SocketIO emit with callback fails while upgrading 0.9.16 to 1.3.5

Question

In 0.9.16, I use socket.emit with callback so that the chat server return some data and I can handle the result as per the acknowledgement. But after the upgrade to 1.3.5 I've found a error in console like this

Uncaught TypeError: Cannot read property 'apply' of undefined.

I've done something like this,

From web

socket.emit('userToUser', { 'usename': 'John',
'message': 'hi'
}, function(callback){
//callback handled
});

Chat Server

socket.on('userToUser', function(content, callback){
//do something
if(callback) return callback({'result':'success', 'messageid':content.messageid, 'chatid':content.chatid});
});

When I removed the callback from client side, there is no error. So I believe there will be some changes to be done in the callback.

I'm getting the acknowledgement and the chat is working properly, but my concern is about the console error which leads to socketio.js

Socket.prototype.onack = function(packet){
  debug('calling ack %s with %j', packet.id, packet.data);
  var fn = this.acks[packet.id];
  fn.apply(this, packet.data);
  delete this.acks[packet.id];
};

Guys, please help

Answer 1

Finally I've fixed the issue. It was a mistake in my code , I've done multiple callbacks in the chat server. like this:

socket.on('userToUser', function(content, callback){

  mysql.insertChat(content, function(err, data){
      return callback({'result':'1'})   //first callback
  })  
  sendToUser(content, function(errm successData){
      return callback({'result':'success','chatid':content.chatid});
      //second callback ->wrong
  })

});

In the previous versions it was a warning, now its an error !! That's it. So please avoid multiple callbacks

Please have a look at this and might be useful for every nodejs developer: http://www.toptal.com/nodejs/top-10-common-nodejs-developer-mistakes/#remote-developer-job

Thanks guys for upvoting !