JS Regex

Extract domain name in URL (with subdomains).txt

I have solved this regex problem for : 
https://www.codewars.com/kata/514a024011ea4fb54200004b
Find domain name in URLs with subdomains or without subdomains :

Regex  :  /((\w*:)?(\/\/)?(www\.)?)?([\w-]+\.)?(\w{2,}[\w-]+)\./g

  function domainName(url){
    var re = /((\w*:)?(\/\/)?(www\.)?)?([\w-]+\.)?(\w{2,}[\w-]+)\./g;

    var arr = re.exec(url);

    return arr[arr.length-1];
  }
  
  //Output:
  
http://github.com/carbonfive/raygun  ==> github
http://www.zombie-bites.com ==> zombie-bites
www.zuonegwr3vrhsjmtir07qwup.tv/default ==> uonegwr3vrhsjmtir07qwup
asdsad.wewewe-wewr.com ==> wewewe-wewr
ftp://wewe.sadg.cdfdfdgfg.co ==> cdfdfdgfg
asdsad.fgfdgf.okk.te  ==> okk
www.google.co.uk ==> google

Find domain from codewars.com

From: https://www.codewars.com/kata/514a024011ea4fb54200004b/solutions/javascript/all/best_practices

1.  

function domainName(url){
  url = url.replace("https://", '');
  url = url.replace("http://", '');
  url = url.replace("www.", '');
  return url.split('.')[0];
};

2.

function domainName(url){
  return url.match(/(?:http(?:s)?:\/\/)?(?:w{3}\.)?([^\.]+)/i)[1];
}

3.

function domainName(url){
  return url.replace(/(https?:\/\/)?(www\.)?/, '').split('.')[0]
}

4.