gray-matter

What is gray-matter?

The gray-matter npm package is used to parse front-matter from strings or files. Front-matter is metadata stored at the top of a file, typically in YAML or JSON format, which is often used in static site generators and other content management systems.

What are gray-matter's main functionalities?

Parsing Front-Matter

This feature allows you to parse front-matter from a string. The front-matter is typically written in YAML or JSON format and is separated from the content by triple dashes (---). The parsed object contains the metadata and the content separately.

const matter = require('gray-matter');
const file = '---\ntitle: Hello World\ndate: 2023-10-01\n---\nThis is the content of the file.';
const parsed = matter(file);
console.log(parsed);

Stringify Front-Matter

This feature allows you to convert a content string and a metadata object back into a string with front-matter. This is useful for generating files with front-matter programmatically.

const matter = require('gray-matter');
const data = { title: 'Hello World', date: '2023-10-01' };
const content = 'This is the content of the file.';
const stringified = matter.stringify(content, data);
console.log(stringified);

Custom Delimiters

This feature allows you to specify custom delimiters for the front-matter. By default, gray-matter uses triple dashes (---), but you can change this to any string you prefer.

const matter = require('gray-matter');
const file = '+++\ntitle = "Hello World"\ndate = "2023-10-01"\n+++\nThis is the content of the file.';
const parsed = matter(file, { delimiters: '+++' });
console.log(parsed);

Other packages similar to gray-matter

front-matter

The front-matter package is another tool for parsing front-matter from strings. It is simpler and has fewer features compared to gray-matter, but it is also lightweight and easy to use.

js-yaml

The js-yaml package is primarily used for parsing and stringifying YAML, but it can also be used to handle front-matter. It is more general-purpose and powerful for YAML processing, but it requires more setup to use for front-matter specifically.

marked

The marked package is a markdown parser that can also handle front-matter if used in conjunction with other tools. It is more focused on converting markdown to HTML, but it can be extended to support front-matter parsing.

README

gray-matter

A simple to use and extend front matter library. Supports parsing and extracting YAML, JSON, TOML or Coffee Front-Matter, with options to set custom delimiters.

Used by assemble, verb, and thousands of other projects!

v0.5.0 has breaking changes!

• YAML is now parsed using the .safeLoad() method from js-yaml.
• To parse coffee, CSON or javascript front matter, you must set options.eval to true.
• stringify() has been renamed to toJSON()
• stringifyYAML() has been renamed to toYAML()

Highlights

• Reliable and battle-tested.
• Will extract and parse:
  • YAML
  • JSON
  • TOML
  • CoffeeScript when options.eval is set to true
  • CSON when options.eval is set to true
  • JavaScript: when options.eval is set to true
• Easy to add additional parsers! pull requests welcome!

TOC

• Highlights
• Install
• Usage
• API
  • [matter](#matterindexjsl47)
  • [.read](#readindexjsl111)
  • [.exists](#existsindexjsl134)
  • [.extend](#extendindexjsl154)
  • [.reconstruct](#reconstructindexjsl179)
  • [.toJSON](#tojsonindexjsl194)
  • [.toYAML](#toyamlindexjsl207)
• Options
  • options.eval
  • options.lang
  • options.delims
  • options.autodetect
• Examples
  • .extend
• Why?
• Authors
• License

Install

Install with npm

npm i gray-matter --save

Install with bower

bower install gray-matter --save

Usage

var matter = require('gray-matter');
console.log(matter('---\ntitle: foo\n---\nbar');
//=> {data: {title: 'foo'}, content: 'bar', orig: '---\ntitle: foo\n---\nbar'}

API

matter

Expects a string and returns and object:

• str {String}: The string to parse
• options {Object}: Object of options
• returns {Object} file: Object with the following properties.

matter('---\ntitle: Blog\n---\nThis is content.');

Returns:

{
  "data": {"title": "Blog"},
  "content": "This is content.",
  "original": "---\ntitle: Blog\n---\nThis is content."
}

.read

Read a file then pass the string and options to matter() for parsing:

• filepath {String}
• options {Object}
• returns {Object} file: Same object as matter(), with an additional path property

matter.read('file.md');

Returns something like:

{
  "data": {"title": "Blog"},
  "content": "This is content.",
  "original": "---\ntitle: Blog\n---\nThis is content."
}

.exists

Return true if front-matter exists.

• str {String}: The string to parse
• options {Object}: Options to pass to matter()
• returns {Boolean} true: or false

matter.exists(str);

.extend

Extend and stringify YAML front matter. Takes an object as the second parameter, and returns either the extended, stringified object (YAML), or if no front matter is found an empty string is returned.

• str {String}: The string to parse
• obj {Object}: The object to use to extend the front matter.
• returns {String}: String with extended YAML front matter.

matter.extend(str, obj);

.reconstruct

A convenience wrapper around the matter() and matter.extend() methods.

• str {String}: The string to parse
• obj {Object}: The object to use to extend the front matter.
• returns {String}: Original string with extended front matter.

Extends YAML front matter, then re-assembles front matter with the content of the file.

matter.reconstruct(str, obj);

.toJSON

• str {String}
• options {Object}
• returns {Object}: Parsed front matter as JSON.

Convenience wrapper around the matter(str).data() method.

.toYAML

• str {String}
• options {Object}
• returns {String}: Stringified YAML.

Stringify parsed front matter back to YAML.

Options

All methods will accept an options object to be passed as a second parameter

options.eval

Type: Boolean

Default: false

Evaluate coffee-script, CSON or JavaScript in front-matter. If you aren't aware of the dangers, google is your friend.

options.lang

Type: String

Default: yaml

The parser to use on the extracted front matter. Valid options include:

• yaml
• json
• coffee
• cson
• toml
• js|javascript

options.delims

Type: Object

Default: {delims: ['---', '---']}

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

matter.read('file.md', {delims: ['~~~', '~~~']});

You may also pass an array of arrays, allowing multiple alternate delimiters to be used. Example:

{
  delims: [
    ['---', '~~~'], ['---', '~~~']
  ]
}

Note that passing multiple delimiters will yield unpredictable results, it is recommended that you use this option only for testing purposes.

options.autodetect

Type: Boolean

Default: undefined

Attempts to automatically register a language that is specified after the first code boundary (delimiter).

Usage Example:

--- coffee
user = 'jonschlinkert'
reverse = (src) ->
  src.split('').reverse().join('')
---

{%= user %}
{%= reverse(user) %}

Examples

Let's say our page, foo.html contains

---
title: YAML Front matter
description: This is a page
---
<h1>{{title}}</h1>

then running the following in the command line:

console.log(matter('foo.html'));

returns

{
  "data": {
    "title": "YAML Front matter",
    "description": "This is a page"
  },
  "content": "<h1>{{title}}</h1>",
  "original": "---\ntitle: YAML Front matter\n---\n<h1>{{title}}</h1>"
}

and

console.log(matter('foo.html').data);

returns

{"title": "YAML Front matter", "description": "This is a page"}

.extend

Given this page:

---
title: Gray Matter
---
Hooray!

and this config:

var file = require('fs').readFileSync('file.md', 'utf8');
var obj = {
  description: 'A simple to use front matter lib';
};
matter.extend(file, obj);

the result would be:

---
title: Gray Matter
description: A simple to use front matter lib
---
Hooray!

Why?

Why another YAML Front Matter library?

Because other libraries we tried failed to meet our requirements with Assemble. Some most of the libraries met most of the requirements, but none had all of them. Here are the most important:

• Be usable, if not simple
• Allow custom delimiters
• Use a dependable and well-supported library for parsing YAML and other languages
• Don't fail when no content exists
• Don't fail when no front matter exists
• Have no problem reading YAML files directly
• Have no problem with complex content, including fenced code blocks that contain examples of YAML front matter. Other parsers fail on this.
• Should return an object that contains the parsed YAML front matter and content, as well as the "original" content.

Authors

Jon Schlinkert

• github/assemble
• twitter/assemble

License

Copyright (c) 2014 Jon Schlinkert, contributors.
Released under the MIT license

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This file was generated by verb-cli on September 24, 2014.