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

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

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` as single YAML document. Returns either a plain object, a string or `undefined`, or throws `YAMLException` on error. By default, does not support regexps, functions and undefined. This method is safe for untrusted data.

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: `DEFAULT_SAFE_SCHEMA`)_ - 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` and `NULL` as `null`, etc. The 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:

const untrusted_code = '"toString": !<tag:yaml.org,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. Applies `iterator` to each document if specified, or returns array of documents.

const yaml = require('js-yaml');
yaml.safeLoadAll(data, function (doc) {
console.log(doc);
});

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

Same as `safeLoadAll()` but uses `DEFAULT_FULL_SCHEMA` by default.

## safeDump (object [ , options ])

Serializes `object` as a YAML document. Uses `DEFAULT_SAFE_SCHEMA`, so it will throw an exception if you try to dump regexps or functions. However, you can disable exceptions by setting the `skipInvalid` option to `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: `DEFAULT_SAFE_SCHEMA`)_ 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 `=>` (default setting) or `->`:

!!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()` 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

# 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()` 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

# js-yaml for enterprise

Available as part of the Tidelift Subscription

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