Yaml Front Matter

Parses yaml or json at the front of a string. Places the parsed content, plus the rest of the string content, into an object literal.

Online Demo.

Breaking Changes

This readme is for the 4.x branch which introduces breaking changes. View the changelog for more information.

3.x readme

Example

This

---
name: Derek Worthen
age: 127
contact:
  email: email@domain.com
  address: some location
pets:
  - cat
  - dog
  - bat
match: !!js/regexp /pattern/gim
run: !!js/function function() { }
---
Some Other content

var fs = require('fs');
var yamlFront = require('yaml-front-matter');
 
fs.readFile('./some/file.txt', 'utf8', function(fileContents) {
    console.log(yamlFront.loadFront(fileContents));
});
 

outputs

{ 
    name: 'Derek Worthen',
    age: 127,
    contact: { email: 'email@domain.com', address: 'some location' },
    pets: [ 'cat', 'dog', 'bat' ],
    match: /pattern/gim,
    run: [Function],
    __content: '\nSome Other Content' 
}

May also use JSON

---
{
    "name": "Derek Worthen",
    "age": "young",
    "anArray": ["one","two"],
    "subObj":{"field1": "one"}
}
---
Some content

NOTE: The --- are required to denote the start and end of front matter. There must be a newline after the opening --- and a newline preceding the closing ---.

Install

npm

$ npm install yaml-front-matter

Use the -g flag if you plan on using the command line tool.

$ npm install yaml-front-matter -g

Node or client with module bundler (webpack or browsify)

var yamlFront = require('yaml-front-matter');

Browser Bundle

The dist/yamlFront.js client script will expose the yaml-front-matter library as a global, yamlFront. The client script for js-yaml is also required. May need to load espirma for some use cases. See js-yaml for more information.

<script src="https://unpkg.com/js-yaml@3.10.0/dist/js-yaml.js"></script>
<script src="yamlFront.js"></script>
<script>
  // parse front matter with yamlFront.loadFront(String);
</script> 

Note: yaml-front-matter is delivered as a umd package so it should work within commonjs, amd and browser (as a global) environments.

Running Browser Example

$ npm install --dev && npm start

Then visit localhost:8080.

Building from source

Outputs build files to dist/.

$ npm install --dev && npm run build

Running Tests

npm install --dev && npm test

Command Line

Usage: yaml-front-matter [options] <yaml-front-matter content>
 
Options:
 
-h, --help            output usage information
-v, --version         output the version number
-c, --content [name]  set the property name for the files contents [__content]
--pretty              formats json output with spaces. 

Note The cli uses safeLoadFront and therefore will not parse yaml containing regexps, functions or undefined values.

Example

# Piping content from one file, through yaml parser and into another file 
cat ./some/file.txt | yaml-front-matter > output.txt

JS-YAML

Yaml front matter wraps js-yaml to support parsing yaml front-matter.

API

loadFront(string, [options])

var input = [
        '---\npost: title one\n',
        'anArray:\n - one\n - two\n',
        'subObject:\n prop1: cool\n prop2: two',
        '\nreg: !!js/regexp /pattern/gim',
        '\nfun: !!js/function function() {  }\n---\n',
        'content\nmore'
    ].join('');
 
var results = yamlFront.loadFront(input);
console.log(results);

outputs

{ post: 'title one',
  anArray: [ 'one', 'two' ],
  subObject: { obj1: 'cool', obj2: 'two' },
  reg: /pattern/gim,
  fun: [Function],
  __content: '\ncontent\nmore' }

Front-matter is optional.

yamlFront.loadFront('Hello World');
// => { __content: "Hello World!" }

Content is optional

yamlFront.loadFront('');
// => { __content: '' }

safeLoadFront(string, [options])

Same api as loadFront except it does not support regexps, functions or undefined. See js-yaml for more information.

Options

The options object supports the same options available to js-yaml and adds support for an additional key.

• options.contentKeyName: Specify the object key where to store content not parsed by yaml-front-matter. defaults to __content.

yamlFront.loadFront('Hello World', {
    contentKeyName: 'fileContents' 
});
// => { fileContents: "Hello World" }