Youtube subtitle view (run addLyrics() function)

test.js

[
    'https://unpkg.com/codemirror@5.35.0/lib/codemirror.js',
    'https://code.jquery.com/jquery-3.3.1.min.js',
].forEach(url => {
    const script = document.createElement('script');
    script.src = url;
    document.head.appendChild(script);
});

[
    'https://unpkg.com/codemirror@5.35.0/lib/codemirror.css',
].forEach(url => {
    const link = document.createElement('link');
    link.href = url;
    link.rel  = 'stylesheet';
    document.head.appendChild(link);
});


function YTLyrics(vId, lang) {
    lang = lang || 'en';
    if (!vId) {
        const query = location.search.substr(1).split('&')
            .reduce((obj, v) => {
                const pair = v.split('=');
                obj[pair[0]] = pair[1];
                return obj;
            }, {});
        vId = query.v;
    }
    const url = `https://video.google.com/timedtext?lang=${lang}&name=&v=${vId}`;
    return fetch(url)
        .then(response => response.text())
        .then(str => (new window.DOMParser()).parseFromString(str, "text/xml"))
        .then(data => data.getElementsByTagName('text'))
        .then((collection) => {
            let lyrics = '';
            for (let i = 0; i < collection.length; i += 1) {
                lyrics += `${collection.item(i).innerHTML}\n`;
            }
            return lyrics;
        });
}

function addLyrics() {
    if (!document.getElementById('lyrics-view')) {
        jQuery('#player-ads').before('<div id="lyrics-view" style="font-size: 1.7rem"><div>');
    }
    YTLyrics()
    .then(str => {
        CodeMirror(document.getElementById('lyrics-view'), { lineNUmbers: true, value: str });
    }).catch(err => {
        console.error(err);
    });
}