TCBarrett

<p>This plugin requires is just the front end javascript library, the following two things to be done in support:<br />
1. Add the class ‘simpleajaxform’ to your form.<br />
2. Make sure you have the correct wp_ajax handler hook defined.</p>
<p>It was primarily built as an example for a blog post.</p>


Simple AJAX Form

A simple jQuery javascript library to ajax enable forms.

Miguel Useche

<p>This plugin provides a widget and a filter to display a collapsible list of categories in your sidebar or posts by using vanilla Javascript.</p>
<h4>Features</h4>
<ol>
<li>Support for Gutenberg blocks. Add it to any FSE theme or Gutenberg compatible theme.</li>
<li>Display a collapsed list of your archives to reduce space.</li>
<li>Uses vanilla JS to add effects and to be compatible with all browsers.</li>
<li>Select the symbol for expanding/collapsing categories</li>
<li>Select categories to exclude, so it shows only the categories you want.</li>
<li>Autoexpand selected category (including it parent or child).</li>
<li>Support for multiple instances.</li>
<li>Simple layout configuration</li>
<li>Shortcode support  <em>[JsCategoriesList]</em></li>
<li>Translated to Spanish, Italian Russian, Slovak, Czech.</li>
<li>Compatible with most JS cache and minify plugins.</li>
<li>And more to come…</li>
</ol>
<h3>Configuration</h3>
<ul>
<li>Title: title of the widget.</li>
<li>Trigger Symbol:  characters to be displayed as a bullet.</li>
<li>Symbol position: where to put the expand/collapse symbol.</li>
<li>Effect: JS’s effect to use.</li>
<li>Order by: display order of categories.</li>
<li>Expand: if list should be expanded or callapsed by default.</li>
<li>Show number of posts: display how many post are published in the category.</li>
<li>Show empty categories: display categories with no posts.</li>
<li>Categories to include: categories to be included from the list.</li>
<li>Categories to exclude: categories to be excluded from the list.</li>
</ul>


JS Categories List Widget

Haven't seen any problems running this with WordPress 4.9.8, even though it's marked as untested for a long time.  It must have been well written.

Works well with 4.9.8

A simple Gutenberg block and JS widget (can be called from posts) for displaying categories in a list with some effects.

Simple AJAX Form vs JS Categories List Widget