Document.referrer

The Document.referrer property returns the URI of the page that linked to this page.

The value is an empty string if the user navigated to the page directly (not through a link, but, for example, by using a bookmark). Because this property returns only a string, it doesn't give you document object model (DOM) access to the referring page.

Inside an <iframe>, the Document.referrer will initially be set to the same value as the href of the parent window's Window.location.