const tldjs = require('tldjs');

tldjs.parse(undefined);
// { hostname: 'undefined',
//   isValid: true,
//   isIp: false,
//   tldExists: false,
//   publicSuffix: null,
//   domain: null,
//   subdomain: null }

const custom = tldjs.fromUserSettings({ extractHostname: (hostname) => hostname });
custom.parse(undefined)
// { hostname: undefined,
//   isValid: false,
//   isIp: false,
//   tldExists: false,
//   publicSuffix: null,
//   domain: null,
//   subdomain: null }

const URL = require('url').URL;
const tldjs = require('tldjs').fromUserSettings({ extractHostname: (url) => new URL(url).hostname });

tldjs.parse(undefined);
// Thrown:
// { TypeError [ERR_INVALID_URL]: Invalid URL: undefined
//     at onParseError (internal/url.js:241:17)
//     at new URL (internal/url.js:319:5)
//     at extractHostname (repl:1:60)
//     at Object.parse (/home/remi/dev/repositories/public/tld.js/index.js:52:17) input: 'undefined' }

tldjs.parse('https://foo.com/bar')
// { hostname: 'foo.com',
//   isValid: true,
//   isIp: false,
//   tldExists: true,
//   publicSuffix: 'com',
//   domain: 'foo.com',
//   subdomain: '' }

module.exports = function extractHostname(value) {
  if (!isNaN(value)) {
    return null;
  }
  if (typeof value !== 'string') {
    return null;
  }

  // First check if `value` is already a valid hostname.
  if (isValid(value)) {
    return trimTrailingDots(value);
  }

  var url = value;

  var needsTrimming = checkTrimmingNeeded(url);
......

tld.parse(null)
tld.parse(undefined)
tld.parse(() => {})
{
    "hostname": null,
    "isValid": false,
    "isIp": false,
    "tldExists": false,
    "publicSuffix": null,
    "domain": null,
    "subdomain": null
}

module.exports = function isValid(hostname) {
  if (!isNaN(hostname)) {
    return false;
  }
  if (typeof hostname !== 'string') {
    return false;
  }
...