Replacement for querySelector("::slotted(x)")

query-slotted.js

function querySlotted(root, selector) {
  let slots = root.querySelectorAll('slot');
  let matched = [];
  slots.forEach((slot) => {
    matched = matched.concat(slot.assignedNodes().filter((el) => {
      return el.matches(selector);
    }));
  });
  return matched;
}

You can use slot.assignedElements to prevent testing selector on Text nodes.

Marvelous, thank you very much!