Referencing firebase database with a variable and string concatenation

Question

As you can see below i'm trying to read a list of data from the database and then loop over the result, in javascript. The function runs whenever i open/refresh the page:

firebase.database().ref("Users/" + uid + "/rooms").on("value", function(snapshot) {

    snapshot.forEach(function(e) {

         var element = e.val();

         var roomId = element.Id;

    });
});

However, that string concatenation to specify the User Id doesn't work for some reason. When i replace it with the user Id directly like this:

firebase.database().ref("Users/GR3JFsMrKOjCrLhDNFMaq72COd07/rooms").on.....

that works fine. But of course i want to use the variable which contains the Id of the current user.

The uid variable is assigned a value in the onAuthStateChanged when checking if the user is signed in:

firebase.auth().onAuthStateChanged(function(user) {
if (user) {
// User is signed in.

uid = user.uid;

If I add a console.log like this:

firebase.database().ref("Users/" + uid + "/rooms").on("value", function(snapshot) {

console.log(snapshot.parent);

    snapshot.forEach(function(e) {

the output with the first code example (using uid variable) is: undefined. If i specify the User Id directly it is: room-id-1 (the result i want).

How do i make the string concatenation work? Or is this the wrong way of specifying the path of the current user?

Please update question to clarify when your code is being executed and how uid variable is initialized... Additionally, please concider using ‘let’ for declaring variables whenever suitable since scoping/hoisting can get verry messy with asyncs ;) — Mladen, May 19 '18 at 11:08

score 2 · Accepted Answer · answered May 19 '18 at 14:05

It is extremely unlikely that the problem is in the string concatenation itself. It is much more likely that uid simple doesn't have a value yet when you start reading from the database.

To make sure the uid is available, put the reading of the data into the auth state listener like this:

firebase.auth().onAuthStateChanged(function(user) {
  if (user) {
    uid = user.uid;
    console.log("uid="+uid);
    firebase.database().ref("Users/" + uid + "/rooms").on("value", function(snapshot) {
      snapshot.forEach(function(e) {
        var element = e.val();
        var roomId = element.Id;
        console.log("roodId="+roomId);
      });
    });
  }
})

Referencing firebase database with a variable and string concatenation

1 Answers1

Linked