How i can get the domain name example.com
from the set of possible subdomains sub1.example.com
sub2.example.com
sub3.example.com
using javascript ...?
var parts = location.hostname.split('.');
var subdomain = parts.shift();
var upperleveldomain = parts.join('.');
To get only the second-level-domain, you might use
var parts = location.hostname.split('.');
var sndleveldomain = parts.slice(-2).join('.');