complement title on reader of publus.jp for UserScript

pubrasche.user.js

// ==UserScript==
// @name        Pubrasche
// @namespace   https://noromanba.github.com
// @description complement title on reader of publus.jp for UserScript
// @include     *://jumpbookstore.com/client_info/SHUEISHA/html/player/viewer.html*
// @grant       none
// @noframes
// @run-at      document-end
// @version     2018.8.8.1
// @homepage    https://gist.github.com/noromanba/c2f24e19ae24ac5b6a1e6f578ca98191
// @downloadURL https://gist.github.com/noromanba/c2f24e19ae24ac5b6a1e6f578ca98191/raw/pubrasche.user.js
// @license     MIT License https://nrm.mit-license.org/2018
// @author      noromanba   https://noromanba.github.com
// @icon        https://upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Maki-parking-garage-11.svg/1000px-Maki-parking-garage-11.svg.png
// ==/UserScript==

// Icon (CC0 by samanpwbb; Mapbox)
// https://commons.wikimedia.org/wiki/File%3AMaki-parking-garage-11.svg
//  https://github.com/mapbox/maki/blob/master/icons/parking-garage-11.svg

// Devel
// https://gist.github.com/noromanba/c2f24e19ae24ac5b6a1e6f578ca98191

// https://publus.jp/reader/
(() => {
    'use strict';

    const observer = new MutationObserver(records => {
        records.forEach(record => {
            const node = record.target;
            if (!node.title) return;

            document.title = `${node.title} - ${document.title}`;
            observer.disconnect();
        });
    });

    observer.observe(document.body.querySelector([
        '#pagetitle',
    ]), { attributes: true, attributeFilter: ['title',], });
})();