hugo-geekdoc/src/js/copycode.js

function createCopyButton(highlightDiv) {
  const button = document.createElement("span");

  if (highlightDiv.querySelector(".lntable")) {
    selector = ".lntable .lntd:last-child pre > code";
  } else {
    selector = "pre > code";
  }

  const codeToCopy = highlightDiv.querySelector(selector).innerText.trim();

  button.classList.add(
    "flex",
    "align-center",
    "justify-center",
    "clip",
    "gdoc-post__codecopy"
  );
  button.type = "button";
  button.innerHTML =
    '<svg class="icon copy"><use xlink:href="#gdoc_copy"></use></svg>' +
    '<svg class="icon check hidden"><use xlink:href="#gdoc_check"></use></svg>';
  button.setAttribute("data-clipboard-text", codeToCopy);
  button.setAttribute("data-copy-feedback", "Copied!");
  button.setAttribute("role", "button");
  button.setAttribute("aria-label", "Copy");

  highlightDiv.classList.add("gdoc-post__codecontainer");
  highlightDiv.insertBefore(button, highlightDiv.firstChild);
}

document
  .querySelectorAll(".highlight")
  .forEach((highlightDiv) => createCopyButton(highlightDiv));