request/response, websocket(flashsocket,ajax…).

var io = require('socket.io').listen(8080);
io.sockets.on('connection', function (socket) {
socket.emit('news', { hello: 'world' });
socket.on('my other event', function (data) {
console.log(data);
});
});

<script src="socket.io.min.js"></script>
<script>
  var socket = io.connect('http://localhost:8080');
  socket.on('news', function (data) {
    console.log(data); 
    socket.emit('my other event', { my: 'data' });
  });
</script>