MutationObserver

// 
const targetNode = document.getElementById("some-id");

// 
const config = { attributes: true, childList: true, subtree: true };

// 
const callback = function (mutationsList, observer) {
  // Use traditional 'for loops' for IE 11
  for (let mutation of mutationsList) {
    if (mutation.type === "childList") {
      console.log("A child node has been added or removed.");
    } else if (mutation.type === "attributes") {
      console.log("The " + mutation.attributeName + " attribute was modified.");
    }
  }
};

// 
const observer = new MutationObserver(callback);

// 
observer.observe(targetNode, config);

// 
observer.disconnect();