observe element

function observeElement(element, callback) {
  const config = {
    attributes: true,
    childList: true,
    subtree: true,
    attributeOldValue: true,
  };

  const listener = function (mutationsList, observer) {
    for (const mutation of mutationsList) {
      let type = mutation.type === 'childList' ? 'content' : mutation.type;
      let oldValue = mutation.oldValue;
      let newValue = null;

      if (mutation.type === 'childList') {
        newValue = [...mutation.target.childNodes].map((node) => {
          return node.nodeName === '#text' ? node.nodeValue : node;
        });
      } else if (mutation.type === 'attributes') {
        newValue = mutation.target.getAttribute(mutation.attributeName)
      }
      
      callback({type, oldValue, newValue});
    }
  };

  const observer = new MutationObserver(listener);

  observer.observe(element, config);

  return () => observer.disconnect();
}