HTMLLinkElement: relList property

The HTMLLinkElement.relList read-only property reflects the rel attribute. It is a live DOMTokenList containing the set of link types indicating the relationship between the resource represented by the <link> element and the current document.

The property itself is read-only, meaning you can not substitute the DOMTokenList by another one, but the content of the returned list can be changed.

const links = document.getElementsByTagName("link");
for (const link of links) {
  console.log("New link found.");
  link.relList.forEach((relEntry) => {
    console.log(relEntry);
  });
}