11 KiB
mdast-util-frontmatter
mdast extensions to parse and serialize frontmatter (YAML, TOML, and more).
Contents
- What is this?
- When to use this
- Install
- Use
- API
- Syntax
- Syntax tree
- Types
- Compatibility
- Related
- Contribute
- License
What is this?
This package contains two extensions that add support for frontmatter syntax
as often used in markdown to mdast.
These extensions plug into
mdast-util-from-markdown (to support parsing
frontmatter in markdown into a syntax tree) and
mdast-util-to-markdown (to support serializing
frontmatter in syntax trees to markdown).
Frontmatter is a metadata format in front of the content. It’s typically written in YAML and is often used with markdown. Frontmatter does not work everywhere so it makes markdown less portable.
These extensions follow how GitHub handles frontmatter. GitHub only supports YAML frontmatter, but these extensions also support different flavors (such as TOML).
When to use this
You can use these extensions when you are working with
mdast-util-from-markdown and mdast-util-to-markdown already.
When working with mdast-util-from-markdown, you must combine this package
with micromark-extension-frontmatter.
When you don’t need a syntax tree, you can use micromark
directly with
micromark-extension-frontmatter.
All these packages are used remark-frontmatter, which
focusses on making it easier to transform content by abstracting these
internals away.
Install
This package is ESM only. In Node.js (version 16+), install with npm:
npm install mdast-util-frontmatter
In Deno with esm.sh:
import {frontmatterFromMarkdown, frontmatterToMarkdown} from 'https://esm.sh/mdast-util-frontmatter@2'
In browsers with esm.sh:
<script type="module">
import {frontmatterFromMarkdown, frontmatterToMarkdown} from 'https://esm.sh/mdast-util-frontmatter@2?bundle'
</script>
Use
Say our document example.md contains:
+++
title = "New Website"
+++
# Other markdown
…and our module example.js looks as follows:
import fs from 'node:fs/promises'
import {frontmatter} from 'micromark-extension-frontmatter'
import {fromMarkdown} from 'mdast-util-from-markdown'
import {frontmatterFromMarkdown, frontmatterToMarkdown} from 'mdast-util-frontmatter'
import {toMarkdown} from 'mdast-util-to-markdown'
const doc = await fs.readFile('example.md')
const tree = fromMarkdown(doc, {
extensions: [frontmatter(['yaml', 'toml'])],
mdastExtensions: [frontmatterFromMarkdown(['yaml', 'toml'])]
})
console.log(tree)
const out = toMarkdown(tree, {extensions: [frontmatterToMarkdown(['yaml', 'toml'])]})
console.log(out)
…now running node example.js yields (positional info removed for brevity):
{
type: 'root',
children: [
{type: 'toml', value: 'title = "New Website"'},
{
type: 'heading',
depth: 1,
children: [{type: 'text', value: 'Other markdown'}]
}
]
}
+++
title = "New Website"
+++
# Other markdown
API
This package exports the identifiers
frontmatterFromMarkdown and
frontmatterToMarkdown.
There is no default export.
frontmatterFromMarkdown(options?)
Create an extension for
mdast-util-from-markdown.
Parameters
options(Options, optional) — configuration
Returns
Extension for mdast-util-from-markdown
(FromMarkdownExtension).
frontmatterToMarkdown(options?)
Create an extension for
mdast-util-to-markdown.
Parameters
options(Options, optional) — configuration
Returns
Extension for mdast-util-to-markdown
(ToMarkdownExtension).
Info
Structure of marker or fence (TypeScript type).
Same as Info from micromark-extension-frontmatter.
Matter
Structure of matter (TypeScript type).
Same as Matter from micromark-extension-frontmatter.
Options
Configuration (TypeScript type).
Same as Options from micromark-extension-frontmatter.
Syntax
See Syntax in micromark-extension-frontmatter.
Syntax tree
The following interfaces are added to mdast by this utility.
Nodes
👉 Note: other nodes are not enabled by default, but when passing options to enable them, they work the same as YAML.
YAML
interface YAML <: Literal {
type: "yaml"
}
YAML (Literal) represents a collection of metadata for the document in the YAML data serialization language.
YAML can be used where frontmatter content
is expected.
Its content is represented by its value field.
For example, the following markdown:
---
foo: bar
---
Yields:
{type: 'yaml', value: 'foo: bar'}
Content model
FrontmatterContent
type FrontmatterContent = YAML
Frontmatter content represent out-of-band information about the document.
If frontmatter is present, it must be limited to one node in the tree, and can only exist as a head.
FlowContent (frontmatter)
type FlowContentFrontmatter = FrontmatterContent | FlowContent
Types
This package is fully typed with TypeScript.
It exports the additional types Info, Matter,
and Options.
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 `mdast-util-frontmatter`.
toml: Toml
}
}
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,
mdast-util-frontmatter@^2, compatible with Node.js 16.
This utility works with mdast-util-from-markdown version 2+ and
mdast-util-to-markdown version 2+.
Related
remark-frontmatter— remark plugin to support frontmattermicromark-extension-frontmatter— micromark extension to parse frontmatter
Contribute
See contributing.md in syntax-tree/.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.