Why i can't use Primus.connect()? - node.js

Question

I download a example at https://github.com/strongloop/strong-pubsub-example
When I use Primus.connect(url). It's occurs error that: "Primus.connect is not a function".
This is my pub.js
var PORT = process.env.PORT;
var TOPIC = process.env.TOPIC;
var Client = require('strong-pubsub');
var Adapter = require('strong-pubsub-mqtt');
var readline = require('readline');
var client = new Client({port: PORT}, Adapter);
var rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
(function prompt() {
rl.question('to "' + TOPIC + '": ', function(answer) {
client.publish(TOPIC, answer);
prompt();
});
})();
And this is my sub.js
var PORT = process.env.PORT;
var TOPIC = process.env.TOPIC;
var Client = require('strong-pubsub');
var Adapter = require('strong-pubsub-mqtt');
var client = new Client({port: PORT}, Adapter);
client.subscribe(TOPIC);
var duplex = require('duplex');
var Primus = require('primus');
Primus.Stream = require('stream');
var server = new Client({port: PORT, host: 'localhost'}, Adapter, {
createConnection: function(port, host) {
var connection = duplex();
var primus = Primus.connect('http://' + host + ':' + port, {
transformer: 'engine.io',
parser: 'binary'
});
connection.on('_data', function(chunk) {
// someone called `connection.write(buf)`
primus.write(chunk);
});
primus.on('data', function(chunk) {
// chunk is an arrayBuffer
connection._data(toBuffer(chunk));
});
primus.on('open', function() {
connection.emit('connect');
});
connection.on('_end', function() {
primus.end();
this._end();
});
return connection;
}
});
client.on('message', function(topic, msg) {
console.log(msg.toString());
server.publish(topic,msg);
});
And errors