Document: referrer property

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 href of the parent's Window.location in same-origin requests. In cross-origin requests, it's the origin of the parent's Window.location by default. For more information, see the Referrer-Policy: strict-origin-when-cross-origin documentation.

The following will log a string containing the document's referrer.

console.log(document.referrer);

If the user navigated to the page via a link like <a href="https://www.w3.org/">W3</a>, then it will output the previous domain like developer.mozilla.org. If the user navigated to the page directly, it will output an empty string.