AJAX or Asynchronous Javascript and XML, is a group of techniques used in web development which allows a web page to communicate with a server without reloading the page. Using AJAX, applications on the web can exchange data with the server without interfering with the existing web page. Although the “X” is intended to stand for XML, it is not necessary to use XML for the exchange of data. JSON can be used instead.
In computer programs, operations are ‘asynchronous’ if they operate independently of other processes. This is why the web page doesn’t have to be reloaded in order to send information to the server. The exact method for this uses something called an XMLHttpRequest object, which is effectively an interface that allows scripts to perform AJAX requests.
AJAX is not just one technology. All of these technologies work together to create a single HTTP or HTTPS request. According to Jesse James Garrett, who first coined the term, the following technologies are incorporated:
- HTML
- CSS
- Document Object Model
- XML
- XMLHttpRequest Object
- Javascript
In WordPress, AJAX can be seen in action in the post edit screen where you can add a new category while writing a post without reloading the page. Another example can be seen on the comments page where you can approve or delete a comment without reloading the page.