const { JSDOM } = require("jsdom");
const options = {};
const dom = new JSDOM("", options);
const window = dom.window;
const document = window.document;

document.open();

const observer = new window.MutationObserver(records =>
  records.forEach(record => console.log(formatMutationRecord(record)))
);

observer.observe(document, {
  attributes: true,
  attributeOldValue: true,
  characterData: true,
  characterDataOldValue: true,
  childList: true,
  subtree: true
});

document.write("a b c d");

document.close();

function formatMutationRecord(record) {
  const { target, oldValue } = record;

  switch (record.type) {
    case "characterData": {
      return target.nodeName + ": " + JSON.stringify(oldValue) + " => " + JSON.stringify(target.nodeValue);
    }

    case "childList": {
      const { addedNodes } = record;
      return "inserted " + Array.from(addedNodes).map(added => added.nodeName).join(", ")
    }
  }
}