rehype-remark
rehype plugin that turns HTML into markdown to support remark.
Contents
- What is this?
- When should I use this?
- Install
- Use
- API
- Examples
- Types
- Compatibility
- Security
- Related
- Contribute
- License
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 markdown 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 12.20+, 14.14+, or 16.0+), install with npm:
npm install rehype-remark
In Deno with esm.sh:
import rehypeRemark from 'https://esm.sh/rehype-remark@9'
In browsers with esm.sh:
<script type="module">
import rehypeRemark from 'https://esm.sh/rehype-remark@9?bundle'
</script>
Use
Say we have the following module example.js:
import fetch from 'node-fetch'
import {unified} from 'unified'
import rehypeParse from 'rehype-parse'
import rehypeRemark from 'rehype-remark'
import remarkStringify from 'remark-stringify'
main()
async function main() {
const response = await fetch('https://example.com')
const file = await unified()
.use(rehypeParse)
.use(rehypeRemark)
.use(remarkStringify)
.process(await response.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 defaultHandlers, all, and one. The default export is rehypeRemark.
unified().use(rehypeRemark[, destination][, options])
Plugin that turns HTML into markdown to support remark.
destination
If a Unified destination processor is given, that processor runs with a new markdown (mdast) tree (bridge-mode). As the given processor runs with an mdast tree, and remark plugins support mdast, that means remark plugins can be used with the given processor. The mdast tree is discarded in the end.
👉 Note: It’s highly unlikely that you want to do this.
options
Configuration (optional).
options.newlines
Keep line endings when collapsing whitespace (boolean, default: false). The default collapses to a single space.
options.checked
Value to use for a checked checkbox or radio input (string, default: [x]).
options.unchecked
Value to use for an unchecked checkbox or radio input (string, default: [ ]).
options.quotes
List of quotes to use (Array<string>, default: ['"']). Each value can be one or two characters. When two, the first character determines the opening quote and the second the closing quote at that level. When one, both the opening and closing quote are that character. The order in which the preferred quotes appear determines which quotes to use at which level of nesting. So, to prefer ‘’ at the first level of nesting, and “” at the second, pass ['‘’', '“”']. If <q>s are nested deeper than the given amount of quotes, the markers wrap around: a third level of nesting when using ['«»', '‹›'] should have double guillemets, a fourth single, a fifth double again, etc.
options.document
It’s highly unlikely that you need to change the default of document: true. More info is available in hast-util-to-mdast.
options.handlers
This option is a bit advanced as it requires knowledge of ASTs, so we defer to the documentation available in hast-util-to-mdast.
defaultHandlers
The defaultHandlers export from hast-util-to-mdast, useful when passing in your own handlers.
all
The all export from hast-util-to-mdast, useful when passing in your own handlers.
one
The one export from hast-util-to-mdast, useful when passing in your own handlers.
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:
import {read} from 'to-vfile'
import {unified} from 'unified'
import rehypeParse from 'rehype-parse'
import rehypeRemark from 'rehype-remark'
import remarkStringify from 'remark-stringify'
import {toHtml} from 'hast-util-to-html'
main()
async function main() {
const file = await unified()
.use(rehypeParse, {fragment: true})
.use(rehypeRemark, {
handlers: {
svg(h, node) {
return h(node, 'html', toHtml(node))
}
}
})
.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 Options and Processor types, which specify the interfaces of the accepted parameters. The Handle, H, and Context exports from hast-util-to-mdast are also exported.
Compatibility
Projects maintained by the unified collective are compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, and 16.0+. Our projects sometimes work with older versions, but this is not guaranteed.
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
remark-rehype— remark plugin to turn markdown into HTMLremark-retext— remark plugin to support retextrehype-retext— rehype plugin to support retext
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.