Why can't I access properties in a nested JS Object? (Firebase Snapshot)

Question

TLDR: please scroll to part after JSON-snippet ;)

I'm currently working on a Firebase-Project. I'm writing code in JavaScript. Since hours I try to extract data from / write into an object, but for some reason I can't access it's params.

Initially my code looked as follows:

exports.updateUsersNewInterest = functions.database.ref('/category/{categoryID}/interest/{interestID}').onCreate(event =>{
        const interestID = event.params.interestID;
        const categoryID = event.params.categoryID;

        var ref = admin.database().ref("/userInterests/");
        ref.once("value").then(function(snapshot){
            snapshot.forEach(function(childSnapshot){

                var userID = childSnapshot.key;
                childSnapshotVal = childSnapshot.val();
                var rawSum = childSnapshotVal.rawSum;
                var rawCount = childSnapshotVal.rawCount;
                var norm = childSnapshotVal.norm;
                rawSum[interestID] = 0;
                rawCount[interestID] = 0;
                var resultObject = {};
                resultObject.norm = norm;
                resultObject.rawCount = rawCount;
                resultObject.rawSum = rawSum;               
                var ref1 = admin.database().ref("userInterests/"+userID);
                return ref1.set(resultObject);
            })
            return true
        })
        return true
})

Since for some reason I wasn't able to read the keys out of the single childSnapshot objects in the forEach, I had to use another attempt:

exports.updateUsersNewInterest = functions.database.ref('/category/{categoryID}/interest/{interestID}').onCreate(event =>{
        const interestID = event.params.interestID;
        const categoryID = event.params.categoryID;

        //console.log(categoryID);
        //console.log(interestID);

        var ref = admin.database().ref("/userInterests/");
        ref.once("value").then(function(snapshot){
            var data = snapshot.val();

            var keys = Object.keys(data);
            console.log(typeof snapshot);
            for (var i = 0; i < keys.length; i++){
//At this point I cant access any properties
//console.log(data[i][rawSum] for example is NOT working
            //  data[i][rawSum][interestID] = 0;
            //  data[i][rawCount][interestID] = 0;
            }
                var ref1 = admin.database().ref("userInterests/");
                return ref1.set(data);
        })
        return true
})

Now the thing is, when I try to console.log the key inside the for-loop, I get the right results. But performing any kind of action related to the properties of either $data or $snapshot (even though var data = snapshot.val() should give me an object?! is not working.

I might have lost some brackets copying the code from sublime to here but the general problem stays the same, even if my code-snippet is not complete here.

The firebase console gives me the error:

TypeError: Cannot read property 'rawSum' of undefined at

The object looks as follows:

{ '2wewe': 
   { rawCount: 
  { '11': 1,
    '17': 0,
    '18': 0,
    '19': 0,
    '33': 0,
    '35': 0,
    '36': 0,
    '40': 0 },
 rawSum: 
  { '11': 1,
    '17': 0,
    '18': 0,
    '19': 0,
...

So if I export a snapshot from Firebase and then extract its values via

var values = snapshot.val()

I should be able to e.g. writh into it with

var abc = values[id]['rawCount'][itemID]

or what am I missing?

And why is

snapshot.forEach(function(childSnapshot){
            var userID = childSnapshot.key;

just giving me "undefined"?

Would really appreciate any clue for my (probable rookie) problem.

Thanks in advance!

data[i][rawSum] != data[i]["rawSum"] (or data[i].rawSum) — James
– James, Commented Jan 12, 2018 at 19:36

Barmar · Accepted Answer · 2018-01-15 16:53:23Z

1

data[i] should be data[keys[i]]. But you can simply loop over the object keys directly, instead of calling Object.keys():

for (key in data) {
    if (data.hasOwnProperty(key)) {
        console.log(data[key].rawSum[interestID]);
        console.log(data[key].rawCount[interestID]);
    }
}

edited Jan 15, 2018 at 16:53

answered Jan 12, 2018 at 20:20

Barmar

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3 Comments

nnige Over a year ago

I tried it the way you suggested and it works! Thank you sir. Since I want to write to "data" and later rewrite the whole object into the database, I left out the if statement. There is no data-set for the given interestID unless I add one in the for-loop now. So as I understand it, I first go into the first node that has the key [key] and then look one level deeper for the node with the key [interestID]? Thanks again for your help.

Barmar Over a year ago

The purpose of the if statement is to skip properties that are inherited from the object's prototype. See blog.javascripting.com/2014/09/19/…

nnige Over a year ago

Ok, I migh have been off the track a bit. It's the first time I'm working with a prototype-based language. Thanks for the clarification, it makes absolutely sense!

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