Awesome
hast-util-to-mdast
hast utility to transform to mdast.
Contents
- What is this?
- When should I use this?
- Install
- Use
- API
- Examples
- Algorithm
- Syntax
- Syntax tree
- Types
- Compatibility
- Security
- Related
- Contribute
- License
What is this?
This package is a utility that takes a hast (HTML) syntax tree as input and turns it into an mdast (markdown) syntax tree.
When should I use this?
This project is useful when you want to turn HTML to markdown.
The mdast utility mdast-util-to-hast
does the inverse of
this utility.
It turns markdown into HTML.
The rehype plugin rehype-remark
wraps this utility to also
turn HTML to markdown 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-mdast
In Deno with esm.sh
:
import {toMdast} from 'https://esm.sh/hast-util-to-mdast@10'
In browsers with esm.sh
:
<script type="module">
import {toMdast} from 'https://esm.sh/hast-util-to-mdast@10?bundle'
</script>
Use
Say we have the following example.html
:
<h2>Hello <strong>world!</strong></h2>
…and next to it a module example.js
:
import fs from 'node:fs/promises'
import {fromHtml} from 'hast-util-from-html'
import {toMdast} from 'hast-util-to-mdast'
import {toMarkdown} from 'mdast-util-to-markdown'
const html = String(await fs.readFile('example.html'))
const hast = fromHtml(html, {fragment: true})
const mdast = toMdast(hast)
const markdown = toMarkdown(mdast)
console.log(markdown)
…now running node example.js
yields:
## Hello **world!**
API
This package exports the identifiers defaultHandlers
,
defaultNodeHandlers
, and
toMdast
.
There is no default export.
toMdast(tree[, options])
Transform hast to mdast.
Parameters
Returns
mdast tree (MdastNode
).
defaultHandlers
Default handlers for elements (Record<string, Handle>
).
Each key is an element name, each value is a Handle
.
defaultNodeHandlers
Default handlers for nodes (Record<string, NodeHandle>
).
Each key is a node type, each value is a NodeHandle
.
Handle
Handle a particular element (TypeScript type).
Parameters
state
(State
) — info passed around about the current stateelement
(Element
) — element to transformparent
(HastParent
) — parent ofelement
Returns
mdast node or nodes (Array<MdastNode> | MdastNode | undefined
).
NodeHandle
Handle a particular node (TypeScript type).
Parameters
state
(State
) — info passed around about the current statenode
(any
) — node to transformparent
(HastParent
) — parent ofnode
Returns
mdast node or nodes (Array<MdastNode> | MdastNode | undefined
).
Options
Configuration (TypeScript type).
Fields
newlines
Keep line endings when collapsing whitespace (boolean
, default: false
).
The default collapses to a single space.
checked
Value to use for a checked checkbox or radio input (string
, default: [x]
).
unchecked
Value to use for an unchecked checkbox or radio input (string
, default:
[ ]
).
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.
document
Whether the given tree represents a complete document (boolean
, default:
undefined
).
Applies when the tree
is a root
node.
When the tree represents a complete document, then things are wrapped in
paragraphs when needed, and otherwise they’re left as-is.
The default checks for whether there’s mixed content: some phrasing nodes
and some non-phrasing nodes.
handlers
Object mapping tag names to functions handling the corresponding elements
(Record<string, Handle>
).
Merged into the defaults.
See Handle
.
nodeHandlers
Object mapping node types to functions handling the corresponding nodes
(Record<string, NodeHandle>
).
Merged into the defaults.
See NodeHandle
.
State
Info passed around about the current state (TypeScript type).
Fields
patch
((from: HastNode, to: MdastNode) => undefined
) — copy a node’s positional infoone
((node: HastNode, parent: HastParent | undefined) => Array<MdastNode> | MdastNode | undefined
) — transform a hast node to mdastall
((parent: HastParent) => Array<MdastContent>
) — transform the children of a hast parent to mdasttoFlow
((nodes: Array<MdastContent>) => Array<MdastFlowContent>
) — transform a list of mdast nodes to flowtoSpecificContent
(<ParentType>(nodes: Array<MdastContent>, build: (() => ParentType)) => Array<ParentType>
) — turn arbitrary content into a list of a particular node typeresolve
((url: string | null | undefined) => string
) — resolve a URL relative to a baseoptions
(Options
) — user configurationelementById
(Map<string, Element>
) — elements by theirid
handlers
(Record<string, Handle>
) — applied element handlers (seeHandle
)nodeHandlers
(Record<string, NodeHandle>
) — applied node handlers (seeNodeHandle
)baseFound
(boolean
) — whether a<base>
element was seenfrozenBaseUrl
(string | undefined
) —href
of<base>
, if anyinTable
(boolean
) — whether we’re in a tableqNesting
(number
) — how deep we’re in<q>
s
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>Strong</strong> and <em data-mdast="ignore">emphasis</em>.</p>
Yields:
**Strong** and .
It’s also possible to pass a handler to ignore nodes.
For example, to ignore em
elements, pass handlers: {'em': function () {}}
:
<p><strong>Strong</strong> and <em>emphasis</em>.</p>
Yields:
**Strong** and .
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>
This can be achieved with example.js
like so:
/**
* @typedef {import('mdast').Html} Html
*/
import fs from 'node:fs/promises'
import {fromHtml} from 'hast-util-from-html'
import {toHtml} from 'hast-util-to-html'
import {toMdast} from 'hast-util-to-mdast'
import {toMarkdown} from 'mdast-util-to-markdown'
const html = String(await fs.readFile('example.html'))
const hast = fromHtml(html, {fragment: true})
const mdast = toMdast(hast, {
handlers: {
svg(state, node) {
/** @type {Html} */
const result = {type: 'html', value: toHtml(node, {space: 'svg'})}
state.patch(node, result)
return result
}
}
})
const markdown = toMarkdown(mdast)
console.log(markdown)
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?
<!-- Old ID of this section. -->
<a name="implied-paragraphs"></a>
Algorithm
The algorithm used in this project is very powerful.
It supports all HTML elements, including ancient elements (xmp
) and obscure
ones (base
).
It’s particularly good at forms, media, and around implicit and explicit
paragraphs (see HTML Standard, A. van Kesteren; et al. WHATWG § 3.2.5.4
Paragraphs), such as:
<article>
An implicit paragraph.
<h1>An explicit paragraph.</h1>
</article>
Yields:
An implicit paragraph.
# An explicit paragraph.
Syntax
HTML is handled according to WHATWG HTML (the living standard), which is also followed by browsers such as Chrome and Firefox.
This project creates markdown according to GFM, which is a standard that’s
based on CommonMark but adds the strikethrough (~like so~
) and tables
(| Table header | …
) amongst some alternative syntaxes.
Syntax tree
The input syntax tree format is hast. Any HTML that can be represented in hast is accepted as input. The output syntax tree format is mdast.
When <table>
elements or <del>
, <s>
, and <strike>
exist in the HTML,
then the GFM nodes table
and delete
are used.
This utility does not generate definitions or references, or syntax extensions
such as footnotes, frontmatter, or math.
Types
This package is fully typed with TypeScript.
It exports the additional types Handle
,
NodeHandle
,
Options
,
and State
.
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-mdast@^10
,
compatible with Node.js 16.
Security
Use of hast-util-to-mdast
is safe by default.
Related
hast-util-to-nlcst
— transform hast to nlcsthast-util-to-xast
— transform hast to xast
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.