The hostname property of the Location interface is a string containing either the domain name or IP address of the location URL. If the URL does not have a hostname, this property contains an empty string, "". IPv4 and IPv6 addresses are normalized, such as stripping leading zeros, and domain names are converted to IDN.
See URL.hostname for more information.
A string.
console.log(window.location.hostname);
// developer.mozilla.org
const anchor = document.createElement("a");
anchor.href = "https://developer.mozilla.org:4097/";
console.log(anchor.hostname === "developer.mozilla.org");
// The port number is not included in hostname