micromark-extension-frontmatter

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[micromark][] extensions to support frontmatter (YAML, TOML, and more).

* What is this?
* When to use this
* Install
* Use
* API
* frontmatter(options?)
* frontmatterHtml(options?)
* toMatters(options?)
* Info
* Matter
* Options
* Preset
* Examples
* Authoring
* HTML
* CSS
* Syntax
* Types
* Compatibility
* Security
* Related
* Contribute
* License

What is this?

This package contains two extensions that add support for frontmatter syntax
as often used in markdown to [micromark][micromark].

Frontmatter is a metadata format in front of the content.
It’s typically written in YAML and is often used with markdown.
Frontmatter does not work everywhere so it makes markdown less portable.

As there is no spec for frontmatter in markdown, these extensions follow how
YAML frontmatter works on github.com.
It can also parse TOML frontmatter, just like YAML except that it uses a +.

When to use this

You can use these extensions when you are working with [micromark][micromark]
already.

When you need a syntax tree, you can combine this package with
[mdast-util-frontmatter][mdast-util-frontmatter].

All these packages are used [remark-frontmatter][remark-frontmatter], which
focusses on making it easier to transform content by abstracting these
internals away.

Install

This package is [ESM only][esm].
In Node.js (version 16+), install with [npm][]:

``sh npm install micromark-extension-frontmatter`

In Deno with [esm.sh][esmsh]:

`js import {frontmatter, frontmatterHtml} from 'https://esm.sh/micromark-extension-frontmatter@2'`

In browsers with [esm.sh][esmsh]:

`html`

`Use`

Say our module example.js looks as follows:

`js import {micromark} from 'micromark' import {frontmatter, frontmatterHtml} from 'micromark-extension-frontmatter'

const output = micromark('---\na: b\n---\n# c', { extensions: [frontmatter()], htmlExtensions: [frontmatterHtml()] })

console.log(output)`

…now running node example.js yields:

`html

`c`

API

This package exports the identifiers [frontmatter][api-frontmatter], [frontmatterHtml][api-frontmatter-html], and [toMatters][api-to-matters]. There is no default export.

The export map supports the [developmentcondition][development]. Runnode --conditions development module.jsto get instrumented dev code. Without this condition, production code is loaded.

`$3`

Create an extension for [micromark][micromark] to enable frontmatter syntax.

###### Parameters

* options ([Options][api-options], default: ['yaml']) — configuration

###### Returns

Extension for micromark that can be passed in extensions, to enable frontmatter syntax ([Extension][micromark-extension]).

`$3`

Create an extension for micromarkto support frontmatter when serializing to HTML.

> 👉 Note: this makes sure nothing is generated in the output HTML for > frontmatter.

###### Parameters

* options ([Options][api-options], default: ['yaml']) — configuration

###### Returns

Extension for micromark that can be passed in htmlExtensions, to support frontmatter when serializing to HTML ([HtmlExtension][micromark-html-extension]).

`$3`

Simplify options by normalizing them to an array of matters.

###### Parameters

* options ([Options][api-options], default: ['yaml']) — configuration

###### Returns

List of matters ([Array][api-matter]).

`$3`

Sequence (TypeScript type).

Depending on how this structure is used, it reflects a marker or a fence.

###### Fields

* open (string) — opening *close (string) — closing

`$3`

Fields describing a kind of matter (TypeScript type).

> 👉 Note: using anywhereis a terrible idea. > It’s called frontmatter, not matter-in-the-middle or so. > This makes your markdown less portable.

> 👉 Note: marker and fenceare mutually exclusive. > Ifmarker is set, fence must not be set, and vice versa.

###### Fields

* type (string) — node type to tokenize as *marker (string or [Info][api-info]) — character repeated 3 times, used as complete fences *fence (string or [Info][api-info]) — complete fences *anywhere (boolean, default: false) — whether matter can be found anywhere in the document, normally only matter at the start of the document is recognized

`$3`

Configuration (TypeScript type).

###### Type

`ts type Options = Array | Matter | Preset`

`$3`

Known name of a frontmatter style (TypeScript type).

* 'yaml' — [Matter][api-matter] defined as {type: 'yaml', marker: '-'}*'toml' — [Matter][api-matter] defined as {type: 'toml', marker: '+'}

###### Type

`ts type Preset = 'toml' | 'yaml'`

`Examples`

Here are a couple of example of different matter objects and what frontmatter they match.

To match frontmatter with the same opening and closing fence, namely three of the same markers, use for example{type: 'yaml', marker: '-'}, which matches:

`yaml --- key: value ---`

To match frontmatter with different opening and closing fences, which each use three different markers, use for example{type: 'custom', marker: {open: '<', close: '>'}}, which matches:

`text <<< data >>>`

To match frontmatter with the same opening and closing fences, which both use the same custom string, use for example{type: 'custom', fence: '+=+=+=+'}, which matches:

`text +=+=+=+ data +=+=+=+`

To match frontmatter with different opening and closing fences, which each use different custom strings, use for example{type: 'json', fence: {open: '{', close: '}'}}, which matches:

`json { "key": "value" }`

`Authoring`

When authoring markdown with frontmatter, it’s recommended to use YAML frontmatter if possible. While YAML has some warts, it works in the most places, so using it guarantees the highest chance of portability.

In certain ecosystems, other flavors are widely used. For example, in the Rust ecosystem, TOML is often used. In such cases, using TOML is an okay choice.

When possible, do not use other types of frontmatter, and do not allow frontmatter anywhere.

`HTML`

Frontmatter does not relate to HTML elements. It is typically stripped, which is what these extensions do.

`CSS`

This package does not relate to CSS.

`Syntax`

Frontmatter forms with the following BNF:

`bnf frontmatter ::= fence_open ( eol line ) eol fence_close fence_open ::= sequence_open *space_or_tab fence_close ::= sequence_close *space_or_tab ; Note: options can define custom sequences. sequence_open ::= 3'+' | 3'-' ; Note: options can define custom sequences. ; Restriction:sequence_close must correspond to sequence_open. sequence_close ::= 3'+' | 3'-'

; Character groups for informational purposes. byte ::= 0x00..=0xFFFF eol ::= '\n' | '\r' | '\r\n' line ::= byte - eol`

Frontmatter can only occur once. It cannot occur in a container. It must have a closing fence. Like flow constructs, it must be followed by an eol (line ending) or eof (end of file).

`Types`

This package is fully typed with [TypeScript][]. It exports the additional types [Info][api-info], [Matter][api-matter], [Options][api-options], [Preset][api-preset].

`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,micromark-extension-frontmatter@^2, compatible with Node.js 16.

This package works with micromark version 3 and later.

`Security`

This package is safe.

`Related`

* [remark-frontmatter][remark-frontmatter] — remark plugin using this to support frontmatter * [mdast-util-frontmatter][mdast-util-frontmatter] — mdast utility to support frontmatter

`Contribute`

See [contributing.md in micromark/.github][contributing] for ways to get started. See [support.md`][support] for ways to get help.

This project has a [code of conduct][coc].
By interacting with this repository, organization, or community you agree to
abide by its terms.

License

[MIT][license] © [Titus Wormer][author]

[build-badge]: https://github.com/micromark/micromark-extension-frontmatter/workflows/main/badge.svg

[build]: https://github.com/micromark/micromark-extension-frontmatter/actions

[coverage-badge]: https://img.shields.io/codecov/c/github/micromark/micromark-extension-frontmatter.svg

[coverage]: https://codecov.io/github/micromark/micromark-extension-frontmatter

[downloads-badge]: https://img.shields.io/npm/dm/micromark-extension-frontmatter.svg

[downloads]: https://www.npmjs.com/package/micromark-extension-frontmatter

[size-badge]: https://img.shields.io/badge/dynamic/json?label=minzipped%20size&query=$.size.compressedSize&url=https://deno.bundlejs.com/?q=micromark-extension-frontmatter

[size]: https://bundlejs.com/?q=micromark-extension-frontmatter

[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg

[backers-badge]: https://opencollective.com/unified/backers/badge.svg

[collective]: https://opencollective.com/unified

[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg

[chat]: https://github.com/micromark/micromark/discussions

[npm]: https://docs.npmjs.com/cli/install

[esmsh]: https://esm.sh

[license]: license

[author]: https://wooorm.com

[contributing]: https://github.com/micromark/.github/blob/main/contributing.md

[support]: https://github.com/micromark/.github/blob/main/support.md

[coc]: https://github.com/micromark/.github/blob/main/code-of-conduct.md

[esm]: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

[typescript]: https://www.typescriptlang.org

[development]: https://nodejs.org/api/packages.html#packages_resolving_user_conditions

[micromark]: https://github.com/micromark/micromark

[mdast-util-frontmatter]: https://github.com/syntax-tree/mdast-util-frontmatter

[remark-frontmatter]: https://github.com/remarkjs/remark-frontmatter

[micromark-extension]: https://github.com/micromark/micromark#syntaxextension

[micromark-html-extension]: https://github.com/micromark/micromark#htmlextension

[api-frontmatter]: #frontmatteroptions

[api-frontmatter-html]: #frontmatterhtmloptions

[api-to-matters]: #tomattersoptions

[api-info]: #info

[api-matter]: #matter

[api-options]: #options

[api-preset]: #preset

micromark-extension-frontmatter

[micromark][] extensions to support frontmatter (YAML, TOML, and more).

What is this?

This package contains two extensions that add support for frontmatter syntax
as often used in markdown to [micromark][micromark].

Frontmatter is a metadata format in front of the content.
It’s typically written in YAML and is often used with markdown.
Frontmatter does not work everywhere so it makes markdown less portable.

As there is no spec for frontmatter in markdown, these extensions follow how
YAML frontmatter works on github.com.
It can also parse TOML frontmatter, just like YAML except that it uses a +.

When to use this

You can use these extensions when you are working with [micromark][micromark]
already.

When you need a syntax tree, you can combine this package with
[mdast-util-frontmatter][mdast-util-frontmatter].

All these packages are used [remark-frontmatter][remark-frontmatter], which
focusses on making it easier to transform content by abstracting these
internals away.

Install

This package is [ESM only][esm].
In Node.js (version 16+), install with [npm][]:

``sh npm install micromark-extension-frontmatter`

In Deno with [esm.sh][esmsh]:

`js import {frontmatter, frontmatterHtml} from 'https://esm.sh/micromark-extension-frontmatter@2'`

In browsers with [esm.sh][esmsh]:

`html`

`Use`

Say our module example.js looks as follows:

`js import {micromark} from 'micromark' import {frontmatter, frontmatterHtml} from 'micromark-extension-frontmatter'

const output = micromark('---\na: b\n---\n# c', { extensions: [frontmatter()], htmlExtensions: [frontmatterHtml()] })

console.log(output)`

…now running node example.js yields:

`html

`c`

API