Polymer.Element without ShadowDOM but support slots

polymer-slot-without-shadowdom.js

class LightDom extends Polymer.Element {
  _attachDom(dom) {
    const slots = dom.querySelectorAll('slot[name]');

    slots.forEach((slot) => {
      const name = slot.getAttribute('name');

      const tmpl = this.querySelector(`[slot=${name}]`);

      if (tmpl) {
        slot.parentNode.replaceChild(tmpl, slot);
      }
    });

    const slot = dom.querySelector('slot:not([name])');

    if (slot) {
      this.childNodes.forEach(e => {
        slot.parentNode.insertBefore(e, slot.nextSibling);
      });

      slot.parentNode.removeChild(slot);
    } else {
      this.childNodes.forEach(e => {
        this.removeChild(e);
      });
    }

    this.appendChild(dom);
  }
}