Subdomain extractor

RealmManager.js

function getRealmIdentifier(hostname, {defaultIdentifier = "gdis", baseDomain = "example.local"} = {}, debug = false) {
  const _baseDomain = baseDomain.replace('.', '\\.');
  const pattern = new RegExp(`^(?:www\\.)?([^:\\/?\\n\\.]+)\\.${baseDomain}$`, 'i');
  const result = hostname.match(pattern);

  debug && console.info(hostname, defaultIdentifier, baseDomain, pattern, result);

  if (result === null) {
    return defaultIdentifier;
  }

  const [_, subdomain] = result;
  return subdomain;
};

console.info(getRealmIdentifier("www.gdis.example.local") === "gdis");
console.info(getRealmIdentifier("gdis.example.local") === "gdis");
console.info(getRealmIdentifier("dcwc.example.local") === "dcwc");
console.info(getRealmIdentifier("www.dcwc.example.local") === "dcwc");
console.info(getRealmIdentifier("www.dcwc.example.org", {baseDomain: "example.org"}) === "dcwc");
console.info(getRealmIdentifier("www.dcwc.staging.example.org", {baseDomain: "staging.example.org"}) === "dcwc");