Lazy-load-magic

function* findLazyElements() {
  const blocks = [
    ...Array.from(document.querySelectorAll("noscript.lazyload")).map(lazy =>
      parseHTML(lazy.innerText).map(elem => ({ elem, parent: lazy.parentNode }))
    ),
    ...Array.from(document.querySelectorAll("template.lazyload")).map(lazy =>
      Array.from(lazy.content.cloneNode(true).children)
        .map(elem => ({ elem, parent: lazy.parentNode }))
        .map(item => {
          if (item.elem.tagName !== "SCRIPT") return item;
          item.elem = Object.assign(item.elem.cloneNode(true), {
            async: false
          });
          return item;
        })
    )
  ];

  for (const block of blocks) {
    yield* block;
  }
}

function parseHTML(html) {
  const div = document.createElement("div");
  div.innerHTML = html;
  return Array.from(div.children);
}

const it = findLazyElements();
requestIdleCallback(function f() {
  const { value, done } = it.next();
  if (done) return;
  value.parent.appendChild(value.elem);
  requestIdleCallback(f);
});