These applications run on the client, that is, on the users browser while maintaining asynchronous communication with the server in the background. This way it is possible to make changes on the pages without having to recharge them, improving the interactivity, speed and usability in the applications.
Ajax is a combination of four existing technologies:
Like DHTML, LAMP or SPA, Ajax is not a technology in itself, but a term that encompasses a group of these working together.
Remote Scripting Frameworks such as ARSCIF appeared in 2003 shortly before Microsoft introduced Callbacks in ASP. NET.
Since XMLHttpRequest is implemented in most browsers, alternative techniques are rarely used. However, they are still used where greater compatibility, reduced implementation, or cross-site access is required. An alternative, the SVG Terminal (based on SVG), employs a persistent connection for the continuous exchange between the browser and the server.
Pages dynamically created by successive AJAX requests are not automatically registered in the browser history, so by clicking the "back" button of the browser, the user will not be returned to an earlier state of the page, instead you can go back to the last page you visited. Solutions include the use of invisible IFrames to trigger changes in the browser history and the change of the anchor portion of the address (after a #).
There are problems using Ajax between domain names, this is known as Same Origin Policy, which is a security measure, which can be solved with Cross-Origin Resource Sharing (CORS).
Depending on how the website is developed, you can improve or worsen the load on the server. Ajax can help the server avoid the html rendering phase, leaving that work to the client, but it can also overload the server if several calls are made to Ajax.
It is possible that pages with Ajax can not work on mobile phones, PDAs or other devices. Ajax is not compatible with all software for the blind or other disabilities.
Browsers that allow Ajax
It should be noted that this is a general list, and support for Ajax applications will depend on the features that the browser allows.
Gecko-based browsers such as Mozilla, Mozilla Firefox, SeaMonkey, Camino, K-Meleon, IceWeasel, Flock, Epiphany, Galeon and Netscape version 7.1 and above
WebKit-based browsers such as Google Chrome from Google or Apple Safari.
Microsoft Internet Explorer for Windows version 5.0 and above, and browsers based on it
Browsers with the KHTML API version 3.2 and above implemented, including Konqueror version 3.2 and above and the third generation Web Browser for S60 and later
Opera version 8.0 and above, including Opera Mobile Browser version 8.0 and higher.
Navigators that do not allow Ajax  source edit] Opera 7 and earlier
Microsoft Internet Explorer for Windows version 4.0 and earlier
Before Safari 1.2
Text-based browsers such as Lynx and Links
Browsers for people with special visual abilities (Braille)
Some mobile phone browsers