hugo-book-theme/layouts/shortcodes/mermaid.html

{{ if not (.Page.Scratch.Get "mermaid") }}
<!-- Include mermaid only first time -->
<script src="{{ "mermaid.min.js" | relURL }}"></script>
{{ with resources.Get "mermaid.json" }}
  <script>mermaid.initialize({{ .Content | safeJS }})</script>
{{ end }}
{{ .Page.Scratch.Set "mermaid" true }}
{{ end }}

<p class="mermaid{{ with .Get "class" }} {{ . }}{{ end }}">
  {{- .Inner -}}
</p>