rehype-stringify

rehype plugin to add support for serializing to HTML.

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • unified().use(rehypeStringify[, options])
  • CharacterReferences
  • Options
• Syntax
• Syntax tree
• Types
• Compatibility
• Security
• Contribute
• Sponsor
• License

What is this?

This package is a unified (rehype) plugin that defines how to take a syntax tree as input and turn it into serialized HTML. When it’s used, HTML is serialized as the final result.

See the monorepo readme for info on what the rehype ecosystem is.

When should I use this?

This plugin adds support to unified for serializing HTML. If you also need to parse HTML, you can alternatively use rehype, which combines unified, rehype-parse, and this plugin.

When you are in a browser, trust your content, don’t need formatting options, and value a smaller bundle size, you can use rehype-dom-stringify instead.

If you don’t use plugins and have access to a syntax tree, you can directly use hast-util-to-html, which is used inside this plugin. rehype focusses on making it easier to transform content by abstracting such internals away.

A different plugin, rehype-format, improves the readability of HTML source code as it adds insignificant but pretty whitespace between elements. There is also the preset rehype-minify for when you want the inverse: minified and mangled HTML.

Install

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

npm install rehype-stringify

In Deno with esm.sh:

import rehypeStringify from 'https://esm.sh/rehype-stringify@10'

In browsers with esm.sh:

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

Use

Say we have the following module example.js:

import remarkRehype from 'remark-rehype'
import rehypeStringify from 'rehype-stringify'
import remarkGfm from 'remark-gfm'
import remarkParse from 'remark-parse'
import {unified} from 'unified'

const file = await unified()
  .use(remarkParse)
  .use(remarkGfm)
  .use(remarkRehype)
  .use(rehypeStringify)
  .process('# Hi\n\n*Hello*, world!')

console.log(String(file))

…running that with node example.js yields:

<h1>Hi</h1>
<p><em>Hello</em>, world!</p>

API

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

unified().use(rehypeStringify[, options])

Plugin to add support for serializing to HTML.

Parameters

• options (Options, optional) — configuration

Returns

Nothing (undefined).

CharacterReferences

How to serialize character references (TypeScript type).

⚠️ Note: omitOptionalSemicolons creates what HTML calls “parse errors” but is otherwise still valid HTML — don’t use this except when building a minifier. Omitting semicolons is possible for certain named and numeric references in some cases.

⚠️ Note: useNamedReferences can be omitted when using useShortestReferences.

Fields

• useNamedReferences (boolean, default: false) — prefer named character references (&) where possible
• omitOptionalSemicolons (boolean, default: false) — whether to omit semicolons when possible
• useShortestReferences (boolean, default: false) — prefer the shortest possible reference, if that results in less bytes

Options

Configuration (TypeScript type).

⚠️ Danger: only set allowDangerousCharacters and allowDangerousHtml if you completely trust the content.

👉 Note: allowParseErrors, bogusComments, tightAttributes, and tightDoctype intentionally create parse errors in markup (how parse errors are handled is well defined, so this works but isn’t pretty).

👉 Note: this is not an XML serializer. It supports SVG as embedded in HTML. It does not support the features available in XML. Use xast-util-to-xml to serialize XML.

Fields

• allowDangerousCharacters (boolean, default: false) — do not encode some characters which cause XSS vulnerabilities in older browsers
• allowDangerousHtml (boolean, default: false) — allow Raw nodes and insert them as raw HTML; when false, Raw nodes are encoded
• allowParseErrors (boolean, default: false) — do not encode characters which cause parse errors (even though they work), to save bytes; not used in the SVG space.
• bogusComments (boolean, default: false) — use “bogus comments” instead of comments to save byes: <?charlie> instead of <!--charlie-->
• characterReferences (CharacterReferences, optional) — configure how to serialize character references
• closeEmptyElements (boolean, default: false) — close SVG elements without any content with slash (/) on the opening tag instead of an end tag: <circle /> instead of <circle></circle>; see tightSelfClosing to control whether a space is used before the slash; not used in the HTML space
• closeSelfClosing (boolean, default: false) — close self-closing nodes with an extra slash (/): <img /> instead of <img>; see tightSelfClosing to control whether a space is used before the slash; not used in the SVG space.
• collapseEmptyAttributes (boolean, default: false) — collapse empty attributes: get class instead of class=""; not used in the SVG space; boolean attributes (such as hidden) are always collapsed
• omitOptionalTags (boolean, default: false) — omit optional opening and closing tags; to illustrate, in <ol><li>one</li><li>two</li></ol>, both </li> closing tags can be omitted, the first because it’s followed by another li, the last because it’s followed by nothing; not used in the SVG space
• preferUnquoted (boolean, default: false) — leave attributes unquoted if that results in less bytes; not used in the SVG space
• quote ('"' or "'", default: '"') — preferred quote to use
• quoteSmart (boolean, default: false) — use the other quote if that results in less bytes
• space ('html' or 'svg', default: 'html') — which space the document is in; when an <svg> element is found in the HTML space, this package already automatically switches to and from the SVG
• tightAttributes (boolean, default: false) — join attributes together, without whitespace, if possible: get class="a b"title="c d" instead of class="a b" title="c d" to save bytes; not used in the SVG space
• tightCommaSeparatedLists (boolean, default: false) — join known comma-separated attribute values with just a comma (,), instead of padding them on the right as well (,␠, where ␠ represents a space)
• tightDoctype (boolean, default: false) — drop unneeded spaces in doctypes: <!doctypehtml> instead of <!doctype html> to save bytes
• tightSelfClosing (boolean, default: false). — do not use an extra space when closing self-closing elements: <img/> instead of <img />; only used if closeSelfClosing: true or closeEmptyElements: true
• upperDoctype (boolean, default: false). — use a <!DOCTYPE… instead of <!doctype…; useless except for XHTML
• voids (Array<string>, default: html-void-elements) — tag names of elements to serialize without closing tag; not used in the SVG space

Syntax

HTML is serialized according to WHATWG HTML (the living standard), which is also followed by all browsers.

Syntax tree

The syntax tree format used in rehype is hast.

Types

This package is fully typed with TypeScript. It exports the additional types CharacterReferences and Options.

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-stringify@^10, compatible with Node.js 16.

Security

As rehype works on HTML, and improper use of HTML can open you up to a cross-site scripting (XSS) attack, use of rehype can also be unsafe. Use rehype-sanitize to make the tree safe.

Use of rehype plugins could also open you up to other attacks. Carefully assess each plugin and the risks involved in using them.

For info on how to submit a report, see our security policy.

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.

Sponsor

Support this effort and give back by sponsoring on OpenCollective!

License

MIT © Titus Wormer