h1 links

script.js

function addLinks() {
  Array.from(document.querySelectorAll("[id]")).forEach((e) => {
    const a = document.createElement("a");
    a.href = `#${e.id}`;
    e.parentNode.replaceChild(a, e);
    a.appendChild(e);
  });
}

if (document.readyState === "complete" || document.readyState === "loaded") {
  addLinks();
} else {
  window.addEventListener("DOMContentLoaded", addLinks);
}