hast-util-to-html

hast utility to serialize hast as HTML.

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • toHtml(tree[, options])
• Syntax
• Types
• Compatibility
• Security
• Related
• Contribute
• License

What is this?

This package is a utility that turns a hast tree into a string of HTML.

When should I use this?

You can use this utility when you want to get the serialized HTML that is represented by the syntax tree, either because you’re done with the syntax tree, or because you’re integrating with another tool that does not support syntax trees.

This utility has many options to configure how the HTML is serialized. These options help when building tools that make output pretty (e.g., formatters) or ugly (e.g., minifiers).

The utility hast-util-from-html does the inverse of this utility. It turns HTML into hast.

The rehype plugin rehype-stringify wraps this utility to also serialize HTML at a higher-level (easier) abstraction.

Install

This package is ESM only. In Node.js (version 12.20+, 14.14+, 16.0+, or 18.0+), install with npm:

npm install hast-util-to-html

In Deno with esm.sh:

import {toHtml} from "https://esm.sh/hast-util-to-html@8"

In browsers with esm.sh:

<script type="module">
  import {toHtml} from "https://esm.sh/hast-util-to-html@8?bundle"
</script>

Use

npm install hastscript hast-util-to-html

import {h} from 'hastscript'
import {toHtml} from 'hast-util-to-html'

var tree = h('.alpha', [
  'bravo ',
  h('b', 'charlie'),
  ' delta ',
  h('a.echo', {download: true}, 'foxtrot')
])

console.log(toHtml(tree))

Yields:

<div class="alpha">bravo <b>charlie</b> delta <a class="echo" download>foxtrot</a></div>

API

This package exports the identifier toHtml. There is no default export.

toHtml(tree[, options])

Serialize hast (Node, Array<Node>) as HTML.

options

Configuration (optional).

options.entities

Define how to create character references (Object, default: {}). Configuration is passed to stringify-entities. You can use the fields useNamedReferences, useShortestReferences, and omitOptionalSemicolons. You cannot use the fields escapeOnly, attribute, or subset).

options.upperDoctype

Use a <!DOCTYPE… instead of <!doctype…. Useless except for XHTML (boolean, default: false).

options.quote

Preferred quote to use ('"' or '\'', default: '"').

options.quoteSmart

Use the other quote if that results in less bytes (boolean, default: false).

options.preferUnquoted

Leave attributes unquoted if that results in less bytes (boolean, default: false).

Not used in the SVG space.

options.omitOptionalTags

Omit optional opening and closing tags (boolean, default: false). For example, 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.

options.collapseEmptyAttributes

Collapse empty attributes: get class instead of class="" (boolean, default: false).

Not used in the SVG space.

👉 Note: boolean attributes (such as hidden) are always collapsed.

options.closeSelfClosing

Close self-closing nodes with an extra slash (/): <img /> instead of <img> (boolean, default: false). See tightSelfClosing to control whether a space is used before the slash.

Not used in the SVG space.

options.closeEmptyElements

Close SVG elements without any content with slash (/) on the opening tag instead of an end tag: <circle /> instead of <circle></circle> (boolean, default: false). See tightSelfClosing to control whether a space is used before the slash.

Not used in the HTML space.

options.tightSelfClosing

Do not use an extra space when closing self-closing elements: <img/> instead of <img /> (boolean, default: false).

👉 Note: only used if closeSelfClosing: true or closeEmptyElements: true.

options.tightCommaSeparatedLists

Join known comma-separated attribute values with just a comma (,), instead of padding them on the right as well (,␠, where ␠ represents a space) (boolean, default: false).

options.tightAttributes

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 (boolean, default: false).

Not used in the SVG space.

👉 Note: intentionally creates parse errors in markup (how parse errors are handled is well defined, so this works but isn’t pretty).

options.tightDoctype

Drop unneeded spaces in doctypes: <!doctypehtml> instead of <!doctype html> to save bytes (boolean, default: false).

👉 Note: intentionally creates parse errors in markup (how parse errors are handled is well defined, so this works but isn’t pretty).

options.bogusComments

Use “bogus comments” instead of comments to save byes: <?charlie> instead of <!--charlie--> (boolean, default: false).

👉 Note: intentionally creates parse errors in markup (how parse errors are handled is well defined, so this works but isn’t pretty).

options.allowParseErrors

Do not encode characters which cause parse errors (even though they work), to save bytes (boolean, default: false).

Not used in the SVG space.

👉 Note: intentionally creates parse errors in markup (how parse errors are handled is well defined, so this works but isn’t pretty).

options.allowDangerousCharacters

Do not encode some characters which cause XSS vulnerabilities in older browsers (boolean, default: false).

⚠️ Danger: only set this if you completely trust the content.

options.allowDangerousHtml

Allow raw nodes and insert them as raw HTML. When falsey, encodes raw nodes (boolean, default: false).

⚠️ Danger: only set this if you completely trust the content.

options.space

Which space the document is in ('svg' or 'html', default: 'html').

When an <svg> element is found in the HTML space, rehype-stringify already automatically switches to and from the SVG space when entering and exiting it.

👉 Note: hast is not XML. It supports SVG as embedded in HTML. It does not support the features available in XML. Passing SVG might break but fragments of modern SVG should be fine. Use xast if you need to support SVG as XML.

options.voids

Tag names of elements to serialize without closing tag (Array<string>, default: html-void-elements).

Not used in the SVG space.

👉 Note: It’s highly unlikely that you want to pass this, because hast is not for XML, and HTML will not add more void elements.

Returns

Serialized HTML (string).

Syntax

HTML is serialized according to WHATWG HTML (the living standard), which is also followed by browsers such as Chrome and Firefox.

Types

This package is fully typed with TypeScript. It exports the additional type Options.

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.

Security

Use of hast-util-to-html can open you up to a cross-site scripting (XSS) attack if the hast tree is unsafe. Use hast-util-santize to make the hast tree safe.

Related

• hast-util-sanitize — sanitize hast

Contribute

See contributing.md in syntax-tree/.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