server.js

var express = require('express'),
    app = express(),
    server = require('http').createServer(app),
    io = require('socket.io').listen(server),
    users = [];

app.use('/', express.static(__dirname + '/www'));
server.listen(process.env.PORT || 3000);
io.sockets.on('connection', function(socket) {

  socket.on('login', function (nickname) {
    if (users.indexOf(nickname) > -1 ) {
      socket.emit('nickExisted');
    } else {
      socket.userIndex = users.length;
      socket.nickname = nickname;
      users.push(nickname);
      socket.emit('loginSuccess');
      io.sockets.emit('system', nickname, users.length, 'login');
    }
  });

  socket.on('disconnect', function () {
    if (socket.nickname != null) {
      users.splice(socket.userIndex,1);
      socket.broadcast.emit('system', socket.nickname, users.length, 'logout');
    }
  });

  socket.on('postMsg', function (msg, color) {
    socket.broadcast.emit('newMsg', socket.nickname, msg, color);
  });

  socket.on('img', function (imgData, color) {
    socket.broadcast.emit('newImg', socket.nickname, imgData, color);
  });

});