opens any three.js example in codepen to play around with it.

three-example-to-codepen.js

function extractScriptContent(root) {
  return Array.from(root.querySelectorAll('script:not([src])'))
    .filter(el => !el.type || el.type.endsWith('javascript'))
    .reduce((result, el) => {
      el.parentNode.removeChild(el);
      return result + el.textContent;
    }, '');
}

function extractCssContent(root) {
  return Array.from(root.querySelectorAll('style')).reduce((result, el) => {
    el.parentNode.removeChild(el);
    return result + el.textContent;
  }, '');
}

function normalizeUrls(documentText) {
  const normalizeUrl = (() => {
    const urlHelper = document.createElement('a');

    return url => {
      urlHelper.href = url;
      return urlHelper.toString();
    };
  })();

  return documentText
    .replace(
      /(href|src)=(?:"([^"]*)"|'([^']*)')/g,
      ($0, attrName, dqValue, sqValue) =>
        `${attrName}="${normalizeUrl(sqValue || dqValue)}"`
    )
    .replace(
      /(\.\s*load\s*\(\s*')([^']*)(')/g,
      ($0, prefix, url, suffix) => prefix + normalizeUrl(url) + suffix
    );
}

async function loadExampleHtml() {
  let url = '';
  if (document.location.pathname === '/examples/') {
    url = document.location.hash.slice(1) + '.html';
  }

  return (await fetch(url)).text();
}

async function main() {
  const text = await loadExampleHtml();
  const parser = new DOMParser();
  const doc = parser.parseFromString(normalizeUrls(text), 'text/html');

  const js = extractScriptContent(doc);
  const css = extractCssContent(doc);
  const html = doc.body.innerHTML;

  const form = document.createElement('form');
  const input = document.createElement('input');

  input.type = 'hidden';
  input.name = 'data';
  input.value = JSON.stringify({html, css, js});

  form.appendChild(input);
  form.method = 'POST';
  form.action = 'https://codepen.io/pen/define';

  document.body.appendChild(form);

  form.submit();
}

main().catch(err => console.error(err));