unified

Project: vfile/vfile-matter

Package: vfile-matter@4.0.0

  1. Dependents: 0
  2. vfile utility to parse the YAML front matter in a file
  1. util 147
  2. utility 143
  3. file 34
  4. virtual 19
  5. vfile 17
  6. vfile-util 15
  7. frontmatter 7
  8. yaml 7

vfile-matter

Build Coverage Downloads Size Sponsors Backers Chat

vfile utility parse YAML front matter.

Contents

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 12.20+, 14.14+, 16.0+, or 18.0+), install with npm:

npm install vfile-matter

In Deno with esm.sh:

import {matter} from 'https://esm.sh/vfile-matter@4'

In browsers with esm.sh:

<script type="module">
  import {matter} from 'https://esm.sh/vfile-matter@4?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 vfile, and add 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 ({}).

options

Configuration (optional).

options.strip

Remove the YAML front matter from the file (boolean, default: false).

options.yaml

Options for the YAML parser (default: {}). These are passed to yaml as x in yaml.parse('', x), which is equivalent to the combination of ParseOptions, DocumentOptions, SchemaOptions, and ToJsOptions.

Returns

The given file (VFile).

Types

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

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?`.
      title?: string
    }
  }
}

Compatibility

Projects maintained by the unified collective are compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, 16.0+, and 18.0+. Our projects sometimes work with older versions, but this is not guaranteed.

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.

License

MIT © Titus Wormer