https://engineering.hexacta.com/didact-instances-reconciliation-and-virtual-dom-9316d650f1d0

render.js

function instantiate(element) {
  const { type, props } = element;

  // Create DOM element
  const isTextElement = type === "TEXT ELEMENT";
  const dom = isTextElement
    ? document.createTextNode("")
    : document.createElement(type);

  updateDomProperties(dom, [], props);

  // Instantiate and append children
  const childElements = props.children || [];
  const childInstances = childElements.map(instantiate);
  const childDoms = childInstances.map(childInstance => childInstance.dom);
  childDoms.forEach(childDom => dom.appendChild(childDom));

  const instance = { dom, element, childInstances };
  return instance;
}

function updateDomProperties(dom, prevProps, nextProps) {
  const isEvent = name => name.startsWith("on");
  const isAttribute = name => !isEvent(name) && name != "children";

  // Remove event listeners
  Object.keys(prevProps).filter(isEvent).forEach(name => {
    const eventType = name.toLowerCase().substring(2);
    dom.removeEventListener(eventType, prevProps[name]);
  });

  // Remove attributes
  Object.keys(prevProps).filter(isAttribute).forEach(name => {
    dom[name] = null;
  });

  // Set attributes
  Object.keys(nextProps).filter(isAttribute).forEach(name => {
    dom[name] = nextProps[name];
  });

  // Add event listeners
  Object.keys(nextProps).filter(isEvent).forEach(name => {
    const eventType = name.toLowerCase().substring(2);
    dom.addEventListener(eventType, nextProps[name]);
  });
}