Conventional web application transmit information to and

from the sever using synchronous requests. This means you

fill out a form, hit submit, and get directed to a new page

with new information from the server.

When you interact with an Ajax-powered web page, it loads an

Ajax engine in the background. In response to an event web

application passes asynchronous request (XMLHttpRequest or

xhr). In fact it is javaScript object/method that performs

asynchronous interaction with the server, JavaScript object

that performs asynchronous interaction with the server and

behind the scene fetches data. and behind the scene fetches

data.

We do request.xhr? only to check the request type, either

its AJAX request or others(post, get).