank's response was great direction. But I don't think it's entirely clear. After a longer search, I found a more understandable solution for me here: https://medium.com/@stephane.giron/firebase-cloud-functions-oncall-returned-before-end-of-the-function-2d898d8ff259

I simply changed this at the beginning of the code ann add this to the end

exports.battle = functions.https.onCall((data, context) => {
    if(context.auth){
         return new Promise(function(resolve, reject) {
                
                 /* 
                   . . . .                       
                     code 
                   . . . .
                            */

                 reslove(result)
)}

I hope this has helped someone else. I recommend adding .catch to the end of the code for possible errores but I'm not entirely sure so I don't want to possibly confuse

Answer 1

Results from Promises bubble up to the caller, but only if you actually return them from within your then or catch callbacks. So inside every once callback you'll need to ensure that you return the value to the caller.

So first up, you're missing a top-level return statement in your top-level Cloud Function, which means that your return result never makes it to the caller.

So:

return ref.child("hp").once("value", (snapshot) => {
  ...
})

Next up, you'll need to do the same for ref.child("level").once("value", (snapshot) => { and other individual once calls.

Finally, if you have a loop where you perform an asynchronous operation (such as once or update ) for each item in the loop, you can use Promise.all to wait for all of these operations to complete before completing the operation and return a value to the caller.

I recommend reading up on Promises here in Using Promises on MDN, in the Firebase documentation on terminating functions: sync, async and promises and by watching Doug's excellent video series linked there.

---

Unrelated, but this code is much more complex than needed:

var ref = db.ref(`players/${user}/coins`);
ref.once("value", function(snapshot) {
    var coinsNow = parseInt(snapshot.val());
    const userRef = db.ref(`players/${user}`);
    userRef.update({
        'coins' : coinsNow+1
    })
});

The Firebase Realtime Database nowadays has a built-in increment operation , which means that you can simplify this to:

db.ref(`players/${user}/coins`).set(firebase.database.ServerValue.increment(1));