socket.io nodejs channels

node_socketio_example.js

io.sockets.on('connection', function (socket) {
  socket.on('message', function(topic){
    // adds this socket to the particular topic
    socket.join(trend);
  });

  // sends a message to all connected clients of topic 'my-trend'  
  socket.broadcast.to('my-topic').emit('a new post');

  socket.on('disconnect', function(topic){
    // remove the client from the specified topic
    // future broadcasts will not be sent to the topic
    socket.leave(topic);
  });
});

// accessing the socket based on the channel/room name
var socket = io.sockets.in('topic');