micromark extension to support GitHub flavored markdown (GFM) footnotes.

• What is this?
• When to use this
• Install
• Use
• API
  • gfmFootnote()
  • gfmFootnoteHtml(htmlOptions)
• Recommended CSS
• Types
• Compatibility
• Security
• Related
• Contribute
• License

This package is a micromark extension to add support for GFM footnotes. GFM footnotes were announced September 30, 2021 but are not yet specified. Their implementation on github.com is currently quite buggy. The bugs have been reported on cmark-gfm. This micromark extension matches github.com except for its bugs.

In many cases, when working with micromark, you’d want to use micromark-extension-gfm instead, which combines this package with other GFM features.

When working with syntax trees, you’d want to combine this package with mdast-util-gfm-footnote (or mdast-util-gfm when using micromark-extension-gfm).

These tools are all rather low-level. In most cases, you’d instead want to use remark-gfm with remark.

This package is ESM only. In Node.js (version 12.20+, 14.14+, or 16.0+), install with npm:

npm install micromark-extension-gfm-footnote

In Deno with Skypack:

import {gfmFootnote, gfmFootnoteHtml} from 'https://cdn.skypack.dev/micromark-extension-gfm-footnote@1?dts'

In browsers with Skypack:

<script type="module">
  import {gfmFootnote, gfmFootnoteHtml} from 'https://cdn.skypack.dev/micromark-extension-gfm-footnote@1?min'
</script>

Say we have the following file example.md:

Using footnotes is fun![^1] They let you reference relevant information without disrupting the flow of what you’re trying to say.[^bignote]

[^1]: This is the first footnote.
[^bignote]: Here’s one with multiple paragraphs and code.

    Indent paragraphs to include them in the footnote.

    ```
    my code
    ```

    Add as many paragraphs as you like.

Text here and here and here.
[Learn more about markdown and footnotes in markdown](https://docs.github.com/en/github/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#footnotes)

And our module example.js looks as follows:

import fs from 'node:fs'
import {micromark} from 'micromark'
import {gfmFootnote, gfmFootnoteHtml} from 'micromark-extension-gfm-footnote'

const output = micromark(fs.readFileSync('example.md'), {
  extensions: [gfmFootnote()],
  htmlExtensions: [gfmFootnoteHtml()]
})

console.log(output)

Now running node example.js yields:

<p>Using footnotes is fun!<sup><a href="#user-content-fn-1" id="user-content-fnref-1" data-footnote-ref="" aria-describedby="footnote-label">1</a></sup> They let you reference relevant information without disrupting the flow of what you’re trying to say.<sup><a href="#user-content-fn-bignote" id="user-content-fnref-bignote" data-footnote-ref="" aria-describedby="footnote-label">2</a></sup></p>
<p>Text here and here and here.
<a href="https://docs.github.com/en/github/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#footnotes">Learn more about markdown and footnotes in markdown</a></p>
<section data-footnotes="" class="footnotes"><h2 id="footnote-label" class="sr-only">Footnotes</h2>
<ol>
<li id="user-content-fn-1">
<p>This is the first footnote. <a href="#user-content-fnref-1" data-footnote-backref="" class="data-footnote-backref" aria-label="Back to content">↩</a></p>
</li>
<li id="user-content-fn-bignote">
<p>Here’s one with multiple paragraphs and code.</p>
<p>Indent paragraphs to include them in the footnote.</p>
<pre><code>my code
</code></pre>
<p>Add as many paragraphs as you like. <a href="#user-content-fnref-bignote" data-footnote-backref="" class="data-footnote-backref" aria-label="Back to content">↩</a></p>
</li>
</ol>
</section>

This package exports the following identifiers: gfmFootnote, gfmFootnoteHtml. There is no default export.

The export map supports the endorsed development condition. Run node --conditions development module.js to get instrumented dev code. Without this condition, production code is loaded.

A function that can be called to get an extension for micromark to parse GFM footnotes (can be passed in extensions).

A function that can be called to get an extension to compile them to HTML (can be passed in htmlExtensions).

Prefix to use before the id attribute to prevent it from clobbering attributes (string, default: 'user-content-'). DOM clobbering is this:

<p id=x></p>
<script>alert(x)</script>

Elements by their ID are made available in browsers on the window object. Using a prefix this that from being a problem.

Label to use for the footnotes section (string, default: 'Footnotes'). Affects screen reader users. Change it if you’re authoring in a different language.

Label to use from backreferences back to their footnote call (string, default: 'Back to content'). Affects screen reader users. Change it if you’re authoring in a different language.

The following CSS is needed to make footnotes look a bit like GitHub. For the complete actual CSS see sindresorhus/github-markdown-css.

/* Style the footnotes section. */
.footnotes {
  font-size: smaller;
  color: #8b949e;
  border-top: 1px solid #30363d;
}

/* Hide the section label for visual users. */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  word-wrap: normal;
  border: 0;
}

/* Place `[` and `]` around footnote calls. */
[data-footnote-ref]::before {
  content: '[';
}

[data-footnote-ref]::after {
  content: ']';
}

This package is fully typed with TypeScript. It exports additional HtmlOptions type that models its respective interface.

This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, and 16.0+. It also works in Deno and modern browsers.

This package is safe.

• syntax-tree/mdast-util-gfm-footnote — support GFM footnotes in mdast
• syntax-tree/mdast-util-gfm — support GFM in mdast
• remarkjs/remark-gfm — support GFM in remark

See contributing.md in micromark/.github for ways to get started. See support.md for ways to get help.

This project has a code of conduct. By interacting with this repository, organization, or community you agree to abide by its terms.

MIT © Titus Wormer