If JavaScript is not activated, Ajax can't works. The user must be asked to set JavaScript from within options of the browser, with the "noscript" tag.
- Since data to display are loaded dynamically, they are not part of the page, and the keywords inside are not viewed by search engines.

The join() method joins all elements of an array into a string, and returns the string.

The elements will be separated by a specified separator. The default separator is comma (,).
Syntax:
array.join(separator)

Optional. The separator to be used. If omitted, the elements are separated with a comma

new ActiveXObject(Microsoft.XMLHTTP)
   This constructor is for Internet Explorer.

new XMLHttpRequest()
   This constructor is for any other browser including Firefox.

http.onreadystatechange

URL reqriting is Simple Rewriting Your URLS (links) Also Redirecting Them To Known URLS.e.g you’ll make the link :

view_my_profile.html –> Is Redirected to function.php?op=3