Firebase JS Array losing scope

Question

Firebase data is as follows

-users
--demo1
---conid:1
-election
--election1
---conRegex:1
--election2
---conRegex:1

the code to retrieve election1, election2 is

var conid;
    var conRegex;
    var electionArr = [];
    if(uidAnonymous != null) {
        db.ref('users/'+user).once('value', function(snapshot) {
            if(snapshot.exists()) {
                conid = snapshot.val().conid;
            }
        });
        db.ref('election/').once('value', function(snapshot) {
            snapshot.forEach(function(electionSnapshot) {
                conRegex = electionSnapshot.val().conRegex;
                if(conid.startsWith(conRegex)) {
                    electionArr.push(electionSnapshot.key.toString());
                }
            });
        });
        console.log(electionArr);
    }

Problem is electionArr is empty? How do i solve the issue

Himanshu · Accepted Answer · 2018-02-18 17:44:03Z

2

Firebase function calls are asynchronous. Thats how it works you cannot assign an array from out of scope inside firebase on function call. Make your array available inside your once(value) function.

var conid;
var conRegex;
if(uidAnonymous != null) {
    db.ref('users/'+user).once('value', function(snapshot) {
        if(snapshot.exists()) {
            conid = snapshot.val().conid;
        }
    });
    db.ref('election/').once('value', function(snapshot) {
        var electionArr = [];
        snapshot.forEach(function(electionSnapshot) {
            conRegex = electionSnapshot.val().conRegex;
            if(conid.startsWith(conRegex)) {
                Object.keys(electionSnapshot.val()).map(k => {
                    electionArr.push(electionSnapshot.val()[k]);
                })
            }
        });
        console.log(electionArr);
    });
}

edited Feb 18, 2018 at 17:44

answered Feb 18, 2018 at 10:07

Himanshu

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6 Comments

Mayank Metha Over a year ago

i need electionArr outside the if(uidAnonymous != null) then how will i do that?

Himanshu Over a year ago

I have edited the code. You needs to map through keys of returned snapshot object and push values to array

Himanshu Over a year ago

I have edited the code tell me If data is coming in electionArr now or not then we try further. Because I am unable to check the output

Mayank Metha Over a year ago

Not getting the expected results that is the electionSnapshot.key

Himanshu Over a year ago

what do you mean by expected output. Are you even getting values in electionSnapshot.val().

|

Rosário P. Fernandes · Accepted Answer · 2018-02-18 17:43:22Z

The once() function is asynchronous. You'll have to nest your reads and log your array to the console when all the data is read:

var conid;
var conRegex;
var electionArr = [];
if(uidAnonymous != null) {
    db.ref('users/'+user).once('value', function(snapshot) {
        if(snapshot.exists()) {
            conid = snapshot.val().conid;

            db.ref('election/').once('value', function(snapshot) {
                snapshot.forEach(function(electionSnapshot) {
                    conRegex = electionSnapshot.val().conRegex;
                    if(conid.startsWith(conRegex)) {
                        electionArr.push(electionSnapshot.key.toString());
                    }
                });
                console.log(electionArr);
            });
        }
    });
}

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