node js create server and connect

Question

Look at the following code :

var server = net.createServer(function(socket) {
    //Code block A


    socket.on('connect', function() {
        //Code block B
    })

    socket.on('data' , function (data){
           //Code C     

    });

});

Is there a chance code block A will be executed and code block B won't and vice versa? And if so, in what cases?

For counter example : Once code A has been executed Code C can run multiply time, without Code A ever running again.

Answer 1

This smells a bit like an interview-type question but...

1) Neither A or B will run because there's no server.listen to make it start listening.

2) If you call .listen then A will run (if the .listen was successful) but B will not run until a client connects to the server. On a connection, A will run, then B (assuming a successful connection).

Answer 2

Well, providing you call .listen(), I think you'll find that You get an order of:

(Client connects) // "connect" event fires
   |
   v 
  [A]--*-----.  // This is the Socket's "connect" event firing.
       |     |  // B and C are bound to their respective events.
       |     |
       |     |
      [B] <--.  // Binds handler to "connection" event, but 
       |        // connection event fires instantly
       |
      [C] <--.  // "data" event is fired
             |
(Client sends data)

Furthermore, A will never begin execution after B as the socket reference that B is bound to is located within the scope of closure A.

@Joe, I also think this sounds interview'y, but what the hey!

Answer 3

If code in block B is executed, then code in block A must have been executed.