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

remark plugin to support frontmatter (YAML, TOML, and more)
https://github.com/remarkjs/remark-frontmatter

frontmatter markdown remark remark-plugin toml yaml

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remark plugin to support frontmatter (YAML, TOML, and more)

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README 

        
# remark-frontmatter



[![Build][build-badge]][build]

[![Coverage][coverage-badge]][coverage]

[![Downloads][downloads-badge]][downloads]

[![Size][size-badge]][size]

[![Sponsors][sponsors-badge]][collective]

[![Backers][backers-badge]][collective]

[![Chat][chat-badge]][chat]



**[remark][]** plugin to support frontmatter (YAML, TOML, and more).



## Contents



*   [What is this?](#what-is-this)

*   [When should I use this?](#when-should-i-use-this)

*   [Install](#install)

*   [Use](#use)

*   [API](#api)

    *   [`unified().use(remarkFrontmatter[, options])`](#unifieduseremarkfrontmatter-options)

    *   [`Options`](#options)

*   [Examples](#examples)

    *   [Example: different markers and fences](#example-different-markers-and-fences)

    *   [Example: frontmatter as metadata](#example-frontmatter-as-metadata)

    *   [Example: frontmatter in MDX](#example-frontmatter-in-mdx)

*   [Authoring](#authoring)

*   [HTML](#html)

*   [CSS](#css)

*   [Syntax](#syntax)

*   [Syntax tree](#syntax-tree)

*   [Types](#types)

*   [Compatibility](#compatibility)

*   [Security](#security)

*   [Related](#related)

*   [Contribute](#contribute)

*   [License](#license)



## What is this?



This package is a [unified][] ([remark][]) plugin to add support for YAML, TOML,

and other frontmatter.



Frontmatter is a metadata format in front of the content.

It’s typically written in YAML and is often used with markdown.



This plugin follow how GitHub handles frontmatter.

GitHub only supports YAML frontmatter, but this plugin also supports different

flavors (such as TOML).



## When should I use this?



You can use frontmatter when you want authors, that have some markup

experience, to configure where or how the content is displayed or supply

metadata about content, and know that the markdown is only used in places

that support frontmatter.

A good example use case is markdown being rendered by (static) site generators.



If you *just* want to turn markdown into HTML (with maybe a few extensions such

as frontmatter), we recommend [`micromark`][micromark] with

[`micromark-extension-frontmatter`][micromark-extension-frontmatter] instead.

If you don’t use plugins and want to access the syntax tree, you can use

[`mdast-util-from-markdown`][mdast-util-from-markdown] with

[`mdast-util-frontmatter`][mdast-util-frontmatter].



## Install



This package is [ESM only][esm].

In Node.js (version 16+), install with [npm][]:



```sh

npm install remark-frontmatter

```



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



```js

import remarkFrontmatter from 'https://esm.sh/remark-frontmatter@5'

```



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



```html



  import remarkFrontmatter from 'https://esm.sh/remark-frontmatter@5?bundle'



```



## Use



Say our document `example.md` contains:



```markdown

+++

layout = "solar-system"

+++



# Jupiter

```



…and our module `example.js` contains:



```js

import remarkFrontmatter from 'remark-frontmatter'

import remarkParse from 'remark-parse'

import remarkStringify from 'remark-stringify'

import {unified} from 'unified'

import {read} from 'to-vfile'



const file = await unified()

  .use(remarkParse)

  .use(remarkStringify)

  .use(remarkFrontmatter, ['yaml', 'toml'])

  .use(function () {

    return function (tree) {

      console.dir(tree)

    }

  })

  .process(await read('example.md'))



console.log(String(file))

```



…then running `node example.js` yields:



```js

{

  type: 'root',

  children: [

    {type: 'toml', value: 'layout = "solar-system"', position: [Object]},

    {type: 'heading', depth: 1, children: [Array], position: [Object]}

  ],

  position: {

    start: {line: 1, column: 1, offset: 0},

    end: {line: 6, column: 1, offset: 43}

  }

}

```



```markdown

+++

layout = "solar-system"

+++



# Jupiter

```



## API



This package exports no identifiers.

The default export is [`remarkFrontmatter`][api-remark-frontmatter].



### `unified().use(remarkFrontmatter[, options])`



Add support for frontmatter.



###### Parameters



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

    — configuration



###### Returns



Nothing (`undefined`).



###### Notes



Doesn’t parse the data inside them:

[create your own plugin][unified-create-plugin] to do that.



### `Options`



Configuration (TypeScript type).



###### Type



```ts

type Options = Array | Matter | Preset



/**

 * Sequence.

 *

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

 */

export type Info = {

  /**

   * Closing.

   */

  close: string

  /**

   * Opening.

   */

  open: string

}



/**

 * Fence configuration.

 */

type FenceProps = {

  /**

   * Complete fences.

   *

   * This can be used when fences contain different characters or lengths

   * other than 3.

   * Pass `open` and `close` to interface to specify different characters for opening and

   * closing fences.

   */

  fence: Info | string

  /**

   * If `fence` is set, `marker` must not be set.

   */

  marker?: never

}



/**

 * Marker configuration.

 */

type MarkerProps = {

  /**

   * Character repeated 3 times, used as complete fences.

   *

   * For example the character `'-'` will result in `'---'` being used as the

   * fence

   * Pass `open` and `close` to specify different characters for opening and

   * closing fences.

   */

  marker: Info | string

  /**

   * If `marker` is set, `fence` must not be set.

   */

  fence?: never

}



/**

 * Fields describing a kind of matter.

 *

 * > 👉 **Note**: using `anywhere` is a terrible idea.

 * > It’s called frontmatter, not matter-in-the-middle or so.

 * > This makes your markdown less portable.

 *

 * > 👉 **Note**: `marker` and `fence` are mutually exclusive.

 * > If `marker` is set, `fence` must not be set, and vice versa.

 */

type Matter = (MatterProps & FenceProps) | (MatterProps & MarkerProps)



/**

 * Fields describing a kind of matter.

 */

type MatterProps = {

  /**

   * Node type to tokenize as.

   */

  type: string

  /**

   * Whether matter can be found anywhere in the document, normally, only matter

   * at the start of the document is recognized.

   *

   * > 👉 **Note**: using this is a terrible idea.

   * > It’s called frontmatter, not matter-in-the-middle or so.

   * > This makes your markdown less portable.

   */

  anywhere?: boolean | null | undefined

}



/**

 * Known name of a frontmatter style.

 */

type Preset = 'toml' | 'yaml'

```



## Examples



### Example: different markers and fences



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"

}

```



### Example: frontmatter as metadata



This plugin handles the syntax of frontmatter in markdown.

It does not *parse* that frontmatter as say YAML or TOML and expose it

somewhere.



In unified, there is a place for metadata about files:

[`file.data`][vfile-file-data].

For frontmatter specifically, it’s customary to expose parsed data at `file.data.matter`.



We can make a plugin that does this.

This example uses the utility [`vfile-matter`][vfile-matter], which is specific

to YAML.

To support other data languages, look at this utility for inspiration.



`my-unified-plugin-handling-yaml-matter.js`:



```js

/**

 * @typedef {import('unist').Node} Node

 * @typedef {import('vfile').VFile} VFile

 */



import {matter} from 'vfile-matter'



/**

 * Parse YAML frontmatter and expose it at `file.data.matter`.

 *

 * @returns

 *   Transform.

 */

export default function myUnifiedPluginHandlingYamlMatter() {

  /**

   * Transform.

   *

   * @param {Node} tree

   *   Tree.

   * @param {VFile} file

   *   File.

   * @returns {undefined}

   *   Nothing.

   */

  return function (tree, file) {

    matter(file)

  }

}

```



…with an example markdown file `example.md`:



```markdown

---

key: value

---



# Venus

```



…and using the plugin with an `example.js` containing:



```js

import remarkParse from 'remark-parse'

import remarkFrontmatter from 'remark-frontmatter'

import remarkStringify from 'remark-stringify'

import {read} from 'to-vfile'

import {unified} from 'unified'

import myUnifiedPluginHandlingYamlMatter from './my-unified-plugin-handling-yaml-matter.js'



const file = await unified()

  .use(remarkParse)

  .use(remarkStringify)

  .use(remarkFrontmatter)

  .use(myUnifiedPluginHandlingYamlMatter)

  .process(await read('example.md'))



console.log(file.data.matter) // => {key: 'value'}

```



### Example: frontmatter in MDX



MDX has the ability to export data from it, where markdown does not.

When authoring MDX, you can write `export` statements and expose arbitrary data

through them.

It is also possible to write frontmatter, and let a plugin turn those into

export statements.



To automatically turn frontmatter into export statements, use

[`remark-mdx-frontmatter`][remark-mdx-frontmatter].



With an `example.mdx` as follows:



```mdx

---

key: value

---



# Mars

```



This plugin can be used as follows:



```js

import {compile} from '@mdx-js/mdx'

import remarkFrontmatter from 'remark-frontmatter'

import remarkMdxFrontmatter from 'remark-mdx-frontmatter'

import {read, write} from 'to-vfile'



const file = await compile(await read('example.mdx'), {

  remarkPlugins: [remarkFrontmatter, [remarkMdxFrontmatter, {name: 'matter'}]]

})

file.path = 'output.js'

await write(file)



const mod = await import('./output.js')

console.log(mod.matter) // => {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 [`remark-rehype`][remark-rehype] does.



## CSS



This package does not relate to CSS.



## Syntax



See [*Syntax* in

`micromark-extension-frontmatter`](https://github.com/micromark/micromark-extension-frontmatter#syntax).



## Syntax tree



See [*Syntax tree* in

`mdast-util-frontmatter`](https://github.com/syntax-tree/mdast-util-frontmatter#syntax-tree).



## Types



This package is fully typed with [TypeScript][].

It exports the additional type [`Options`][api-options].



The YAML node type is supported in `@types/mdast` by default.

To add other node types, register them by adding them to

`FrontmatterContentMap`:



```ts

import type {Data, Literal} from 'mdast'



interface Toml extends Literal {

  type: 'toml'

  data?: Data

}



declare module 'mdast' {

  interface FrontmatterContentMap {

    // Allow using TOML nodes defined by `remark-frontmatter`.

    toml: Toml

  }

}

```



## 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, `remark-frontmatter@^5`,

compatible with Node.js 16.



This plugin works with unified 6+ and remark 13+.



## Security



Use of `remark-frontmatter` does not involve **[rehype][]** ([hast][]) or user

content so there are no openings for [cross-site scripting (XSS)][wiki-xss]

attacks.



## Related



*   [`remark-yaml-config`](https://github.com/remarkjs/remark-yaml-config)

    — configure remark from YAML configuration

*   [`remark-gfm`](https://github.com/remarkjs/remark-gfm)

    — support GFM (autolink literals, footnotes, strikethrough, tables,

    tasklists)

*   [`remark-mdx`](https://github.com/mdx-js/mdx/tree/main/packages/remark-mdx)

    — support MDX (ESM, JSX, expressions)

*   [`remark-directive`](https://github.com/remarkjs/remark-directive)

    — support directives

*   [`remark-math`](https://github.com/remarkjs/remark-math)

    — support math



## Contribute



See [`contributing.md`][contributing] in [`remarkjs/.github`][health] 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/remarkjs/remark-frontmatter/workflows/main/badge.svg



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



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



[coverage]: https://codecov.io/github/remarkjs/remark-frontmatter



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



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



[size-badge]: https://img.shields.io/bundlejs/size/remark-frontmatter



[size]: https://bundlejs.com/?q=remark-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/remarkjs/remark/discussions



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



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



[esmsh]: https://esm.sh



[health]: https://github.com/remarkjs/.github



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



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



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



[license]: license



[author]: https://wooorm.com



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



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



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



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



[hast]: https://github.com/syntax-tree/hast



[rehype]: https://github.com/rehypejs/rehype



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



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



[remark-mdx-frontmatter]: https://github.com/remcohaszing/remark-mdx-frontmatter



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



[unified]: https://github.com/unifiedjs/unified



[unified-create-plugin]: https://unifiedjs.com/learn/guide/create-a-plugin/



[vfile-file-data]: https://github.com/vfile/vfile#filedata



[vfile-matter]: https://github.com/vfile/vfile-matter



[wiki-xss]: https://en.wikipedia.org/wiki/Cross-site_scripting



[api-options]: #options



[api-remark-frontmatter]: #unifieduseremarkfrontmatter-options