The assignedNodes() method of the HTMLSlotElement interface returns a sequence of the nodes assigned to this slot.

If the flatten option is set to true, it returns a sequence of both the nodes assigned to this slot, as well as the nodes assigned to any other slots that are descendants of this slot. If no assigned nodes are found, it returns the slot's fallback content.

options Optional

An object that sets options for the nodes to be returned. The available options are:

flatten

A boolean value indicating whether to return the assigned nodes of any available child <slot> elements (true) or not (false). Defaults to false.

An array of nodes.

The following snippet is taken from our slotchange example (See it live).

let slots = this.shadowRoot.querySelectorAll("slot");
slots[1].addEventListener("slotchange", (e) => {
  let nodes = slots[1].assignedNodes();
  console.log(
    `Element in Slot "${slots[1].name}" changed to "${nodes[0].outerHTML}".`,
  );
});

Here we grab references to all the slots, then add a slotchange event listener to the 2nd slot in the template — which is the one that keeps having its contents changed in the example.

Every time the element inserted in the slot changes, we log a report to the console saying which slot has changed, and what the new node inside the slot is.