redirect GitHub page <---> GitHub repo page

main.js

(() => {
  if (location.hostname === 'github.com') {
    const [_, username, repo] = location.pathname.split('/');
    location.href = `https://${username}.github.io/${repo}`;
    return;
  }
  if (location.hostname.includes('github.io')) {
    const username = location.host.split('.')[0];
    const repo = location.pathname.split('/')[1];
    location.href = `https://github.com/${username}/${repo}`;
    return;
  }
})();