docs.sheetjs.com/docz/static/katex/contrib/copy-tex.mjs

// Set these to how you want inline and display math to be delimited.
const defaultCopyDelimiters = {
  inline: ['$', '$'],
  // alternative: ['\(', '\)']
  display: ['$$', '$$'] // alternative: ['\[', '\]']

}; // Replace .katex elements with their TeX source (<annotation> element).
// Modifies fragment in-place.  Useful for writing your own 'copy' handler,
// as in copy-tex.js.

const katexReplaceWithTex = function katexReplaceWithTex(fragment, copyDelimiters) {
  if (copyDelimiters === void 0) {
    copyDelimiters = defaultCopyDelimiters;
  }

  // Remove .katex-html blocks that are preceded by .katex-mathml blocks
  // (which will get replaced below).
  const katexHtml = fragment.querySelectorAll('.katex-mathml + .katex-html');

  for (let i = 0; i < katexHtml.length; i++) {
    const element = katexHtml[i];

    if (element.remove) {
      element.remove(null);
    } else {
      element.parentNode.removeChild(element);
    }
  } // Replace .katex-mathml elements with their annotation (TeX source)
  // descendant, with inline delimiters.


  const katexMathml = fragment.querySelectorAll('.katex-mathml');

  for (let i = 0; i < katexMathml.length; i++) {
    const element = katexMathml[i];
    const texSource = element.querySelector('annotation');

    if (texSource) {
      if (element.replaceWith) {
        element.replaceWith(texSource);
      } else {
        element.parentNode.replaceChild(texSource, element);
      }

      texSource.innerHTML = copyDelimiters.inline[0] + texSource.innerHTML + copyDelimiters.inline[1];
    }
  } // Switch display math to display delimiters.


  const displays = fragment.querySelectorAll('.katex-display annotation');

  for (let i = 0; i < displays.length; i++) {
    const element = displays[i];
    element.innerHTML = copyDelimiters.display[0] + element.innerHTML.substr(copyDelimiters.inline[0].length, element.innerHTML.length - copyDelimiters.inline[0].length - copyDelimiters.inline[1].length) + copyDelimiters.display[1];
  }

  return fragment;
};

document.addEventListener('copy', function (event) {
  const selection = window.getSelection();

  if (selection.isCollapsed) {
    return; // default action OK if selection is empty
  }

  const fragment = selection.getRangeAt(0).cloneContents();

  if (!fragment.querySelector('.katex-mathml')) {
    return; // default action OK if no .katex-mathml elements
  } // Preserve usual HTML copy/paste behavior.


  const html = [];

  for (let i = 0; i < fragment.childNodes.length; i++) {
    html.push(fragment.childNodes[i].outerHTML);
  }

  event.clipboardData.setData('text/html', html.join('')); // Rewrite plain-text version.

  event.clipboardData.setData('text/plain', katexReplaceWithTex(fragment).textContent); // Prevent normal copy handling.

  event.preventDefault();
});