gray-matter-ts

Parse front-matter from a string or file. Fast, reliable and easy to use. Parses YAML front matter by default, but also has support for YAML, JSON, TOML or Coffee Front-Matter, with options to set custom delimiters. Used by metalsmith, assemble, verb and many other projects.

[!IMPORTANT] This is a fork of gray-matter, but it's written in Typescript. Thanks to jonschlinkert for the original project.

Install

# npm
npm install gray-matter-ts
# pnpm
pnpm add gray-matter-ts
# yarn
yarn add gray-matter-ts

What does this do?

Add the HTML in the following example to example.html, then add the following code to example.js and run $ node example (without the $):

import fs from 'node:fs'
import { matter } from 'gray-matter-ts'

const str = fs.readFileSync('example.html', 'utf8')
console.log(matter(str))

Converts a string with front-matter, like this:

---
title: Hello
slug: home
---
<h1>Hello world!</h1>

Into an object like this:

const file = {
  content: '<h1>Hello world!</h1>',
  data: {
    title: 'Hello',
    slug: 'home'
  }
}

Why use gray-matter-ts?

• simple: main function takes a string and returns an object
• accurate: better at catching and handling edge cases than front-matter parsers that rely on regex for parsing
• fast: faster than other front-matter parsers that use regex for parsing
• flexible: By default, gray-matter is capable of parsing YAML, JSON. But other engines may be added.
• extensible: Use custom delimiters, or add support for any language, like TOML, CoffeeScript, or CSON

Why did we create gray-matter in the first place?

We created gray-matter after trying out other libraries that failed to meet our standards and requirements.

Some libraries met most of the requirements, but none met all of them.

Here are the most important:

• Be usable, if not simple
• Use a dependable and well-supported library for parsing YAML
• Support other languages besides YAML
• Support stringifying back to YAML or another language
• Don't fail when no content exists
• Don't fail when no front matter exists
• Don't use regex for parsing. This is a relatively simple parsing operation, and regex is the slowest and most error-prone way to do it.
• Have no problem reading YAML files directly
• Have no problem with complex content, including non-front-matter fenced code blocks that contain examples of YAML front matter. Other parsers fail on this.
• Support stringifying back to front-matter. This is useful for linting, updating properties, etc.
• Allow custom delimiters, when it's necessary for avoiding delimiter collision.
• Should return an object with at least these three properties:
  • data: the parsed YAML front matter, as a JSON object
  • content: the contents as a string, without the front matter
  • orig: the "original" content (for debugging)

Usage

import { matter } from 'gray-matter-ts'

Pass a string and options to gray-matter:

console.log(matter('---\ntitle: Front Matter\n---\nThis is content.'))

Returns:

const file = {
  content: '\nThis is content.',
  data: {
    title: 'Front Matter'
  }
}

More about the returned object in the following section.

Returned object

gray-matter returns a file object with the following properties.

Enumerable

• file.data {Object}: the object created by parsing front-matter
• file.content {String}: the input string, with matter stripped
• file.excerpt {String}: an excerpt, if defined on the options
• file.empty {String}: when the front-matter is "empty" (either all whitespace, nothing at all, or just comments and no data), the original string is set on this property. See #65 for details regarding use case.
• file.isEmpty {Boolean}: true if front-matter is empty.

Non-enumerable

In addition, the following non-enumberable properties are added to the object to help with debugging.

• file.orig {Buffer}: the original input string (or buffer)
• file.language {String}: the front-matter language that was parsed. yaml is the default
• file.matter {String}: the raw, un-parsed front-matter string
• file.stringify {Function}: stringify the file by converting file.data to a string in the given language, wrapping it in delimiters and prepending it to file.content.

Run the examples

If you'd like to test-drive the examples, first clone gray-matter into my-project (or wherever you want):

git clone https://github.com/pengzhanbo/gray-matter-ts my-project

CD into my-project and install dependencies:

cd my-project && pnpm install && pnpm build

Then run any of the examples to see how gray-matter works:

node examples/<example_name>

Links to examples

• coffee
• excerpt-separator
• excerpt-stringify
• excerpt
• javascript
• json-stringify
• json
• restore-empty
• sections-excerpt
• sections
• toml
• yaml-stringify
• yaml

API

matter

Takes a string or object with content property, extracts and parses front-matter from the string, then returns an object with data, content and other useful properties.

Params

• input {Object|String}: String, or object with content string
• options {Object}
• returns {Object}

Example

import { matter } from 'gray-matter-ts'

console.log(matter('---\ntitle: Home\n---\nOther stuff'))
// => { data: { title: 'Home'}, content: 'Other stuff' }

stringify

Stringify an object to YAML or the specified language, and append it to the given string. By default, only YAML and JSON can be stringified. See the engines section to learn how to stringify other languages.

Params

• file {String|Object}: The content string to append to stringified front-matter, or a file object with file.content string.
• data {Object}: Front matter to stringify.
• options {Object}: Options to pass to gray-matter and js-yaml.
• returns {String}: Returns a string created by wrapping stringified yaml with delimiters, and appending that to the given string.

Example

import { stringify } from 'gray-matter-ts'
console.log(stringify('foo bar baz', { title: 'Home' }))
// results in:
// ---
// title: Home
// ---
// foo bar baz

read

Synchronously read a file from the file system and parse front matter. Returns the same object as the main function.

Params

• filepath {String}: file path of the file to read.
• options {Object}: Options to pass to gray-matter.
• returns {Object}: Returns an object with data and content

Example

import { read } from 'gray-matter-ts'
const file = read('./content/blog-post.md')

test

Returns true if the given string has front matter.

Params

• str {String}
• options {Object}
• returns {Boolean}: True if front matter exists.

Options

options.excerpt

Type: Boolean|Function

Default: undefined

Extract an excerpt that directly follows front-matter, or is the first thing in the string if no front-matter exists.

If set to excerpt: true, it will look for the frontmatter delimiter, --- by default and grab everything leading up to it.

Example

const str = '---\nfoo: bar\n---\nThis is an excerpt.\n---\nThis is content'
const file = matter(str, { excerpt: true })

Results in:

const file = {
  content: 'This is an excerpt.\n---\nThis is content',
  data: { foo: 'bar' },
  excerpt: 'This is an excerpt.\n'
}

You can also set excerpt to a function. This function uses the 'file' and 'options' that were initially passed to gray-matter as parameters, so you can control how the excerpt is extracted from the content.

Example

// returns the first 4 lines of the contents
function firstFourLines(file, options) {
  file.excerpt = file.content.split('\n').slice(0, 4).join(' ')
}

const file = matter([
  '---',
  'foo: bar',
  '---',
  'Only this',
  'will be',
  'in the',
  'excerpt',
  'but not this...'
].join('\n'), { excerpt: firstFourLines })

Results in:

const file = {
  content: 'Only this\nwill be\nin the\nexcerpt\nbut not this...',
  data: { foo: 'bar' },
  excerpt: 'Only this will be in the excerpt'
}

options.excerpt_separator

Type: String

Default: undefined

Define a custom separator to use for excerpts.

console.log(matter(string, { excerpt_separator: '<!-- end -->' }))

Example

The following HTML string:

---
title: Blog
---
My awesome blog.
<!-- end -->
<h1>Hello world</h1>

Results in:

const file = {
  data: { title: 'Blog' },
  excerpt: 'My awesome blog.',
  content: 'My awesome blog.\n<!-- end -->\n<h1>Hello world</h1>'
}

options.engines

Define custom engines for parsing and/or stringifying front-matter.

Type: Object Object of engines

Default: YAML, JSON are already handled by default.

Engine format

Engines may either be an object with parse and (optionally) stringify methods, or a function that will be used for parsing only.

Examples

import { matter } from 'gray-matter-ts'
import { parse, stringify } from 'smol-toml'

/**
 * defined as a function
 */
const file1 = matter(str, {
  engines: {
    toml: parse,
  }
})

/**
 * Or as an object
 */
const file2 = matter(str, {
  engines: {
    toml: {
      parse,
      stringify,
    }
  }
})

console.log(file1, file2)

You can also use other preset engines we provide, which are not built-in engines and require you to add them manually:

import { matter } from 'gray-matter-ts'

// should install `coffeescript` as a dependency
import { coffee } from 'gray-matter-ts/engines/coffeescript'
import { javascript } from 'gray-matter-ts/engines/javascript'
// should install `smol-toml` as a dependency
import { toml } from 'gray-matter-ts/engines/toml'

const file = matter(str, {
  engines: {
    coffee,
    javascript,
    toml
  }
})

options.language

Type: String

Default: yaml

Define the engine to use for parsing front-matter.

console.log(matter(string, { language: 'toml' }))

Example

The following HTML string:

---
title = "TOML"
description = "Front matter"
categories = "front matter toml"
---
This is content

Results in:

const file = {
  content: 'This is content',
  excerpt: '',
  data:
   { title: 'TOML', description: 'Front matter', categories: 'front matter toml' }
}

Dynamic language detection

Instead of defining the language on the options, gray-matter will automatically detect the language defined after the first delimiter and select the correct engine to use for parsing.

---toml
title = "TOML"
description = "Front matter"
categories = "front matter toml"
---
This is content

options.delimiters

Type: String

Default: ---

Open and close delimiters can be passed in as an array of strings.

Example:

// format delims as a string
read('file.md', { delims: '~~~' })
// or an array (open/close)
read('file.md', { delims: ['~~~', '~~~'] })

would parse:

~~~
title: Home
~~~
This is the {{title}} page.

Deprecated options

options.lang

Decrecated, please use options.language instead.

options.delims

Decrecated, please use options.delimiters instead.

options.parsers

Decrecated, please use options.engines instead.

About

Pull requests and stars are always welcome. For bugs and feature requests, please create an issue.

Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:

pnpm install && pnpm test

License

Released under the MIT License.