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

utility to parse the YAML front matter in a vfile
https://github.com/vfile/vfile-matter

file frontmatter matter vfile vfile-util virtual yaml

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utility to parse the YAML front matter in a vfile

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README 

        
# vfile-matter



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[vfile][] utility parse YAML front matter.



## Contents



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

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

*   [Install](#install)

*   [Use](#use)

*   [API](#api)

    *   [`matter(file[, options])`](#matterfile-options)

    *   [`Options`](#options)

    *   [`YamlOptions`](#yamloptions)

*   [Types](#types)

*   [Compatibility](#compatibility)

*   [Contribute](#contribute)

*   [License](#license)



## What is this?



This package parses YAML frontmatter, when found in a file, and exposes it as

`file.data.matter`.

It can optionally strip the frontmatter, which is useful for languages that do

not understand frontmatter, but stripping can make it harder to deal with

languages that *do* understand it, such as markdown, because it messes up

positional info of warnings and errors.



## When should I use this?



Frontmatter is a metadata format in front of content.

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

This mechanism works well when you want authors, that have some markup

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

metadata about content.



When using vfiles with markdown, you are likely also using [remark][], in which

case you should use [`remark-frontmatter`][remark-frontmatter], instead of

stripping frontmatter.



## Install



This package is [ESM only][esm].

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



```sh

npm install vfile-matter

```



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



```js

import {matter} from 'https://esm.sh/vfile-matter@5'

```



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



```html



  import {matter} from 'https://esm.sh/vfile-matter@5?bundle'



```



## Use



Say our document `example.html` contains:



```html

---

title: Hello, world!

---

Some more text


```



…and our module `example.js` looks as follows:



```js

import {read} from 'to-vfile'

import {matter} from 'vfile-matter'



const file = await read('example.html')



matter(file, {strip: true})



console.log(file.data)

console.log(String(file))

```



…now running `node example.js` yields:



```js

{matter: {title: 'Hello, world!'}}

```



```html

Some more text


```



## API



This package exports the identifier [`matter`][api-matter].

There is no default export.



### `matter(file[, options])`



Parse the YAML front matter in a file and expose it as `file.data.matter`.



If no matter is found in the file, nothing happens, except that

`file.data.matter` is set to an empty object (`{}`).



If the file value is an `Uint8Array`, assumes it is encoded in UTF-8.



###### Parameters



*   `file` ([`VFile`][vfile])

    — virtual file

*   `options` ([`Options`][api-options], default: `{}`)

    — configuration



###### Returns



Nothing (`undefined`).



### `Options`



Configuration (TypeScript type).



###### Fields



*   `strip` (`boolean`, default: `false`).

    — remove the YAML front matter from the file

*   `yaml` ([`YamlOptions`][api-yaml-options], default: `{}`)

    — configuration for the YAML parser, passed to [`yaml`][yaml] as `x` in

    `yaml.parse('', x)`



### `YamlOptions`



Options for the YAML parser (TypeScript type).



Equivalent to the combination of

[`ParseOptions`](https://eemeli.org/yaml/#parse-options),

[`DocumentOptions`](https://eemeli.org/yaml/#document-options),

[`SchemaOptions`](https://eemeli.org/yaml/#schema-options), and

[`ToJsOptions`](https://eemeli.org/yaml/#tojs-options).



###### Type



```ts

type YamlOptions = ParseOptions &

  DocumentOptions &

  SchemaOptions &

  ToJsOptions

```



## Types



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

It exports the additional types [`Options`][api-options] and

[`YamlOptions`][api-yaml-options].



To type `file.data.matter`, you can augment `DataMap` from `vfile` as follows:



```ts

declare module 'vfile' {

  interface DataMap {

    matter: {

      // `file.data.matter.string` is typed as `string | undefined`.

      title?: string | undefined

    }

  }

}



export {} // You may not need this, but it makes sure the file is a module.

```



## 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, `vfile-matter@^5`,

compatible with Node.js 16.



## Contribute



See [`contributing.md`][contributing] in [`vfile/.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/vfile/vfile-matter/workflows/main/badge.svg



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



[coverage-badge]: https://img.shields.io/codecov/c/github/vfile/vfile-matter.svg



[coverage]: https://codecov.io/github/vfile/vfile-matter



[downloads-badge]: https://img.shields.io/npm/dm/vfile-matter.svg



[downloads]: https://www.npmjs.com/package/vfile-matter



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



[size]: https://bundlejs.com/?q=vfile-matter



[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/vfile/vfile/discussions



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



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



[esmsh]: https://esm.sh



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



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



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



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



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



[license]: license



[author]: https://wooorm.com



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



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



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



[yaml]: https://github.com/eemeli/yaml



[api-matter]: #matterfile-options



[api-options]: #options



[api-yaml-options]: #yamloptions