The scope of a JS array is being lost in Firebase

Question

The scope of a JS array is being lost in Firebase

The Firebase data structure looks like this:

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

Here is the code to retrieve election1 and election2:

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);
    }

Currently, the issue is that electionArr is empty. How can I resolve this problem?

javascript firebase firebase-realtime-database

Answer 1

Answer №1

It is important to remember that Firebase function calls operate asynchronously. This means that you cannot assign an array from a different scope inside the 'on' function call in Firebase. To ensure your array is accessible, it should be declared and manipulated within the 'once(value)' function.

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

Answer 2

It is important to remember that Firebase function calls operate asynchronously. This means that you cannot assign an array from a different scope inside the 'on' function call in Firebase. To ensure your array is accessible, it should be declared and manipulated within the 'once(value)' function.

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

Answer 3

Answer №2

The function known as once() operates asynchronously, as explained in detail in this insightful article. To ensure all the data is read before logging your array to the console, it's important to nest your reads:

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);
            });
        }
    });
}

Answer 4

The function known as once() operates asynchronously, as explained in detail in this insightful article. To ensure all the data is read before logging your array to the console, it's important to nest your reads:

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);
            });
        }
    });
}

The scope of a JS array is being lost in Firebase

Answer №1

Answer №2

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