const cache = new Map();

const setCallback = (element, key) => {
  if (cache.has(key)) {
    return cache.get(key);
  }

  throw element;
};

const asyncElement = new Promise(res => {
  setTimeout(() => {
    res("Mikita");
  }, 1000);
});

const render = () => {
  const root = document.querySelector("#app");
  if (root.firstChild) {
    root.firstChild.remove();
  }
  const element = document.createElement("div");
  let text = "loading...";
  try {
    text = setCallback(asyncElement, "name");
  } catch (promise) {
    promise.then(data => {
      cache.set("name", data);
      render()
    });
  }

  element.textContent = text;
  root.appendChild(element);
};

render();