vfile-matter

vfile utility parse YAML front matter.

What is this?
When should I use this?
Install
Use
API
Types
Compatibility
Contribute
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, instead of stripping frontmatter.

Install

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

npm install vfile-matter

In Deno with esm.sh:

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

In browsers with esm.sh:

<script type="module">
  import {matter} from 'https://esm.sh/vfile-matter@5?bundle'
</script>

Use

Say our document example.html contains:

---
title: Hello, world!
---
<p>Some more text</p>

…and our module example.js looks as follows:

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:

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

<p>Some more text</p>

API

This package exports the identifier 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) — virtual file
options (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, default: {}) — configuration for the YAML parser, passed to yaml as x in yaml.parse('', x)

`YamlOptions`

Options for the YAML parser (TypeScript type).

Equivalent to the combination of ParseOptions, DocumentOptions, SchemaOptions, and ToJsOptions.

Type

type YamlOptions = ParseOptions &
  DocumentOptions &
  SchemaOptions &
  ToJsOptions

Types

This package is fully typed with TypeScript. It exports the additional types Options and YamlOptions.

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

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 in vfile/.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.

vfile/vfile-matter