This Eleventy plugin will generate a TOC from page content using an Eleventy filter.

{
  tags: ['h2', 'h3', 'h4'], // which heading tags are selected
                            // headings must each have an ID attribute
  wrapper: 'nav',           // element to put around the root `ol`
  wrapperClass: 'toc'       // class for the element around the root `ol`
}

npm i --save eleventy-plugin-toc

Note: you'll need to make sure you have ids on heading elements before this plugin will create a TOC. If there aren't ids, there will be nothing for links in this TOC to link to. (I recommend using markdown-it-anchor to add those ids to the headings: Eleventy config example)

// .eleventy.js

const pluginTOC = require('eleventy-plugin-toc')

module.exports = function (eleventyConfig) {
  eleventyConfig.addPlugin(pluginTOC)
}

<article>
  {{ content }}
</article>
<aside>
  {{ content | toc }}
</article>

Pass a stringified JSON object (must be JSON.parse()-able) as an option for in your template. Because this is an object, you only need to include the key-value pairs you need to override; defaults will be preserved.

<aside>
  {{ content | toc: '{"tags":["h2","h3"],"wrapper":"div","wrapperClass":"content-tableau"}' }}
</article>

• I'd like to expose the default options to overriding in an Eleventy config file
• Some tests would be nice