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mdast-util-to-markdown

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mdast utility to parse markdown.

When to use this

Use this if you have direct access to an AST and need to serialize it. Use remark instead, which includes this, but has a nice interface and hundreds of plugins.

Install

This package is ESM only: Node 12+ is needed to use it and it must be imported instead of required.

npm:

npm install mdast-util-to-markdown

Use

Say we have the following script, example.js:

import {toMarkdown} from 'mdast-util-to-markdown'

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 yields (note the properly escaped characters which would otherwise turn into a list and image respectively):

> ***
>
> \- a
> b \![d](example.com)

API

This package exports the following identifier: toMarkdown. There is no default export.

toMarkdown(tree[, options])

Serialize mdast to markdown.

Formatting options
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 doesnt work ('*', '+', or '-', default: depends).

There are three cases where the primary bullet cant 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 doesnt work ('.' or ')', default: none).

There is one case where the primary bullet for ordered items cant 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 to serialize emphasis ('*' or '_', default: '*').

options.fence

Marker to use to serialize fenced code ('`' or '~', default: '`').

options.fences

Whether to use fenced code always (boolean, default: false). The default is to fenced code if there is a language defined, if the code is empty, or if it starts or ends in empty lines.

options.incrementListMarker

Whether to increment the value of bullets of items in ordered lists (boolean, default: true).

options.listItemIndent

Whether to indent the content of list items with the size of the bullet plus one space (when 'one') or 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) ('one', 'tab', or 'mixed', default: 'tab').

options.quote

Marker to use to serialize titles ('"' or "'", default: '"').

options.resourceLink

Whether to use resource links ([text](url)) always (boolean, default: false). The default is to use autolinks (<https://example.com>) when possible.

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). Setext headings are not possible for headings with a rank more than 2 or when theyre empty.

options.strong

Marker to use to serialize strong ('*' or '_', default: '*').

options.tightDefinitions

Whether to join definitions w/o a blank line (boolean, default: false). Shortcut for a join function like so:

function (left, right) {
  if (left.type === 'definition' && right.type === 'definition') {
    return 0
  }
}
options.handlers

Object mapping node types to custom handlers. Useful for syntax extensions. Take a look at lib/handle for examples.

options.join

List of functions used to determine what to place between two flow nodes. Often, they are joined by one blank line. In certain cases, its nicer to have them next to each other. Or, they cant occur together. These functions receive two adjacent nodes and their parent and can return number or boolean, referring to how many blank lines to use between them. A return value of true is as passing 1. A return value of 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
options.unsafe

List of patterns to escape. Useful for syntax extensions. Take a look at lib/unsafe.js for examples.

Extension options
options.extensions

List of extensions (Array.<ToMarkdownExtension>). Each ToMarkdownExtension is an object with the same interface as options here.

Returns

string Serialized markdown.

List of extensions

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. Itll 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) 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-sanitize to make the tree safe.

Related

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


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