layouts/404.html

{{ define "main"}}
<script>
  var reg = /\/docs\/[a-zA-Z\-]+\/([\w|\.]+)\//;
  var res = reg.exec(location.href);
  var version = res && res[1];
  if (version === 'latest') {
    var newUrl = location.href.replace('/latest/', '/next/');
    window.location.href = newUrl
  }
</script>
<main id="main">
  <div class="mt-4 text-center">
    <h1 id="title">Not found</h1>
    <p>Oops! This page doesn't exist. Try going back to our <a href="{{ "/" | relURL }}">home page</a>.</p>
  </div>
</main>
{{ end }}