AJAX stands for Asynchronous JavaScript And XML.
AJAX is based on JavaScript and HTTP requests.
AJAX is not a new programming language, but a technique for creating better, faster, and more interactive web applications.
With AJAX, your JavaScript can communicate directly with the server, using the JavaScript XMLHttpRequest object. With this object, your JavaScript can trade data with a web server, without reloading the page.
AJAX uses asynchronous data transfer (HTTP requests) between the browser and the web server, allowing web pages to request small bits of information from the server instead of whole pages.
AJAX is a browser technology independent of web server software.
AJAX Uses HTTP Requests
In traditional JavaScript coding, if you want to get any information from a database or a file on the server, or send user information to a server, you will have to make an HTML form and GET or POST data to the server. The user will have to click the “Submit” button to send/get the information, wait for the server to respond, then a new page will load with the results.
Because the server returns a new page each time the user submits input, traditional web applications can run slowly and tend to be less user-friendly.
With AJAX, your JavaScript communicates directly with the server, through the JavaScript XMLHttpRequest object
With an HTTP request, a web page can make a request to, and get a response from a web server - without reloading the page. The user will stay on the same page, and he or she will not notice that scripts request pages, or send data to a server in the background.
The XMLHttpRequest Object
By using the XMLHttpRequest object, a web developer can update a page with data from the server after the page has loaded!
AJAX - Browser Support
The keystone of AJAX is the XMLHttpRequest object.
Different browsers use different methods to create the XMLHttpRequest object.
Internet Explorer uses an ActiveXObject, while other browsers uses the built-in JavaScript object called XMLHttpRequest.
Source: W3Schools
