JavaScript algorithm

I’m unable to understand the algorithm mentioned here:
Can someone please help me out?

Can you be more specific about which part you have not understood?
I’ll briefly explain you what this file does. This file contains all the JavaScript functions to access the Bolt Cloud APIs to control the Bolt device.

The lines which have the keyword xmlhttp are used for doing AJAX calls to the API so that the page does not reload each time the function is called to fetch data or control the device.

Let me know if this answers your query.