What is AJAX and XHR ?

 XHR = XMLHttpRequest


The XMLHttpRequest is an object of navigation accessible with javascript which offers fetching datas woth JSON or XML format, and also HTML or simple text using an HTTP request

The XMLHttpRequest object is the key to AJAX. It can be used by JavaScript, JScript, VBScript, and many other web browser scripting languages to transfer and manipulate XML or JSON data to and from a webserver using Hyper Text Transfer Protocol(HTTP), establishing an independent connection channel between a webpage's Client-Side and Server-Side.

The data returned from XMLHttpRequest calls will be used by back-end databases. Besides XML, XMLHttpRequest can be used to fetch datas in other formats, like JSON or plain text.(*.txt)