Get FQDN with Regex

get-fqdn.js

/**
* Get FQDN from a string
* @name FQDN
* @param URL {String} - String you want get FQDN
* @return {String}
**/
function FQDN(URL = '') {
    URL = URL.subtring(0, 50); // This will avoid evaluate long malicious fqdn
    const regex = /[a-zA-Z0-9][a-zA-Z0-9-]{1,61}[a-zA-Z0-9](?:\.[a-zA-Z]{2,})+/i;
    const filtered = regex.exec(URL);
    if (!filtered) throw new Error(`Input ${URL} is not a valid URL.`);
    const [domain] = (Array.isArray(filtered)) ? filtered : [];
    return domain;
}