document.addEventListener("DOMContentLoaded", () => {
  // current page URL
  let url = window.location.href; 

  // replace `/html/` with `/markdown/`
  url = url.replace("/html/", "/markdown/");

  // replace `.html` with `.md`
  url = url.replace(/\.html$/, ".md");

  // assign to <a>
  const a = document.getElementById("download-md");
  a.href = url;

  // suggest filename
  const filename = url.split("/").pop(); // e.g. markdowntest.md
  a.download = filename;
});