JS-YAML - YAML 1.2 parser / writer for JavaScript

Online Demo

This is an implementation of YAML, a human-friendly data serialization language. Started as PyYAML port, it was completely rewritten from scratch. Now it's very fast, and supports 1.2 spec.

Installation

YAML module for node.js

npm install js-yaml

CLI executable

If you want to inspect your YAML files from CLI, install js-yaml globally:

npm install -g js-yaml

Usage

usage: js-yaml [-h] [-v] [-c] [-t] file

Positional arguments:
  file           File with YAML document(s)
Optional arguments:
  -h, --help     Show this help message and exit.
  -v, --version  Show program's version number and exit.
  -c, --compact  Display errors in compact mode
  -t, --trace    Show stack trace on error

Bundled YAML library for browsers

Browser support was done mostly for the online demo. If you find any errors - feel free to send pull requests with fixes. Also note, that IE and other old browsers needs es5-shims to operate.

Notes:

1. We have no resources to support browserified version. Don't expect it to be well tested. Don't expect fast fixes if something goes wrong there.

2. !!js/function

   in browser bundle will not work by default. If you really need it - load

   esprima

   parser first (via amd or directly).

3. !!bin

   in browser will return

   Array

   , because browsers do not support node.js

   Buffer

   and adding Buffer shims is completely useless on practice.

API

Here we cover the most 'useful' methods. If you need advanced details (creating your own tags), see wiki and examples for more info.

const yaml = require('js-yaml');
const fs   = require('fs');

// Get document, or throw exception on error
try {
  const doc = yaml.safeLoad(fs.readFileSync('/home/ixti/example.yml', 'utf8'));
  console.log(doc);
} catch (e) {
  console.log(e);
}

safeLoad (string [ , options ])

Recommended loading way. Parses

string

null

undefined

YAMLException

options:

• filename

  (default: null) - string to be used as a file path in error/warning messages.

• onWarning

  (default: null) - function to call on warning messages. Loader will call this function with an instance of

  YAMLException

  for each warning.

• schema

  (default: `DEFAULTSAFESCHEMA`) - specifies a schema to use.

  • FAILSAFE_SCHEMA

    - only strings, arrays and plain objects: http://www.yaml.org/spec/1.2/spec.html#id2802346

  • JSON_SCHEMA

    - all JSON-supported types: http://www.yaml.org/spec/1.2/spec.html#id2803231

  • CORE_SCHEMA

    - same as

    JSON_SCHEMA

    : http://www.yaml.org/spec/1.2/spec.html#id2804923

  • DEFAULT_SAFE_SCHEMA

    - all supported YAML types, without unsafe ones (

    !!js/undefined

    ,

    !!js/regexp

    and

    !!js/function

    ): http://yaml.org/type/

  • DEFAULT_FULL_SCHEMA

    - all supported YAML types.

• json

  (default: false) - compatibility with JSON.parse behaviour. If true, then duplicate keys in a mapping will override values rather than throwing an error.

NOTE: This function does not understand multi-document sources, it throws exception on those.

NOTE: JS-YAML does not support schema-specific tag resolution restrictions. So, the JSON schema is not as strictly defined in the YAML specification. It allows numbers in any notation, use

Null

NULL

null

load (string [ , options ])

Use with care with untrusted sources. The same as

safeLoad()

DEFAULT_FULL_SCHEMA

!!js/function

!!js/regexp

!!js/undefined

const untrusted_code = '"toString": ! "function (){very_evil_thing();}"';

// I'm just converting that string, what could possibly go wrong?
require('js-yaml').load(untrusted_code) + ''
</yaml.org>

safeLoadAll (string [, iterator] [, options ])

Same as

safeLoad()

iterator

const yaml = require('js-yaml');

yaml.safeLoadAll(data, function (doc) {
  console.log(doc);
});

loadAll (string [, iterator] [ , options ])

Same as

safeLoadAll()

DEFAULT_FULL_SCHEMA

safeDump (object [ , options ])

Serializes

object

DEFAULT_SAFE_SCHEMA

skipInvalid

true

options:

• indent

  (default: 2) - indentation width to use (in spaces).

• noArrayIndent

  (default: false) - when true, will not add an indentation level to array elements

• skipInvalid

  (default: false) - do not throw on invalid types (like function in the safe schema) and skip pairs and single values with such types.

• flowLevel

  (default: -1) - specifies level of nesting, when to switch from block to flow style for collections. -1 means block style everwhere

• styles

  - "tag" => "style" map. Each tag may have own set of styles.

• schema

  (default: `DEFAULTSAFESCHEMA`) specifies a schema to use.

• sortKeys

  (default:

  false

  ) - if

  true

  , sort keys when dumping YAML. If a function, use the function to sort the keys.

• lineWidth

  (default:

  80

  ) - set max line width.

• noRefs

  (default:

  false

  ) - if

  true

  , don't convert duplicate objects into references

• noCompatMode

  (default:

  false

  ) - if

  true

  don't try to be compatible with older yaml versions. Currently: don't quote "yes", "no" and so on, as required for YAML 1.1

• condenseFlow

  (default:

  false

  ) - if

  true

  flow sequences will be condensed, omitting the space between

  a, b

  . Eg.

  '[a,b]'

  , and omitting the space between

  key: value

  and quoting the key. Eg.

  '{"a":b}'

  Can be useful when using yaml for pretty URL query params as spaces are %-encoded.

The following table show availlable styles (e.g. "canonical", "binary"...) available for each tag (.e.g. !!null, !!int ...). Yaml output is shown on the right side after

=>

->

!!null
  "canonical"   -> "~"
  "lowercase"   => "null"
  "uppercase"   -> "NULL"
  "camelcase"   -> "Null"

!!int
  "binary"      -> "0b1", "0b101010", "0b1110001111010"
  "octal"       -> "01", "052", "016172"
  "decimal"     => "1", "42", "7290"
  "hexadecimal" -> "0x1", "0x2A", "0x1C7A"
!!bool
  "lowercase"   => "true", "false"
  "uppercase"   -> "TRUE", "FALSE"
  "camelcase"   -> "True", "False"
!!float
  "lowercase"   => ".nan", '.inf'
  "uppercase"   -> ".NAN", '.INF'
  "camelcase"   -> ".NaN", '.Inf'

Example:

safeDump (object, {
  'styles': {
    '!!null': 'canonical' // dump null as ~
  },
  'sortKeys': true        // sort object keys
});

dump (object [ , options ])

Same as

safeDump()

DEFAULT_FULL_SCHEMA

Supported YAML types

The list of standard YAML tags and corresponding JavaScript types. See also YAML tag discussion and YAML types repository.

!!null ''                   # null
!!bool 'yes'                # bool
!!int '3...'                # number
!!float '3.14...'           # number
!!binary '...base64...'     # buffer
!!timestamp 'YYYY-...'      # date
!!omap [ ... ]              # array of key-value pairs
!!pairs [ ... ]             # array or array pairs
!!set { ... }               # array of objects with given keys and null values
!!str '...'                 # string
!!seq [ ... ]               # array
!!map { ... }               # object

JavaScript-specific tags

!!js/regexp /pattern/gim            # RegExp
!!js/undefined ''                   # Undefined
!!js/function 'function () {...}'   # Function

Caveats

Note, that you use arrays or objects as key in JS-YAML. JS does not allow objects or arrays as keys, and stringifies (by calling

toString()

---
? [ foo, bar ]
: - baz
? { foo: bar }
: - baz
  - baz

{ "foo,bar": ["baz"], "[object Object]": ["baz", "baz"] }

Also, reading of properties on implicit block mapping keys is not supported yet. So, the following YAML document cannot be loaded.

&anchor foo:
  foo: bar
  *anchor: duplicate key
  baz: bat
  *anchor: duplicate key

js-yaml for enterprise

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