How to close a pubnub connection?

I'm using pubnub in a node.js project. I can initialize pubnub and publish a message like:

Node.js

var PUBNUB = require('pubnub');
var pubnub = PUBNUB.init({
  publish_key   : 'demo',
  subscribe_key : 'demo'
});

var CHANNEL = 'test1234';

pubnub.subscribe({
  channel: CHANNEL,
  message: function (message) {
    console.log('Received message:', message);

    // unsubscribe again
    pubnub.unsubscribe({channel: CHANNEL});

    // PROBLEM: The node.js process does not exit because pubnub is still 
    //          active. How to close the pubnub connection so it's completely 
    //          gone from memory?
  },
  connect: function () {
    // send a test message
    pubnub.publish({channel: CHANNEL, message: 'hello world!'});
  }
});

But how can I close this pubnub instance? So that it's gone from memory and event loop and does not keep the node.js process running.

I can't find anything in the API documentation, and tried pubnub.close(), pubnub.destroy(), and pubnub.disconnect() without success.