Wikipedia: сворачиваемые разделы статьи

// Click any H2 heading to collapse or expand its section
function setupCollapse() {
  const headings = document.querySelectorAll('.mw-parser-output > .mw-heading2, .mw-parser-output > h2');
  headings.forEach(function (h) {
    if (h.dataset.jzCollapse) { return; }
    h.dataset.jzCollapse = '1';
    h.style.cursor = 'pointer';
    h.title = 'Click to collapse or expand this section';
    h.addEventListener('click', function (e) {
      if (e.target.tagName === 'A') { return; }
      let el = h.nextElementSibling;
      const hidden = h.dataset.jzHidden === '1';
      while (el && !/^H2$/.test(el.tagName) && !el.classList.contains('mw-heading2')) {
        el.style.display = hidden ? '' : 'none';
        el = el.nextElementSibling;
      }
      h.dataset.jzHidden = hidden ? '0' : '1';
      h.style.opacity = hidden ? '1' : '0.6';
    });
  });
}
setupCollapse();
new MutationObserver(setupCollapse).observe(document.body, { childList: true, subtree: true });