Materialize/doc/user/layouts/partials/sidebar.html

<div class="sidebar-wrapper">
  {{ $currentPage := . }}
  <nav role="navigation" class="sidebar">
    <ul>
      <div id="docsearch"></div>
      <select id="version-select" class="version-dropdown" style="width: 100%; box-sizing: border-box;">
      </select>
      <br><br>

      {{ range .Site.Menus.main.ByWeight }}
      <li class="level-1 {{if .HasChildren }}has-children{{ else }}no-children{{ end }}">
          <a {{with .URL}}href="{{.}}"{{end}} class="{{if $currentPage.IsMenuCurrent "main" .}}active{{end}}">
            {{- if .HasChildren }}
              {{ readFile "static/images/icon_sidebar_expander.svg" | safeHTML }}
            {{ end }}
            {{.Name | markdownify}}
          </a>

        {{- if .HasChildren }}
        <ul>
          {{- range .Children }}
          <li class="level-2 {{if .HasChildren }}has-children{{ else }}no-children{{ end }}">
            <a {{with .URL}}href="{{.}}"{{end}} class="{{if $currentPage.IsMenuCurrent "main" .}}active{{end}}">
              {{- if .HasChildren }}
                {{ readFile "static/images/icon_sidebar_expander.svg" | safeHTML }}
              {{ end }}
              {{.Name | markdownify}}
            </a>

            {{- if .HasChildren }}
            <ul>
              {{- range .Children }}
              <li class="level-3 {{if .HasChildren }}has-children{{ else }}no-children{{ end }}">
                <a {{with .URL}}href="{{.}}"{{end}} class="{{if $currentPage.IsMenuCurrent "main" .}}active{{end}}">
                  {{- if .HasChildren }}
                    {{ readFile "static/images/icon_sidebar_expander.svg" | safeHTML }}
                  {{ end }}
                  {{.Name | markdownify}}
                </a>

                {{- if .HasChildren }}
                <ul>
                  {{- range .Children }}
                  <li class="level-4">
                    <a href="{{.URL}}" class="{{if $currentPage.IsMenuCurrent "main" .}}active{{end}}">
                      {{.Name | markdownify}}
                    </a>
                  </li>
                  {{- end}}
                </ul>
                {{- end}}
              </li>
              {{- end}}
            </ul>
            {{- end}}
          </li>
          {{- end}}
        </ul>
        {{- end}}
      </li>
      {{- end}}
    </ul>
  </nav>
  <button class="close-topics" aria-label="Close the topics sidebar">
    <svg xmlns="http://www.w3.org/2000/svg" class="ionicon" viewBox="0 0 512 512"><title>Close</title><path fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="32" d="M368 368L144 144M368 144L144 368"/></svg>
  </button>
</div>

<script>
  document.addEventListener('DOMContentLoaded', function () {
    const versionSelect = document.getElementById('version-select');
    const currentPath = window.location.pathname;

    fetch('/docs/versions.json')
      .then( response => {
        if (!response.ok) {
          throw new Error('File not found');
        }
        return response.json();
      })
      .catch(() => {
        return fetch('{{ .Site.BaseURL }}versions.json')
          .then(response => {
            if (!response.ok) {
              throw new Error('Fallback file not found');
            }
            return response.json();
          });
      })
      .then(versions => {
        versions.forEach(version => {
          const option = document.createElement('option');
          option.value = version.base_url;
          option.textContent = version.name;
          versionSelect.appendChild(option);
        });

        const currentVersion = versions.filter(version => currentPath.includes(version.base_url))?.at(-1)?.base_url;

        if (currentVersion) {
          versionSelect.value = currentVersion;
        }

        versionSelect.addEventListener('change', function () {
          const baseUrl = '{{ .Site.BaseURL }}';
          const strippedBaseUrl = baseUrl.endsWith(currentVersion) ? baseUrl.slice(0, -currentVersion.length) : baseUrl;
          const selectedBaseUrl = strippedBaseUrl + versionSelect.value;
          if (selectedBaseUrl) {
            window.location.href = selectedBaseUrl;
          }
        });
      })
      .catch(error => console.error('Error fetching versions:', error));
  });
</script>