document.domain

Gets/sets the domain portion of the origin of the current document, as used by the same origin policy.

Syntax

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

Example

// for document www.example.xxx/good.html,
// this script closes the window
var badDomain = "www.example.xxx";

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

// For the URI http://developer.mozilla.org/en-US/docs/Web the
// following sets domain to the string "developer.mozilla.org"
var domain = document.domain;

Notes

This property returns null if the domain of the document cannot be identified.

Mozilla will let you set it to a superdomain of the current value, constrained by its base domain. For example, on developer.mozilla.org it is possible to set it to "mozilla.org" but not "mozilla.com" or "org".

If this property is successfully set, the port part of the origin is also set to null.

Mozilla distinguishes a document.domain property that has never been set from one explicitly set to the same domain as the document's URL, even though the property returns the same value in both cases. One document is allowed to access another if they have both set document.domain to the same value, indicating their intent to cooperate, or neither has set document.domain and the domains in the URLs are the same (implementation). Were it not for this special policy, every site would be subject to XSS from its subdomains (for example, https://bugzilla.mozilla.org could be attacked by bug attachments on https://bug*.bugzilla.mozilla.org).

Specification

• DOM Level 2 HTML: document.domain (describes it as read-only)
• HTML5: document.domain (describes behavior similar to Mozilla's)

See also

• Same origin policy for JavaScriptHTML