hast-util-to-html

What is hast-util-to-html?

The hast-util-to-html package is a utility for converting HAST (Hypertext Abstract Syntax Tree) syntax trees to HTML strings. This is particularly useful in the context of unified.js ecosystem for processing HTML content, enabling developers to easily transform markdown or other formats into HTML after processing them through various plugins.

What are hast-util-to-html's main functionalities?

Convert HAST to HTML

This feature allows you to convert a HAST tree to an HTML string. The code sample demonstrates converting a simple paragraph element with text content into its HTML string representation.

const toHtml = require('hast-util-to-html');
const hast = {
  type: 'element',
  tagName: 'p',
  properties: {},
  children: [{type: 'text', value: 'Hello, world!'}]
};
console.log(toHtml(hast));

Other packages similar to hast-util-to-html

rehype-stringify

Part of the rehype ecosystem, which is built on top of unified, rehype-stringify converts HAST to HTML. It is similar to hast-util-to-html but is typically used as a rehype plugin, offering a more integrated experience within the rehype ecosystem.

remark-html

While not directly converting HAST to HTML, remark-html is a plugin for remark (a markdown processor) that allows markdown to be converted to HTML. It serves a similar end goal of transforming content into HTML, but it starts with markdown instead of HAST.

README

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])
  • CharacterReferences
  • Options
  • Quote
  • Space
• 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 (such as formatters) or ugly (such as 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 16+), install with npm:

npm install hast-util-to-html

In Deno with esm.sh:

import {toHtml} from "https://esm.sh/hast-util-to-html@9"

In browsers with esm.sh:

<script type="module">
  import {toHtml} from "https://esm.sh/hast-util-to-html@9?bundle"
</script>

Use

Show install command for this example

npm install hastscript hast-util-to-html

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

const 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 as HTML.

Parameters

• tree (Node or Array<Node>) — tree to serialize
• options (Options, optional) — configuration

Returns

Serialized HTML (string).

CharacterReferences

How to serialize character references (TypeScript type).

Fields

useNamedReferences

Prefer named character references (&) where possible (boolean, default: false).

omitOptionalSemicolons

Whether to omit semicolons when possible (boolean, default: false).

⚠️ Note: this 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.

useShortestReferences

Prefer the shortest possible reference, if that results in less bytes (boolean, default: false).

⚠️ Note: useNamedReferences can be omitted when using useShortestReferences.

Options

Configuration (TypeScript type).

Fields

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.

allowDangerousHtml

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

When false, Raw nodes are encoded.

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

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).

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).

characterReferences

Configure how to serialize character references (CharacterReferences, optional).

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.

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.

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.

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.

preferUnquoted

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

Not used in the SVG space.

quote

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

quoteSmart

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

space

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

When an <svg> element is found in the HTML space, this package 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.

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).

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).

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).

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.

upperDoctype

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

Useless except for XHTML.

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.

Quote

HTML quotes for attribute values (TypeScript type).

Type

type Quote = '"' | "'"

Space

Namespace (TypeScript type).

Type

type Space = 'html' | 'svg'

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 types CharacterReferences, Options, Quote, and Space.

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, hast-util-to-html@^9, compatible with Node.js 16.

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