socket.io.js引入报500错误

Question

环境是：
node 0.12.9
npm 3.8.6
express 4
socket.io1.4.5

index.html引入了/socket.io/socket.io.js之后，报500错误

app.js如下：

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');

// var routes = require('./routes/index');
// var users = require('./routes/users');

var app = express();
var server = require('http').createServer(app);
var io = require('socket.io')(server);

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

// uncomment after placing your favicon in /public
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

// app.use('/', routes);
// app.use('/users', users);
var users = {}; //存储在线用户对象
app.get('/',function(req,res){
    if(req.cookies.user == null){
        res.redirect('/signin');
    } else {
        res.render('index');
    }
});
app.get('/signin',function(req,res){
    res.render('signin');
});
app.post('/signin',function(req,res){
    if(users[req.body.name]){
        res.redirect('/signin');
    } else {
        res.cookie("user",req.body.name, {maxAge: 1000*60*60*24*30});
        res.redirect('/');
    }
});

io.sockets.on('connection',function(socket){
    console.log(2);
    socket.on('online',function(data){
        socket.name = data.user;
        //users对象中不存在该用户名则插入
        if (users[data.user]) {
            users[data.user] = data.user;
        }
        io.sockets.emit('online', {users:users, user:data.user});
    });
});
// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
  app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
      message: err.message,
      error: err
    });
  });
}

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
  res.status(err.status || 500);
  res.render('error', {
    message: err.message,
    error: {}
  });
});


module.exports = app;

启动用的是./bin/www
server.listen也在www里