Locked Topic Quotes (SMF v2; non-working)

// ==UserScript==
// @name         Locked topic quotes
// @namespace    https://foxscotch.us/
// @version      1.3
// @description  Show quote buttons on locked topics
// @author       Foxscotch
// @match        https://forum.blockland.us/index.php?topic=*
// @grant        none
// ==/UserScript==
'use strict';

var mainUrl = 'https://forum.blockland.us/index.php?';

function getQuote(link) {
    window.ajax_indicator(true);
    var xhr = new XMLHttpRequest();
    var quote;

    xhr.onload = function () {
        var xml = xhr.responseXML;
        quote = xml.getElementsByTagName('quote')[0].textContent;

        console.log(xml);

        document.getElementById('locked-topic-textbox').value += quote;

        window.ajax_indicator(false);
    };

    xhr.open('GET', mainUrl + `action=quotefast;quote=${link.dataset.messageId};xml`);
    xhr.send();
}

function addTextBox() {
    var container = document.createElement('div');
    container.id = 'locked-topic-container';

    var textArea = document.createElement('textarea');
    textArea.id = 'locked-topic-textbox';

    var copyButton = document.createElement('button');
    copyButton.id = 'locked-topic-copy';
    copyButton.textContent = "Copy to clipboard";

    container.style.margin = 'auto';
    container.style.width = '25%';

    textArea.style.display = 'block';
    textArea.style.height = '150px';
    textArea.style.width = "100%";

    copyButton.addEventListener('click', function () {
        textArea.select();
        var copied = document.execCommand('copy');
        copied ? console.log('Copied') : console.log('Not copied');
    });

    var nav = document.getElementsByClassName('navigate_section')[1];
    nav.parentElement.insertBefore(container, nav);
    container.appendChild(copyButton);
    container.appendChild(textArea);
}

function addQuoteButtons() {
    var msgIdRegex = /.+msg(\d+)/;
    var destinations = document.querySelectorAll('div.flow_hidden');

    for (var dest of destinations) {
        var ul = document.createElement('ul');
        ul.classList.add('reset', 'smalltext', 'quickbuttons');

        var li = document.createElement('li');
        li.classList.add('quote_button');
        ul.appendChild(li);

        var a = document.createElement('a');
        a.href = '#locked-topic-textbox';
        a.textContent = 'Quote';
        li.appendChild(a);

        dest.appendChild(ul);

        var msgIdLink = dest.querySelector('a').href;
        a.dataset.messageId = msgIdLink.match(msgIdRegex)[1];

        a.addEventListener('click', getQuote.bind(null, a));
    }
}

var topic_image = document.querySelectorAll('h3.catbg > img')[0];
if (topic_image && topic_image.src.includes('locked')) {
    addTextBox();
    addQuoteButtons();
}