findNcxPath(manifestNode, spineNode) {
    // var node = manifestNode.querySelector("item[media-type='application/x-dtbncx+xml']");
    var node = Object(core["qsp"])(manifestNode, "item", {
      "media-type": "application/x-dtbncx+xml"
    });
    var tocId; // If we can't find the toc by media-type then try to look for id of the item in the spine attributes as
    // according to http://www.idpf.org/epub/20/spec/OPF_2.0.1_draft.htm#Section2.4.1.2,
    // "The item that describes the NCX must be referenced by the spine toc attribute."

    if (!node) {
      tocId = spineNode.getAttribute("toc");

      if (tocId) {
        // node = manifestNode.querySelector("item[id='" + tocId + "']");
        node = manifestNode.querySelector(`#${tocId}`);
      }
    }

    return node ? node.getAttribute("href") : false;
  }
Find TOC NCX
media-type="application/x-dtbncx+xml" href="toc.ncx"
@private
@param {element} manifestNode
@param {element} spineNode
@return {string}