socket.io.users error from example - node.js

Question

So I 100% copy pasted a code from the link below and I get the error below. I have installed all the dependencies required. I have used socket.io previously without problems, but never socket.io.users. The goal is to identify each PC as user.
var chatUsers = socketUsers.Users.of('/chat'); //
^
TypeError: Object #<Users> has no method 'of'
at Object.<anonymous> (/var/www/100moneta/components_not_larval/socket-user.js:16:35)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at startup (node.js:119:16)
at node.js:902:3
My code:
var express = require('express');
var app = express();
var server = require('http').createServer(app);
var socketUsers = require('socket.io.users');
socketUsers.Session(app);//IMPORTANT
var rootIo = require('socket.io')(server); //default '/' as namespace.
var chatIo = rootIo.of('/chat');
var rootUsers = socketUsers.Users; /* default '/' as namespace. Each namespace has IT's OWN users object list,
but the Id of a user of any other namespace may has the same value if request comes from the same client-machine-user.
This makes easy to keep a kind of synchronization between all users of all different namespaces. */
var chatUsers = socketUsers.Users.of('/chat'); //
rootIo.use(socketUsers.Middleware());//IMPORTANT but no errors if you want to skip it for a io.of(namespace) that you don't want the socket.io.users' support.
chatUsers.use(socketUsers.Middleware());
chatUsers.on('connected',function(user){
console.log(user.id + ' has connected to the CHAT');
user.set('username', 'username setted by server side'); /*at the store property you can store any type of properties
and objects you want to share between your user's sockets. */
user.socket.on('any event', function(data){ //user.socket is the current socket, to get all connected sockets from this user, use: user.sockets
});
chatIo.emit('set username',user.get('username')); //or user.store.username
});
rootUsers.on('connected',function(user){
console.log('User has connected with ID: '+ user.id);
});
rootUsers.on('connection',function(user){
console.log('Socket ID: '+user.socket.id+' is user with ID: '+user.id);
});
rootUsers.on('disconnected',function(user){
console.log('User with ID: '+user.id+'is gone away :(');
});
//You can still use the io.on events, but the execution is after connected and connection of the 'users' and 'chatUsers', no matter the order.
rootIo.on('connection',function(socket){
console.log('IO DEBUG: Socket '+ socket.id+ ' is ready \n');
});
Link with the code and tutorial: https://www.npmjs.com/package/socket.io.users