index.html

<script src="/socket.io/socket.io.js"></script>
<script>
  var socket = io.connect();
  
  socket.on('a', function(){
    //alert(1);
  });
  
  
  socket.on('b', function (data) {
    alert(1);
  });
</script>

output log

   info  - socket.io started
   debug - served static /socket.io.js
   debug - client authorized
   info  - handshake authorized 21680558507223987
   debug - setting request GET /socket.io/1/jsonp-polling/21680558507223987/?t=1310062023833&i=0
   debug - setting poll timeout
   debug - client authorized for 
   debug - clearing poll timeout
   debug - jsonppolling writing io.j[0]("1::");
   debug - set close timeout for client 21680558507223987
   debug - setting request GET /socket.io/1/jsonp-polling/21680558507223987/?t=1310062023839&i=0
   debug - setting poll timeout
   debug - clearing poll timeout
   debug - jsonppolling writing io.j[0]("�16�5:::{\"name\":\"a\"}�16�5:::{\"name\":\"b\"}");
   debug - set close timeout for client 21680558507223987
   debug - discarding transport
   debug - cleared close timeout for client 21680558507223987
   debug - setting request GET /socket.io/1/jsonp-polling/21680558507223987/?t=1310062023842&i=0
   debug - setting poll timeout
   debug - discarding transport
   debug - cleared close timeout for client 21680558507223987

server.js

var static = require('node-static');
var file = new(static.Server)('.');
var app = require('http').createServer(function (request, response) { request.addListener('end', function () { file.serve(request, response); }); });

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

io.configure(function () {
  io.set('transports', ['jsonp-polling']);
});


app.listen(80);


io.sockets.on('connection', function (socket) {
  socket.emit('a');
  socket.emit('b');
});