function getDomainName( hostname ) {
var TLDs = new RegExp(/\.(com|net|org|biz|ltd|plc|edu|mil|asn|adm|adv|arq|art|bio|cng|cnt|ecn|eng|esp|etc|eti|fot|fst|g12|ind|inf|jor|lel|med|nom|ntr|odo|ppg|pro|psc|psi|rec|slg|tmp|tur|vet|zlg|asso|presse|k12|gov|muni|ernet|res|store|firm|arts|info|mobi|maori|iwi|travel|asia|web|tel)(\.[a-z]{2,3})?$|(\.[^\.]{2,3})(\.[^\.]{2,3})$|(\.[^\.]{2})$/);
return hostname.replace(TLDs, '').split('.').pop();
}
/*** TEST ***/
var domains = [
'domain.com',
'subdomain.domain.com',
'www.subdomain.domain.com',
'www.subdomain.domain.info',
'www.subdomain.domain.info.xx',
'mail.subdomain.domain.co.uk',
'mail.subdomain.domain.xxx.yy',
'mail.subdomain.domain.xx.yyy',
'mail.subdomain.domain.xx',
'domain.xx'
];
var result = [];
for (var i = 0; i < domains.length; i++) {
result.push( getDomainName( domains[i] ) );
}
alert ( result.join(' | ') );
// result: domain | domain | domain | domain | domain | domain | domain | domain | domain | domain