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JS-YAML - YAML 1.2 parser and serializer for JavaScript

Build Status

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.


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 js-yaml -g


usage: js-yaml [-h] [-v] [-c] [-j] [-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
  -j, --to-json  Output a non-funky boring JSON
  -t, --trace    Show stack trace on error

Bundled YAML library for browsers

<script src="js-yaml.min.js"></script>
<script type="text/javascript">
var doc = jsyaml.load('greeting: hello\nname: world');

Browser support was done mostly for 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.


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

In node.js JS-YAML automatically registers handlers for .yml and .yaml files. You can load them just with require. That's mostly equivalent to calling load() on fetched content of a file. Just with one string!


// Get document, or throw exception on error
try {
  var doc = require('/home/ixti/example.yml');
} catch (e) {

safeLoad (string [ , options ])

Recommended loading way. Parses string as single YAML document. Returns a JavaScript object or throws YAMLException on error. By default, does not support regexps, functions and undefined. This method is safe for untrusted data.


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, JSON schema is not such strict as defined in the YAML specification. It allows numbers in any notaion, use Null and NULL as null, etc. Core schema also has no such restrictions. It allows binary notation for integers.

load (string [ , options ])

Use with care with untrusted sources. The same as safeLoad() but uses DEFAULT_FULL_SCHEMA by default - adds some JavaScript-specific types: !!js/function, !!js/regexp and !!js/undefined. For untrusted sources you must additionally validate object structure, to avoid injections:

var untrusted_code = '"toString": !<,2002:js/function> "function (){very_evil_thing();}"';

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

safeLoadAll (string, iterator [ , options ])

Same as safeLoad(), but understands multi-document sources and apply iterator to each document.

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

yaml.safeLoadAll(data, function (doc) {

loadAll (string, iterator [ , options ])

Same as safeLoadAll() but uses DEFAULT_FULL_SCHEMA by default.

safeDump (object [ , options ])

Serializes object as YAML document. Uses DEFAULT_SAFE_SCHEMA, so it will throw exception if you try to dump regexps or functions. However, you can disable exceptions by skipInvalid option.


  • indent (default: 2) - indentation width to use (in spaces).
  • 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: DEFAULT_SAFE_SCHEMA) specifies a schema to use.


  "canonical"   => "~"

  "binary"      => "0b1", "0b101010", "0b1110001111010"
  "octal"       => "01", "052", "016172"
  "decimal"     => "1", "42", "7290"
  "hexadecimal" => "0x1", "0x2A", "0x1C7A"

!!null, !!bool, !!float
  "lowercase"   => "null", "true", "false", ".nan", '.inf'
  "uppercase"   => "NULL", "TRUE", "FALSE", ".NAN", '.INF'
  "camelcase"   => "Null", "True", "False", ".NaN", '.Inf'

By default, !!int uses decimal, and !!null, !!bool, !!float use lowercase.

dump (object [ , options ])

Same as safeDump() but without limits (uses DEFAULT_FULL_SCHEMA by default).

Supported YAML types

The list of standard YAML tags and corresponding JavaScipt 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


Note, that you use arrays or objects as key in JS-YAML. JS do not allows objects or array as keys, and stringifies (by calling .toString method) them at the moment of adding them.

? [ 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

Breaking changes in 1.x.x -> 2.0.x

If your have not used custom tags or loader classes - no changes needed. Just upgrade library and enjoy high parse speed.

In other case, you should rewrite your tag constructors and custom loader classes, to conform new schema-based API. See examples and wiki for details. Note, that parser internals were completely rewritten.


View the LICENSE file (MIT).

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