Finds all elements on the page, including those within shadow dom.

findall_elements_deep.js

/**
 * @author ebidel@ (Eric Bidelman)
 * License Apache-2.0
 */

/**
 * Finds all elements on the page, inclusive of those within shadow roots.
 * @param {string=} selector Simple selector to filter the elements by. e.g. 'a', 'div.main'
 * @return {!Array<string>} List of anchor hrefs.
 */
function collectAllElementsDeep(selector = null) {
  const allElements = [];

  const findAllElements = function(nodes) {
    for (let i = 0, el; el = nodes[i]; ++i) {
      allElements.push(el);
      // If the element has a shadow root, dig deeper.
      if (el.shadowRoot) {
        findAllElements(el.shadowRoot.querySelectorAll('*'));
      }
    }
  };

  findAllElements(document.querySelectorAll('*'));

  return selector ? allElements.filter(el => el.matches(selector)) : allElements;
}