Ajax should not be mistaken to be a programming language or tool, but it is rather a concept of a client sided script that communicates to and from a server or database without the requirement for a post back or a complete page refresh. The meaning of Ajax is Asynchronous JavaScript and XML, where asynchronous means multiple events that are happening independently of one another. A proper definition for Ajax is that it is a method of exchanging data with a server, and updating part of the webpage without the need to reload the whole page.
There are various benefits of using the technique of Ajax as it helps to create fast and dynamic web pages. The four main benefits of using Ajax in web applications, those are call-backs, making asynchronous calls and, making the site user-friendly and increasing the speed. Ajax is used to make a callback which is a quick round trip to and from the server to save or retrieve data whereby the need to post the whole page back to the server is not required. Network utilisation is also maximised and faster operations occur by not performing a full postback and sending all form data to the server that is the server does not require to reload the whole page when making any updates on the backend. Users can continue to use the application while the client program request information from the server in the background.
Ajax is based on internet open standards and uses a combination of these such as XML Http Request object to exchange date asynchronously with a server, CSS (Cascading Style Sheets) to style the data, JavaScript/DOM to display and interact with the information, and data stored in XML format that are fetched from the server. JavaScript is a loosely typed scripting language that acts as the glue for the whole AJAX operation and its function is called when an event occurs in a page, whereas CSS allows for a clear separation of the presentation style from the content and may be changed programmatically by JavaScript. DOM (Document Object Model) is the API (Application Programming Interface) for accessing and manipulating structured documents, and it represents the structure of XML and HTML documents. There are various famous web applications which are using AJAX such as Google Maps, Google Suggest, Gmail and Yahoo Maps. For example when using Google Maps a user can simply drag the entire map by using the mouse instead of clicking on a button to reload the page to get other part of the map.
With the ever changing online technologies, many websites have not been able to keep up with these updates and there are just a bunch of websites that use the concept of Ajax.