How to tell when a dynamically created element has rendered

Question

I need to accurately measure the dimensions of text within my web app, which I am achieving by creating an element (with relevant CSS classes), setting its innerHTML

Answer 1

According to @Elliot B.'s answer, I made a plan that suits me.

const callback = () => {
  const el = document.querySelector('#a');
  if (el) {
    observer.disconnect();
    el.addEventListener('click', () => {});
  }
};

const observer = new MutationObserver(callback);
observer.observe(document.body, { subtree: true, childList: true });