Doing some socket.io work. Seems like my emit Callback is not being fired. Am I doing it right?

this.logger.debug("joining room " + roomId);      
callback = function() {
  return this.logger.debug('finished emitting join for socket');
};
// this.config.ioTypes.join resolves to "j"
this.socket.emit(this.config.ioTypes.join, { 
  user: this.config.user,
  room: roomId
}, callback);

My logging looks correct (note that the code above doesn't include everything that would generate these logs):

DEBUG: joining room 1245 

And that's the end. It looks like socket.io is not calling my callback. But the docs are pretty clear:

Sometimes, you might want to get a callback when the client confirmed the message reception.

To do this, simply pass a function as the last parameter of .send or .emit. What's more, when you use .emit, the acknowledgement is done by you, which means you can also pass data along:

Am I doing something wrong here?

Figured it out on my own. Gonna leave this here because the docs aren't very clear on this one.

I used util.inspect(arguments) to see what was coming in to my on handler on the server side (coffeescript):

  @logger.debug "onJoin args: " + util.inspect(arguments)

Which resulted in: ... '2': [Function: ack] which looked like what I needed. So I added that to the signature of the on handler. Then I added callback() if callback? to the end of the handler. Looks good so far.