I am new with NodeJs. why am I getting this error please Uncaught TypeError: Cannot read property 'prototype' of undefined ? I try to realise a chat with websockets. Help me please ! thanks

var html = require('fs').readFileSync(__dirname + '/simpleChat.html');
var server = require('http').createServer(function (req, res) {
  res.end(html);
});
server.listen(8080);
var nowjs = require('now');
var everyone = nowjs.initialize(server);
everyone.now.distributeMessage = function (message) {
  everyone.now.receiveMessage(this.now.name, message);
};