vfile-matter
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.