micromark-extension-frontmatter
micromark extension to support frontmatter (YAML, TOML, etc).
Contents
- What is this?
- When to use this
- Install
- Use
- API
- Examples
- Authoring
- HTML
- CSS
- Syntax
- Types
- Compatibility
- Security
- Related
- Contribute
- License
What is this?
This package contains extensions that add support for frontmatter.
As there is no spec for frontmatter in markdown, this extension follows how YAML frontmatter works on github.com. For the HTML part, instead of rendering YAML, it is ignored. Other types of frontmatter can be parsed, which will by default also work the same as on github.com.
When to use this
These tools are all low-level. In many cases, you want to use remark-frontmatter
with remark instead.
When you do want to use micromark
, you can use this. When working with mdast-util-from-markdown
, you must combine this package with mdast-util-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 micromark-extension-frontmatter
In Deno with esm.sh
:
import {frontmatter, frontmatterHtml} from 'https://esm.sh/micromark-extension-frontmatter@1'
In browsers with esm.sh
:
<script type="module">
import {frontmatter, frontmatterHtml} from 'https://esm.sh/micromark-extension-frontmatter@1?bundle'
</script>
Use
import {micromark} from 'micromark'
import {frontmatter, frontmatterHtml} from 'micromark-extension-frontmatter'
const output = micromark('---\na: b\n---\n# c', {
extensions: [frontmatter()],
htmlExtensions: [frontmatterHtml()]
})
console.log(output)
Yields:
<h1>c</h1>
API
This package exports the identifiers frontmatter
and frontmatterHtml
. There is no default export.
The export map supports the endorsed development
condition. Run node --conditions development module.js
to get instrumented dev code. Without this condition, production code is loaded.
frontmatter(options?)
Add support for parsing frontmatter in markdown.
Function that can be called to get a syntax extension for micromark (passed in extensions
).
Supports YAML by default. Can be configured to support TOML and more.
options
Configuration (optional).
One preset
or Matter
, or an array of them, defining all the supported frontmatters (default: 'yaml'
).
preset
Either 'yaml'
or 'toml'
:
'yaml'
—Matter
defined as{type: 'yaml', marker: '-'}
'toml'
—Matter
defined as{type: 'toml', marker: '+'}
Matter
An object with a type
and either a marker
or a fence
:
type
(string
) — type to tokenize asmarker
(string
or{open: string, close: string}
) — character used to construct fences. By providing an object withopen
andclose
different characters can be used for opening and closing fences. For example the character'-'
will result in'---'
being used as the fencefence
(string
or{open: string, close: string}
) — string used as the complete fence. By providing an object withopen
andclose
different values can be used for opening and closing fences. This can be used too if fences contain different characters or lengths other than 3anywhere
(boolean
, default:false
) – iftrue
, matter can be found anywhere in the document. Iffalse
(default), only matter at the start of the document is recognized
frontmatterHtml(options?)
Add support for turning frontmatter in markdown to HTML.
Function that can be called to get an HTML extension for micromark (passed in htmlExtensions
).
This makes sure nothing is generated for frontmatter.
Supports YAML by default. Can be configured to support other things.
See options
above for more info.
Examples
Here are a couple of example of different matter objects and what frontmatter they match.
To match frontmatter with the same opening and closing fence, namely three of the same markers, use for example {type: 'yaml', marker: '-'}
, which matches:
---
key: value
---
To match frontmatter with different opening and closing fences, which each use three different markers, use for example {type: 'custom', marker: {open: '<', close: '>'}}
, which matches:
<<<
data
>>>
To match frontmatter with the same opening and closing fences, which both use the same custom string, use for example {type: 'custom', fence: '+=+=+=+'}
, which matches:
+=+=+=+
data
+=+=+=+
To match frontmatter with different opening and closing fences, which each use different custom strings, use for example {type: 'json', fence: {open: '{', close: '}'}}
, which matches:
{
"key": "value"
}
Authoring
When authoring markdown with frontmatter, it’s recommended to use YAML frontmatter if possible. While YAML has some warts, it works in the most places, so using it guarantees the highest chance of portability.
In certain ecosystems, other flavors are widely used. For example, in the Rust ecosystem, TOML is often used. In such cases, using TOML is an okay choice.
When possible, do not use other types of frontmatter, and do not allow frontmatter anywhere.
HTML
Frontmatter does not relate to HTML elements. It is typically stripped, which is what this plugin does.
CSS
This package does not relate to CSS.
Syntax
Frontmatter forms with, roughly, the following BNF:
; Note: `fence` is an arbitrary, configured, fence.
frontmatter ::= fence *space_or_tab eol *( *code eol ) fence *space_or_tab
Types
This package is fully typed with TypeScript. It exports the additional type Options
.
Compatibility
This package is at least compatible with all maintained versions of Node.js. As of now, that is Node.js 12.20+, 14.14+, 16.0+, and 18.0+. It also works in Deno and modern browsers.
Security
This package is safe.
Related
remarkjs/remark-frontmatter
— remark plugin using this to support frontmattersyntax-tree/mdast-util-frontmatter
— mdast utility to support frontmatter
Contribute
See contributing.md
in micromark/.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.