unified

Project: remarkjs/remark-frontmatter

Package: remark-frontmatter@4.0.1

  1. Dependents: 0
  2. remark plugin to support frontmatter (yaml, toml, and more)
  1. remark 205
  2. unified 179
  3. markdown 151
  4. plugin 138
  5. mdast 88
  6. remark-plugin 75
  7. frontmatter 7
  8. yaml 7
  9. toml 4

remark-frontmatter

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

Contents

What is this?

This package is a unified (remark) plugin to add support for YAML, TOML, and other frontmatter. You can use this to add support for parsing and serializing this syntax extension.

unified is a project that transforms content with abstract syntax trees (ASTs). remark adds support for markdown to unified. mdast is the markdown AST that remark uses. micromark is the markdown parser we use. This is a remark plugin that adds support for the frontmatter syntax and AST to remark.

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. Frontmatter does not work everywhere so it makes markdown less portable. A good example use case is markdown being rendered by (static) site generators.

Install

This package is ESM only. In Node.js (version 12.20+, 14.14+, or 16.0+), install with npm:

npm install remark-frontmatter

In Deno with esm.sh:

import remarkFrontmatter from 'https://esm.sh/remark-frontmatter@4'

In browsers with esm.sh:

<script type="module">
  import remarkFrontmatter from 'https://esm.sh/remark-frontmatter@4?bundle'
</script>

Use

Say we have the following file, example.md:

+++
title = "New Website"
+++

# Other markdown

And our module, example.js, looks as follows:

import {read} from 'to-vfile'
import {unified} from 'unified'
import remarkParse from 'remark-parse'
import remarkFrontmatter from 'remark-frontmatter'
import remarkStringify from 'remark-stringify'

main()

async function main() {
  const file = await unified()
    .use(remarkParse)
    .use(remarkStringify)
    .use(remarkFrontmatter, ['yaml', 'toml'])
    .use(() => (tree) => {
      console.dir(tree)
    })
    .process(await read('example.md'))

  console.log(String(file))
}

Now, running node example yields:

{
  type: 'root',
  children: [
    {type: 'toml', value: 'title = "New Website"', position: [Object]},
    {type: 'heading', depth: 1, children: [Array], position: [Object]}
  ],
  position: {
    start: {line: 1, column: 1, offset: 0},
    end: {line: 6, column: 1, offset: 48}
  }
}
+++
title = "New Website"
+++

# Other markdown

API

This package exports no identifiers. The default export is remarkFrontmatter.

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

Configures remark so that it can parse and serialize frontmatter (YAML, TOML, and more). Doesn’t parse the data inside them: create your own plugin to do that.

options

One preset or Matter, or an array of them, defining all the supported frontmatters (default: 'yaml').

preset

Either 'yaml' or 'toml':

Matter

An object with a type and either a marker or a fence:

Examples

Example: custom marker

A custom frontmatter with different open and close markers, repeated 3 times, that looks like this:

<<<
data
>>>

# hi

…can be supported with:

// …
.use(remarkFrontmatter, {type: 'custom', marker: {open: '<', close: '>'}})
// …

Example: custom fence

A custom frontmatter with custom fences that are not repeated like this:

{
  "key": "value"
}

# hi

…can be supported with:

// …
.use(remarkFrontmatter, {type: 'json', fence: {open: '{', close: '}'}})
// …

Syntax

This plugin applies a micromark extensions to parse the syntax. See its readme for how it works:

The syntax supported depends on the given configuration.

Syntax tree

This plugin applies one mdast utility to build and serialize the AST. See its readme for how it works:

The node types supported in the tree depend on the given configuration.

Types

This package is fully typed with TypeScript. The YAML node type is supported in @types/mdast by default. To add other node types, register them by adding them to FrontmatterContentMap:

import type {Literal} from 'mdast'

interface TOML extends Literal {
  type: 'toml'
}

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 all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, and 16.0+. Our projects sometimes work with older versions, but this is not guaranteed.

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

Security

Use of remark-frontmatter does not involve rehype (hast) or user content so there are no openings for cross-site scripting (XSS) attacks.

Contribute

See contributing.md in remarkjs/.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