clone-with-shadow-roots.js

/**
 * cloneNode(true), but also clones shadow roots.
 * @param {Element}
 * @param {ShadowRoot[]} [shadowRoots] Any closed shadow roots passed here will be included.
 */
function cloneWithShadowRoots(node, shadowRoots) {
  function walk(node, clone) {
    let shadow = node.shadowRoot || shadowRoots.find(r => r.host === node);
    if (shadow) {
      clone.attachShadow({ mode: shadow.mode }).append(...[].map.call(shadow.childNodes, c => c.cloneNode(true)));
    }
    for (let i=0; i<node.children.length; i++) walk(node.children[i], clone.children[i]);
  }
  const clone = node.cloneNode(true);
  walk(node, clone);
  return clone;
}