All the available browsers cannot support AJAX. Here is a list of major browsers that support AJAX.
When you write your next application, do consider the browsers that do not support AJAX.
Writing Browser Specific Code
It is for Opera 8.0+, Firefox, and Safari browsers. If it fails, we try two more times to make the correct object for an Internet Explorer browser with −
If it doesn't work, then we can use a very outdated browser that doesn't support XMLHttpRequest, which also means it doesn't support AJAX.
Most likely though, our variable ajaxRequest will now be set to whatever XMLHttpRequest standard the browser uses and we can start sending data to the server.