Retrieve data from Firebase database in JavaScript

Question

I am new to Firebase, and I am trying to figure out how to retrieve data from my Firebase database. I was able to add to it successfully based on a user's unique id (uid), but now getting data from it seems to be incredibly difficult. I want to grab the first name from the current user ('user' in the following code), but this JavaScript doesn't seem to be working:

var uid = user.uid
firebase.database().ref('users/' + uid).on('value', function(snapshot) {
    this.first_name = snapshot.val().first_name;
});

As soon as I make the call to this.first_name, it gives me the following error:

FIREBASE WARNING: Exception was thrown by user callback. TypeError: Cannot set property 'first_name' of null.

In case it helps, my database is structured like this:

{
  users: {
    "uid1": {
      first_name: "John"
    },
    "uid2": {
      first_name: "Sue"
    }
  }
}

Your assigning a value to this.first_name. What are you expecting this to be? Since you're in the middle of a callback chain, the this context may be a variety of things (including null). — John Green
– John Green, Commented Jun 9, 2016 at 6:02

MasterMohsin · Accepted Answer · 2016-06-09 06:19:47Z

3

Use var first_name instead of this.first_name. It should work.

var uid = user.uid
firebase.database().ref('users/' + uid).on('value', function(snapshot) {
    var first_name = snapshot.val().first_name;
});

answered Jun 9, 2016 at 6:19

MasterMohsin

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2 Comments

Anderillo Over a year ago

Thank you so much, that worked! However, I was using this.first_name before because I want to display that information in my HTML. Is there a way that I can do this?

Anderillo Over a year ago

OK, I figured it out. I just set the innerHTML to first_name.

Ami Hollander · Accepted Answer · 2018-02-20 09:53:51Z

3

The answer above is correct. but, i guess it's more readable if you use child in the query. Both should work.

firebase.database().ref('users').child(uid).on('value', function(snapshot) {
    var first_name = snapshot.val().first_name;
});

edited Feb 20, 2018 at 9:53

answered Jun 20, 2016 at 17:06

Ami Hollander

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