remark-footnotes

npm install remark-footnotes

Here is a footnote reference,[^1]
another,[^longnote],
and optionally there are inline
notes.^[you can type them inline, which may be easier, since you don’t
have to pick an identifier and move down to type the note.]

[^1]: Here is the footnote.

[^longnote]: Here’s one with multiple blocks.

    Subsequent paragraphs are indented to show that they
belong to the previous footnote.

        { some.code }

    The whole paragraph can be indented, or just the first
    line.  In this way, multi-paragraph footnotes work like
    multi-paragraph list items.

This paragraph won’t be part of the note, because it
isn’t indented.

var vfile = require('to-vfile')
var unified = require('unified')
var markdown = require('remark-parse')
var remark2rehype = require('remark-rehype')
var format = require('rehype-format')
var html = require('rehype-stringify')
var footnotes = require('remark-footnotes')

unified()
  .use(markdown)
  .use(footnotes, {inlineNotes: true})
  .use(remark2rehype)
  .use(format)
  .use(html)
  .process(vfile.readSync('example.md'), function (err, file) {
    if (err) throw err
    console.log(String(file))
  })

<p>
  Here is a footnote reference,<sup id="fnref-1"><a href="#fn-1" class="footnote-ref">1</a></sup>
  another,<sup id="fnref-longnote"><a href="#fn-longnote" class="footnote-ref">longnote</a></sup>,
  and optionally there are inline
  notes.<sup id="fnref-2"><a href="#fn-2" class="footnote-ref">2</a></sup>
</p>
<p>
  This paragraph won’t be part of the note, because it
  isn’t indented.
</p>
<div class="footnotes">
  <hr>
  <ol>
    <li id="fn-1">
      <p>Here is the footnote.<a href="#fnref-1" class="footnote-backref">↩</a></p>
    </li>
    <li id="fn-longnote">
      <p>Here’s one with multiple blocks.</p>
      <p>
        Subsequent paragraphs are indented to show that they
        belong to the previous footnote.
      </p>
      <pre><code>{ some.code }
</code></pre>
      <p>
        The whole paragraph can be indented, or just the first
        line. In this way, multi-paragraph footnotes work like
        multi-paragraph list items.<a href="#fnref-longnote" class="footnote-backref">↩</a>
      </p>
    </li>
    <li id="fn-2">
      <p>
        you can type them inline, which may be easier, since you don’t
        have to pick an identifier and move down to type the note.<a href="#fnref-2" class="footnote-backref">↩</a>
      </p>
    </li>
  </ol>
</div>