hast-util-to-html
hast utility to serialize hast as HTML.
Contents
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 serializeoptions (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).
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.
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.
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