node.js socket.oi问题

var http = require('http');
var fs = require('fs');

var server = http.createServer(function (req, res) {
fs.readFile('./index.html', function(error, data) {
res.writeHead(200, { 'Content-Type': 'text/html' });
res.end(data, 'utf-8');
});
}).listen(3000, "127.0.0.1");
console.log('Server running at http://127.0.0.1:3000/');

// var io = require('socket.io').listen(server);这里报错