Document.domain

var domainString = document.domain;
document.domain = string;

Доменная часть источника происхождения (origin) текущего документа.

SecurityError

An attempt has been made to set domain under one of the following conditions:

• The document is inside a sandboxed <iframe>
• The document has no browsing context
• The document's effective domain is null
• The given value is not equal to the document's effective domain (or it is not a registerable domain suffix of it)
• The document-domain Feature-Policy is enabled

For the URI http://developer.mozilla.org/ru/docs/Web, this example sets currentDomain to the string "developer.mozilla.org".

var currentDomain = document.domain;

If a document, such as www.example.xxx/good.html, has the domain of "www.example.xxx", this example attempts to close the window.

var badDomain = "www.example.xxx";

if (document.domain == badDomain) {
  // Just an example: window.close() sometimes has no effect
  window.close();
}

• Политика одинакового источника
• Location.hostname
• Location.host
• Window.origin