mdast-util-to-markdown

mdast utility to serialize markdown

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mdast-util-to-markdown
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mdast utility that turns a syntax tree into markdown.

Contents

*   [`toMarkdown(tree[, options])`](#tomarkdowntree-options)
*   [`defaultHandlers`](#defaulthandlers)
*   [`ConstructName`](#constructname)
*   [`ConstructNameMap`](#constructnamemap)
*   [`Handle`](#handle)
*   [`Handlers`](#handlers)
*   [`Info`](#info)
*   [`Join`](#join)
*   [`Map`](#map)
*   [`Options`](#options)
*   [`SafeConfig`](#safeconfig)
*   [`State`](#state)
*   [`Tracker`](#tracker)
*   [`Unsafe`](#unsafe)

What is this?

This package is a utility that takes an mdast
syntax tree as input and turns it into serialized markdown.
This utility is a low level project. It’s used in remark-stringifyremark-stringify, which focusses on making it easier to transform content by abstracting these internals away.

When should I use this?

If you want to handle syntax trees manually, use this. For an easier time processing content, use the remark ecosystem instead.
You can combine this utility with other utilities to add syntax extensions. Notable examples that deeply integrate with it are mdast-util-gfm
mdast-util-gfm, mdast-util-mdxmdast-util-mdx, mdast-util-frontmattermdast-util-frontmatter, mdast-util-mathmdast-util-math, and mdast-util-directivemdast-util-directive.

Install

This package is ESM onlyesm. In Node.js (version 14.14+, or 16.0+), install with npm:
npm install mdast-util-to-markdown

In Deno with esm.shesmsh:
import {toMarkdown} from 'https://esm.sh/mdast-util-to-markdown@1'

In browsers with esm.shesmsh:
<script type="module">
  import {toMarkdown} from 'https://esm.sh/mdast-util-to-markdown@1?bundle'
</script>

Use

Say our module example.js looks as follows:
import {toMarkdown} from 'mdast-util-to-markdown'

/** @type {import('mdast').Root} */
const tree = {
  type: 'root',
  children: [
    {
      type: 'blockquote',
      children: [
        {type: 'thematicBreak'},
        {
          type: 'paragraph',
          children: [
            {type: 'text', value: '- a\nb !'},
            {
              type: 'link',
              url: 'example.com',
              children: [{type: 'text', value: 'd'}]
            }
          ]
        }
      ]
    }
  ]
}

console.log(toMarkdown(tree))

…now running node example.js yields:
> ***
>
> \- a
> b \![d](example.com)

πŸ‘‰ Note: observe the properly escaped characters which would otherwise turn into a list and image respectively.

API

This package exports the identifiers toMarkdown and defaultHandlers. There is no default export.

toMarkdown(tree[, options])

Turn an mdast syntax tree into markdown.
Parameters
β€” tree to serialize
β€” configuration
Returns
Serialized markdown representing tree (string).

defaultHandlers

Default (CommonMark) handlers (Handlers
handlers).

ConstructName

Construct names for things generated by mdast-util-to-markdown (TypeScript type).
This is an enum of strings, each being a semantic label, useful to know when serializing whether we’re for example in a double (") or single (') quoted title.
Type
type ConstructName = ConstructNameMap[keyof ConstructNameMap]

ConstructNameMap

Interface of registered constructs (TypeScript type).
Type
interface ConstructNameMap { /* see code */ }

When working on extensions that use new constructs, extend the corresponding interface to register its name:
declare module 'mdast-util-to-markdown' {
  interface ConstructNameMap {
    // Register a new construct name (value is used, key should match it).
    gfmStrikethrough: 'gfmStrikethrough'
  }
}

Handle

Handle a particular node (TypeScript type).
Parameters
  • node (any)
β€” expected mdast node
β€” parent of `node`
β€” info passed around about the current state
β€” info on the surrounding of the node that is serialized
Returns
Serialized markdown representing node (string).

Handlers

Handle particular nodes (TypeScript type).
Each key is a node type (Node['type']), each value its corresponding handler (Handlehandle).
Type
type Handlers = Record<Node['type'], Handle>

Info

Info on the surrounding of the node that is serialized (TypeScript type).
Fields
β€” current point
  • lineShift (number)
β€” number of columns each line will be shifted by wrapping nodes
  • before (string)
β€” characters before this (guaranteed to be one, can be more)
  • after (string)
β€” characters after this (guaranteed to be one, can be more)

Join

How to join two blocks (TypeScript type).
β€œBlocks” are typically joined by one blank line. Sometimes it’s nicer to have them flush next to each other, yet other times they cannot occur together at all.
Join functions receive two adjacent siblings and their parent and what they return defines how many blank lines to use between them.
Parameters
β€” first of two adjacent siblings
β€” second of two adjacent siblings
β€” parent of the two siblings
β€” info passed around about the current state
Returns
How many blank lines to use between the siblings (boolean, number, optional).
Where true is as passing 1 and false means the nodes cannot be joined by a blank line, such as two adjacent block quotes or indented code after a list, in which case a comment will be injected to break them up:
> Quote 1

<!---->

> Quote 2

πŸ‘‰ Note: abusing this feature will break markdown. One such example is when returning 0 for two paragraphs, which will result in the text running together, and in the future to be seen as one paragraph.

Map

Map function to pad a single line (TypeScript type).
Parameters
  • value (string)
β€” a single line of serialized markdown
  • line (number)
β€” line number relative to the fragment
  • blank (boolean)
β€” whether the line is considered blank in markdown
Returns
Padded line (string).

Options

Configuration (TypeScript type).
Fields
The following fields influence how markdown is serialized.
options.bullet
Marker to use for bullets of items in unordered lists ('*', '+', or '-', default: '*').
options.bulletOther
Marker to use in certain cases where the primary bullet doesn’t work ('*', '+', or '-', default: depends).
There are three cases where the primary bullet cannot be used:
  • When three list items are on their own, the last one is empty, and bullet
is also a valid `rule`: `* - +`.
This would turn into a thematic break if serialized with three primary
bullets.
As this is an edge case unlikely to appear in normal markdown, the last list
item will be given a different bullet.
  • When a thematic break is the first child of one of the list items, and
`bullet` is the same character as `rule`: `- ***`.
This would turn into a single thematic break if serialized with primary
bullets.
As this is an edge case unlikely to appear in normal markdown this markup is
always fixed, even if `bulletOther` is not passed
  • When two unordered lists appear next to each other: * a\n- b.
CommonMark sees different bullets as different lists, but several markdown
parsers parse it as one list.
To solve for both, we instead inject an empty comment between the two lists:
`* a\n<!---->\n* b`, but if `bulletOther` is given explicitly, it will be
used instead
options.bulletOrdered
Marker to use for bullets of items in ordered lists ('.' or ')', default: '.').
options.bulletOrderedOther
Marker to use in certain cases where the primary bullet for ordered items doesn’t work ('.' or ')', default: none).
There is one case where the primary bullet for ordered items cannot be used:
  • When two ordered lists appear next to each other: 1. a\n2) b.
CommonMark added support for `)` as a marker, but other markdown parsers
do not support it.
To solve for both, we instead inject an empty comment between the two lists:
`1. a\n<!---->\n1. b`, but if `bulletOrderedOther` is given explicitly, it
will be used instead
options.closeAtx
Whether to add the same number of number signs (#) at the end of an ATX heading as the opening sequence (boolean, default: false).
options.emphasis
Marker to use for emphasis ('*' or '_', default: '*').
options.fence
Marker to use for fenced code (`''` or '~', default: ''``).
options.fences
Whether to use fenced code always (boolean, default: false). The default is to use fenced code if there is a language defined, if the code is empty, or if it starts or ends in blank lines.
options.incrementListMarker
Whether to increment the counter of ordered lists items (boolean, default: true).
options.listItemIndent
How to indent the content of list items ('one', 'tab', or 'mixed', default: 'tab'). Either with the size of the bullet plus one space (when 'one'), a tab stop ('tab'), or depending on the item and its parent list ('mixed', uses 'one' if the item and list are tight and 'tab' otherwise).
options.quote
Marker to use for titles ('"' or "'", default: '"').
options.resourceLink
Whether to always use resource links (boolean, default: false). The default is to use autolinks (<https://example.com>) when possible and resource links ([text](url)) otherwise.
options.rule
Marker to use for thematic breaks ('*', '-', or '_', default: '*').
options.ruleRepetition
Number of markers to use for thematic breaks (number, default: 3, min: 3).
options.ruleSpaces
Whether to add spaces between markers in thematic breaks (boolean, default: false).
options.setext
Whether to use setext headings when possible (boolean, default: false). The default is to always use ATX headings (# heading) instead of setext headings (heading\n=======). Setext headings cannot be used for empty headings or headings with a rank of three or more.
options.strong
Marker to use for strong ('*' or '_', default: '*').
options.tightDefinitions
Whether to join definitions without a blank line (boolean, default: false).
The default is to add blank lines between any flow (β€œblock”) construct. Turning this option on is a shortcut for a Joinjoin function like so:
function joinTightDefinitions(left, right) {
  if (left.type === 'definition' && right.type === 'definition') {
    return 0
  }
}
options.handlers
Handle particular nodes (Handlershandlers, optional).
options.join
How to join blocks (Array<Join>join, optional).
options.unsafe
Schemas that define when characters cannot occur (Array<Unsafe>unsafe, optional).
options.extensions
List of extensions (Array<Options>, default: []). Each extension is an object with the same interface as Options itself.

SafeConfig

Configuration passed to state.safe (TypeScript type).
Fields
  • before (string)
β€” characters before this (guaranteed to be one, can be more)
  • after (string)
β€” characters after this (guaranteed to be one, can be more)
  • encode (Array<string>, optional)
β€” extra characters that *must* be encoded (as character references) instead
of escaped (character escapes).
Only ASCII punctuation will use character escapes, so you never need to
pass non-ASCII-punctuation here

State

Info passed around about the current state (TypeScript type).
Fields
β€” stack of constructs we’re in
  • indexStack (Array<number>)
β€” positions of child nodes in their parents
  • associationId ((node: Association) => string)
β€” get an identifier from an association to match it to others (see
[`Association`][association])
  • enter ((construct: ConstructName) => () => void)
β€” enter a construct (returns a corresponding exit function)
(see [`ConstructName`][constructname])
  • indentLines ((value: string, map: Map) => string)
β€” pad serialized markdown (see [`Map`][map])
  • containerFlow ((parent: Node, info: Info) => string)
β€” serialize flow children (see [`Info`][info])
  • containerPhrasing ((parent: Node, info: Info) => string)
β€” serialize phrasing children (see [`Info`][info])
  • createTracker ((info: Info) => Tracker)
β€” track positional info in the output (see [`Info`][info],
[`Tracker`][tracker])
  • safe ((value: string, config: SafeConfig) => string)
β€” make a string safe for embedding (see [`SafeConfig`][safeconfig])
β€” applied user configuration
β€” applied unsafe patterns
β€” applied join handlers
β€” call the configured handler for the given node
β€” applied handlers
  • bulletCurrent (string or undefined)
β€” list marker currently in use
  • bulletLastUsed (string or undefined)
β€” list marker previously in use

Tracker

Track positional info in the output (TypeScript type).
This info isn’t used yet but such functionality will allow line wrapping, source maps, etc.
Fields
  • current (() => Info)
β€” get current tracked info
  • shift ((value: number) => void)
β€” define a relative increased line shift (the typical indent for lines)
  • move ((value: string) => string)
β€” move past some generated markdown

Unsafe

Schema that defines when a character cannot occur (TypeScript type).
Fields
  • character (string)
β€” single unsafe character
optional)
β€” constructs where this is bad
optional)
β€” constructs where this is fine again
  • before (string, optional)
β€” `character` is bad when this is before it (cannot be used together with
`atBreak`)
  • after (string, optional)
β€” `character` is bad when this is after it
  • atBreak (boolean, optional)
β€” `character` is bad at a break (cannot be used together with `before`)

List of extensions

β€” directives
β€” frontmatter (YAML, TOML, more)
β€” GFM
β€” GFM autolink literals
β€” GFM footnotes
β€” GFM strikethrough
β€” GFM tables
β€” GFM task list items
β€” math
β€” MDX
β€” MDX expressions
β€” MDX JSX
β€” MDX ESM

Syntax

Markdown is serialized according to CommonMark but care is taken to format in such a way that the resulting markdown should work with most markdown parsers. Extensions can add support for custom syntax.

Syntax tree

The syntax tree is mdast.

Types

This package is fully typed with TypeScript. It exports the additional types ConstructName, ConstructNameMap, Handle, Handlers, Info Join, Map, Options, SafeConfig, State, and Unsafe.

Security

mdast-util-to-markdown will do its best to serialize markdown to match the syntax tree, but there are several cases where that is impossible. It’ll do its best, but complete roundtripping is impossible given that any value could be injected into the tree.
As markdown is sometimes used for HTML, and improper use of HTML can open you up to a cross-site scripting (XSS)xss attack, use of mdast-util-to-markdown and parsing it again later could potentially be unsafe. When parsing markdown afterwards and then going to HTML, use something like hast-util-sanitizehast-util-sanitize to make the tree safe.

Related

β€” parse markdown to mdast
β€” parse markdown
β€” process markdown

Contribute

See contributing.mdcontributing in syntax-tree/.githubhealth for ways to get started. See support.mdsupport for ways to get help.
This project has a code of conductcoc. By interacting with this repository, organization, or community you agree to abide by its terms.

License

MITlicense Β© Titus Wormerauthor