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rehype plugin that turns HTML into markdown to support remark.

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What is this?

This package is a unified (rehype) plugin that switches from rehype (the HTML ecosystem) to remark (the markdown ecosystem). It does this by transforming the current HTML (hast) syntax tree into a markdown (mdast) syntax tree. rehype plugins deal with hast and remark plugins deal with mdast, so plugins used after rehype-remark have to be remark plugins.

The reason that there are different ecosystems for markdown and HTML is that turning markdown into HTML is, while frequently needed, not the only purpose of markdown. Checking (linting) and formatting markdown are also common use cases for remark and markdown. There are several aspects of markdown that do not translate 1-to-1 to HTML. In some cases markdown contains more information than HTML: for example, there are several ways to add a link in markdown (as in, autolinks: <https://url>, resource links: [label](url), and reference links with definitions: [label][id] and [id]: url). In other cases HTML contains more information than markdown: there are many tags, which add new meaning (semantics), available in HTML that aren’t available in markdown. If there was just one AST, it would be quite hard to perform the tasks that several remark and rehype plugins currently do.

unified is a project that transforms content with abstract syntax trees (ASTs). remark adds support for markdown to unified. rehype adds support for HTML to unified. mdast is the markdown AST that remark uses. hast is the HTML AST that rehype uses. This is a rehype plugin that transforms hast into mdast to support remark.

When should I use this?

This project is useful when you want to turn HTML to markdown.

The remark plugin remark-rehype does the inverse of this plugin. It turns markdown into HTML.

Install

This package is ESM only. In Node.js (version 16+), install with npm:

npm install rehype-remark

In Deno with esm.sh:

import rehypeRemark from 'https://esm.sh/rehype-remark@10'

In browsers with esm.sh:

<script type="module">
  import rehypeRemark from 'https://esm.sh/rehype-remark@10?bundle'
</script>

Use

Say we have the following module example.js:

import rehypeParse from 'rehype-parse'
import rehypeRemark from 'rehype-remark'
import remarkStringify from 'remark-stringify'
import {fetch} from 'undici'
import {unified} from 'unified'

const response = await fetch('https://example.com')
const text = await response.text()

const file = await unified()
  .use(rehypeParse)
  .use(rehypeRemark)
  .use(remarkStringify)
  .process(text)

console.log(String(file))

Now running node example.js yields:

# Example Domain

This domain is for use in illustrative examples in documents. You may use this domain in literature without prior coordination or asking for permission.

[More information...](https://www.iana.org/domains/example)

API

This package exports no identifiers. The default export is rehypeRemark.

unified().use(rehypeRemark[, destination][, options])

Turn HTML into markdown.

Parameters
Returns

Transform (Transformer).

Notes

👉 Note: It’s highly unlikely that you want to pass a processor.

Options

Configuration (TypeScript type).

Fields

Examples

Example: ignoring things

It’s possible to exclude something from within HTML when turning it into markdown, by wrapping it in an element with a data-mdast attribute set to 'ignore'. For example:

<p><strong>Importance</strong> and <em data-mdast="ignore">emphasis</em>.</p>

Yields:

**Importance** and .

It’s also possible to pass a handler to ignore nodes, or create your own plugin that uses more advanced filters.

Example: keeping some HTML

The goal of this project is to map HTML to plain and readable markdown. That means that certain elements are ignored (such as <svg>) or “downgraded” (such as <video> to links). You can change this by passing handlers.

Say we have the following file example.html:

<p>
  Some text with
  <svg viewBox="0 0 1 1" width="1" height="1"><rect fill="black" x="0" y="0" width="1" height="1" /></svg>
  a graphic… Wait is that a dead pixel?
</p>

And our module example.js looks as follows:

/**
 * @typedef {import('mdast').Html} Html
 */

import {toHtml} from 'hast-util-to-html'
import rehypeParse from 'rehype-parse'
import rehypeRemark from 'rehype-remark'
import remarkStringify from 'remark-stringify'
import {read} from 'to-vfile'
import {unified} from 'unified'

const file = await unified()
  .use(rehypeParse, {fragment: true})
  .use(rehypeRemark, {
    handlers: {
      svg(state, node) {
        /** @type {Html} */
        const result = {type: 'html', value: toHtml(node)}
        state.patch(node, result)
        return result
      }
    }
  })
  .use(remarkStringify)
  .process(await read('example.html'))

console.log(String(file))

Now running node example.js yields:

Some text with <svg viewBox="0 0 1 1" width="1" height="1"><rect fill="black" x="0" y="0" width="1" height="1"></rect></svg> a graphic… Wait is that a dead pixel?

Types

This package is fully typed with TypeScript. It exports the additional type Options. More advanced types are exposed from hast-util-to-mdast.

Compatibility

Projects maintained by the unified collective are compatible with maintained versions of Node.js.

When we cut a new major release, we drop support for unmaintained versions of Node. This means we try to keep the current release line, rehype-remark@^10, compatible with Node.js 16.

This plugin works with unified version 6+, rehype-parse version 3+ (used in rehype version 5), and remark-stringify version 3+ (used in remark version 7).

Security

Use of rehype-remark is safe by default.

Related

Contribute

See contributing.md in rehypejs/.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.

License

MIT © Titus Wormer

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