html

<button id="add-nodes">Add a node</button>
<button id="set-attribute">Change the color</button>

<button id="reset">Reset</button>

<pre id="log">Mutation type:</pre>
<div id="target"><p>Node #0</p></div>

js

const addNodes = document.querySelector("#add-nodes");
const setAttribute = document.querySelector("#set-attribute");
const reset = document.querySelector("#reset");
const log = document.querySelector("#log");
const target = document.querySelector("#target");
let nodeNumber = 1;

addNodes.addEventListener("click", () => {
  const newPara = document.createElement("p");
  newPara.textContent = `Node #${nodeNumber}`;
  nodeNumber++;
  target.appendChild(newPara);
});

setAttribute.addEventListener("click", () => {
  if (target.getAttribute("class") === "red") {
    target.setAttribute("class", "blue");
  } else {
    target.setAttribute("class", "red");
  }
});

reset.addEventListener("click", () => self.location.reload());

function logMutationType(records) {
  for (const record of records) {
    log.textContent = `Mutation type: ${record.type}`;
  }
}

const observer = new MutationObserver(logMutationType);
observer.observe(target, { childList: true, attributes: true, subtree: true });