Handling dynamic content with greasemonkey

main.js

// ==UserScript==
// @name     Apply rules to dynamically loaded content
// @version  1
// @grant    none
// ==/UserScript==

// Create a new mutation observer
const observer = new window.MutationObserver(() => {
  // Apply your rules here
  
  // Example: hide tweet stats on twitter
  document.querySelectorAll('div[data-testid="reply"]')
    .forEach(v => v.parentElement.parentElement.style["display"] = "none");
});
observer.observe(document, { subtree: true, childList: true });