Firebase onDisconnect not 100% reliable now?

Question

I've been using Firebase extensively and still face only one real issue: onDisconnect isn't 100% reliable in my experience.

If you close a computer without closing the window first, or kill the browser, you sometime have the "garbage collector" getting your onDisconnect executed, sometimes it doesn't.

My question is the following: I just don't use /.connected for now, I basically use a simple

userRef.set('status', 1);
userRef.onDisconnect().update({ 'status' : 0 });

Is there anything wrong with this approach? Do we agree that the update parameters are passed to the server at the time the line is executed and not before window unload ?

NB: I happen to try to keep a multi-window status, using the following approach to keep the status at 1 if another window is closed:

userRef.child('status').on('value', function(snap) {
  if (snap.val() != 1) {
    userRef.set('status', 1);
  }
});

I don't this how this could be related, but...

MY SOLUTION: In fact, I had just missed the part where you learn that onDisconnect is only triggered once. To get a persistent onDisconnect, you need to implement basic persistence.

Helpers.onConnected = function(callback) {
    var connectedRef = lm.newFirebase('.info/connected');
    var fn =  connectedRef.on('value', function(snap) {
      if (snap.val() === true) {
          if (callback) callback();
      }
    });
    var returned = {};
    returned.cancel = function() {
        connectedRef.off('value', fn);
    };
    return returned;
};       

Simple use case:

        this._onConnected = lm.helpers.onConnected(function() {
            this.firebase.onDisconnect().update({ 'tu': 0 });
        }.bind(this));

And then to cancel:

        if (this._onConnected) this._onConnected.cancel();
        this.firebase.onDisconnect().cancel();

Answer 1

Expanding on the comment :

This is why we provide the /.info/connected endpoint. 
We recommend re-establishing the disconnect handler every time the connection comes back online

I followed the above and got it fixed:

const userRef = Firebase.database().ref('/users/<user-id>')

Firebase.database()
  .ref('.info/connected')
  .on('value', async snap => {
    if (snap.val() === true) {
      await userRef.onDisconnect().remove();
      await userRef.update({ status : 'online' })
    } else {
      await this.userRef.remove()
    }
});

For reference, my previous code was:

const userRef = Firebase.database().ref('/users/<user-id>')
userRef.onDisconnect().remove();
await userRef.update({ status : 'online' })

The issue with this is that the onDisconnect may not work when you go offline and come back online multiple times