render.js

function render(rootDom, element) {
  const { type, props } = element;
  const dom = document.createElement(type);
  Object.keys(props).filter(isAttribute).forEach(name => {
    dom[name] = props[name];
  });
  const children = props.children || [];
  children.forEach(childElement => render(dom, childElement));
  rootDom.appendChild(dom);
}

const isAttribute = name => name != "children";