HTMLSlotElement: assignedElements() method

The assignedElements() method of the HTMLSlotElement interface returns a sequence of the elements assigned to this slot (and no other nodes).

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

assignedElements()
assignedElements(options)

let slots = this.shadowRoot.querySelector("slot");
let elements = slots.assignedElements({ flatten: true });