Confusing JavaScript object behaviour

Question

I’m using Socket.IO with Node.js.

I have an object socket which looks like this:

SocketNamespace
    $events: Object
    ...
    socket: Socket

So then If I look at Socket (i.e. socket.socket)

Socket
    $events: Object
    ...
    sessionid: "1549988601982716407"

Again, works fine.

But if I just want to return sessionid, so I use socket.socket.sessionid I get...

undefined

If I do a typeof for socket.socket I get object, but for socket.socket.sessionid, I just get undefined.

Edit: here’s my code:

Browser:

$(function() {

    $.getScript('http://localhost:8080/socket.io/socket.io.js', function() {
        var socket = io.connect('http://localhost:8080');
        console.log(socket.socket.sessionid);
    });

});

App:

var io = require('socket.io').listen(8080);

io.sockets.on('connection', function (socket) {

});

Edit 2: More data:

Instead of the one log, I’ve replace with this;

console.log(typeof(socket));
console.log(typeof(socket.socket));
console.log(typeof(socket.socket.sessionid));

Returns:

object
object
undefined

Expected:

object
object
string

Edit 3:* Screenshot

Edit 4

This, oddly, works.

var x;
for (x in socket.socket)
{
    if (x == 'sessionid') {
        console.log(socket.socket[x]);
    }
}

Please don't quote pseudo-code. Your problem is likely down to the actual code you use. We can't help you if you don't quote the actual code. — T.J. Crowder
– T.J. Crowder, Commented Jan 12, 2012 at 22:51
I’ve added the code – but it’s just standard stuff, didn’t see the need to fill up the page with code. — Zoe Edwards
– Zoe Edwards, Commented Jan 12, 2012 at 23:20
So in your original sample you reference sessionid, but in your edited code you cite session_id. Could this be the problem? Should it be sessionid? — Treffynnon
– Treffynnon, Commented Jan 12, 2012 at 23:21
Sorry no I’d accidentally typed it when typing the console.log back in for the test code. I’ve just tested it again and it’s still doing what it did before. — Zoe Edwards
– Zoe Edwards, Commented Jan 12, 2012 at 23:23
@ThomasEdwards: The code's no longer than the pseudo-code, and much more precise. — T.J. Crowder
– T.J. Crowder, Commented Jan 12, 2012 at 23:24

Felix Loether · Accepted Answer · 2012-01-12 23:53:04Z

1

socket.socket.sessionid is indeed valid and contains the session id once it's set. The problem is it's not set at the moment you print it to the console, since the socket hasn't made a connection yet (and thus doesn't have a session id).

Change the lines

var socket = io.connect('http://localhost:8080');
console.log(socket.socket.sessionid);

to

var socket = io.connect('http://localhost:8080');
socket.on('connect', function () {
    console.log(socket.socket.sessionid);
});

and everything should be golden.

answered Jan 12, 2012 at 23:53

Felix Loether

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1 Comment

Zoe Edwards Over a year ago

Sadly that hasn’t worked for me – still sends undefined. Thanks for your input, that does make sense.

Zoe Edwards · Accepted Answer · 2012-01-23 22:00:29Z

0

I can’t believe this.

socket.socket['sessionid']

That worked. Thanks all.

answered Jan 23, 2012 at 22:00

Zoe Edwards

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Comments

Nick Olszanski · Accepted Answer · 2014-05-24 20:25:10Z

I will try to explain WHY the error occured in the first place.

The TC, was looking at Chrome dev console and it was showing some data. But

console.log(typeof(socket));

and

console.log(typeof(socket.socket.sessionid));

do not produce equal output.

If you look at Chrome console, you will see a small "i" symbol near the object.

This means, that when you try to access sessionid it doesn't actually have it. Try e.g. with open property. You will see that it shows something different from the object output.

But when you click it in a console, it produces it on the fly.

If you need a working code, it looks like this:

// SERVER. Place it where you first _receive_ a connection from a client.
socket.emit('connected'); 
// This will emit connected message. 
//It is a signal to your client, that there is an established CLIENT<->SERVER connetion

// CLIENT
socket.on('connected', function (){
console.log(socket.socket.sessionid);} // This produces correct sessionid

Now, this will produce a valid sessionid on a client side.

As you see, in your example you simply try to access a not-yet existing property. A couple of milliseconds too fast ;)

I hope that is clear now.

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