Mermaid.js is a great tool to make diagrams in plain text, I use it a lot and I wanted to have a way to see previews of the code I was writing.
There are some options to do that but they require to have a mermaid-cli installed, which requires nodejs as well.
Emacs has a built-in webkit browser, in case it was compiled with --with-xwidgets flag, and mermaid run on js so it should be possible to just run the code I want in the browser and see it there.
This function makes the magic, it just take a region previously selected, which have the mermaid code, create a temp file and write some HTML there(including our mermaid code).
(defun my/preview-mermaid ()
"Render region inside a webit embebed browser."
(interactive)
(unless (region-active-p)
(user-error "Select a region first"))
(let* ((path (concat (make-temp-file (temporary-file-directory)) ".html"))
(mermaid-code (buffer-substring-no-properties (region-beginning) (region-end))))
(save-excursion
(with-temp-buffer
(insert "<body>
<pre class=\"mermaid\">")
(insert mermaid-code)
;; js script copied from mermaid documentation
(insert "</pre>
<script type=\"module\">
import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs';
mermaid.initialize({ startOnLoad: true });
</script>
</body>")
(write-file path)))
(xwidget-webkit-browse-url (format "file://%s" path))))Demo
