"Load More" Button for Blog Archives

<script>
(function () {
    var containerSel = '.wp-block-post-template, #main, .site-main';
    var itemSel = '.wp-block-post-template > li, article.post, article.type-post';
    var nextSel = '.wp-block-query-pagination-next, .nav-links a.next, a.next.page-numbers';
    var pagerSel = '.wp-block-query-pagination, .navigation.pagination, .nav-links';
    var next = document.querySelector(nextSel);
    var container = document.querySelector(containerSel);
    if (!next || !container || !window.fetch || !window.DOMParser) { return; }
    var pager = next.closest(pagerSel) || next.parentNode;
    var button = document.createElement('button');
    button.type = 'button';
    button.className = 'wp-element-button wpide-load-more';
    button.textContent = 'Load more posts';
    button.style.cssText = 'display:block;margin:2em auto;';
    var status = document.createElement('p');
    status.className = 'screen-reader-text';
    status.setAttribute('aria-live', 'polite');
    pager.parentNode.insertBefore(button, pager);
    pager.parentNode.insertBefore(status, pager);
    pager.style.display = 'none';
    var url = next.href;
    button.addEventListener('click', function () {
        button.disabled = true;
        button.textContent = 'Loading…';
        fetch(url, { credentials: 'same-origin' }).then(function (r) { return r.text(); }).then(function (html) {
            var doc = new DOMParser().parseFromString(html, 'text/html');
            var items = doc.querySelectorAll(itemSel);
            var current = container.querySelectorAll(itemSel);
            var anchor = current[current.length - 1];
            items.forEach(function (item) {
                var node = document.importNode(item, true);
                if (anchor) { anchor.parentNode.insertBefore(node, anchor.nextSibling); anchor = node; } else { container.appendChild(node); }
            });
            status.textContent = items.length + ' more posts loaded';
            var more = doc.querySelector(nextSel);
            if (more && more.href) {
                url = more.href;
                button.disabled = false;
                button.textContent = 'Load more posts';
            } else {
                button.remove();
            }
        }).catch(function () {
            window.location.href = url;
        });
    });
})();
</script>