AJAX, or Asynchronous JavaScript and XML, is an integrated method of web development that takes advantage of client-side technology of an individual’s computer system allowing the web developer to create interactive websites. What does it mean to be Asynchronous? Asynchronous communication is where the data can start to be processed before all information is completely received. This helps prevent idle processors.   With AJAX, a web site does not have to reload the whole page when retrieving new information, updating content, or opening a new page. Instead, the scripting allows for just the updated content to change while the elements that are unchanged on the page stay and are not reloaded or processed. This cuts down on download time of more complex sites and the processing required to handle the graphical load. Basically, AJAX technology has not come to refer to a large range of web applications that allows the client to communicate with the server in the background while not changing the current page of a website. Jesse James Garret tells us that AJAX technology is an incorporation of HTML (or XHTML with CSS to handle style), Document Object Model (DOM) for interaction with data and dynamic display, XML for the exchange of data (XSLT for its manipulation), XMLHttpRequest object (also known as ActiveX by some browsers) for the asynchronous communication of the data and JavaScript coding to bring all of these technologies together to work properly (w3schools).
In essence AJAX is a group of various technologies controlled usually by JavaScript coding, to allow the asynchronous communication of the client and server. AJAX is a server side technology while JavaScript is client side programming language. AJAX uses the concept of sending XMLHttpRequest. Depending on the browser the coding used to send request to the server can vary.
Here is a sample of coding that might be used to enable a pop up of a product on a store’s website.   The JavaScript coding is...