js-yaml vs yaml vs yamljs
YAML Parsing and Stringifying Comparison
1 Year
js-yamlyamlyamljsSimilar Packages:
What's YAML Parsing and Stringifying?

YAML (YAML Ain't Markup Language) is a human-readable data serialization format often used for configuration files, data exchange, and more. In JavaScript, libraries like js-yaml, yaml, and yamljs provide tools for parsing YAML files into JavaScript objects and stringifying objects back into YAML format. These libraries are essential for applications that need to read from or write to YAML files, offering features like support for complex data types, custom serialization, and more. js-yaml is a widely-used library known for its simplicity and performance, while yaml offers a modern API with advanced features like streaming and custom tags. yamljs, on the other hand, focuses on ease of use and provides a straightforward interface for working with YAML in JavaScript.

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js-yaml111,609,7526,414-674 years agoMIT
yaml66,597,9101,454683 kB2017 days agoISC
yamljs1,989,023891-538 years agoMIT
Feature Comparison: js-yaml vs yaml vs yamljs

Parsing and Stringifying

  • js-yaml:

    js-yaml provides efficient parsing and stringifying of YAML, supporting complex data structures, custom tags, and error handling. It is known for its reliability and performance, making it suitable for a wide range of applications.

  • yaml:

    yaml offers advanced parsing and stringifying capabilities with support for streaming, custom tags, and more. It is designed for performance and flexibility, allowing for better handling of large YAML files and complex data types.

  • yamljs:

    yamljs offers basic parsing and stringifying of YAML with a focus on simplicity. It supports standard YAML features but lacks some of the advanced capabilities found in js-yaml and yaml, making it more suitable for straightforward use cases.

Streaming Support

  • js-yaml:

    js-yaml does not natively support streaming for parsing or stringifying YAML. It processes the entire input at once, which can be a limitation for very large YAML files.

  • yaml:

    yaml provides built-in streaming support for both parsing and stringifying, allowing for more efficient handling of large YAML files. This feature reduces memory consumption and improves performance when working with extensive data.

  • yamljs:

    yamljs does not support streaming. It reads and writes YAML data in a single operation, which may lead to high memory usage with large files.

Custom Tags

  • js-yaml:

    js-yaml supports custom tags, allowing developers to define their own data types and serialization methods. This feature provides flexibility for handling non-standard YAML structures.

  • yaml:

    yaml also supports custom tags and offers more advanced features, including better handling of tag resolution and serialization. It allows for more complex and flexible implementations of custom data types.

  • yamljs:

    yamljs supports custom tags but with limited functionality compared to js-yaml and yaml. It allows for basic customization of how certain data types are handled during parsing and stringifying.

Error Handling

  • js-yaml:

    js-yaml provides basic error handling for parsing and stringifying operations, including informative error messages for syntax errors and invalid data.

  • yaml:

    yaml offers more robust error handling, including support for asynchronous parsing and detailed error reporting. It is designed to handle errors more gracefully, especially in complex YAML structures.

  • yamljs:

    yamljs provides simple error handling for parsing errors but is less comprehensive than js-yaml and yaml. It may not provide detailed error messages for all types of parsing issues.

Ease of Use: Code Examples

  • js-yaml:

    js-yaml Example

    const yaml = require('js-yaml');
    const fs = require('fs');
    
    // Parse YAML
    const doc = yaml.load(fs.readFileSync('file.yaml', 'utf8'));
    console.log(doc);
    
    // Stringify YAML
    const yamlStr = yaml.dump(doc);
    console.log(yamlStr);
    
  • yaml:

    yaml Example

    const { parse, stringify } = require('yaml');
    const fs = require('fs');
    
    // Parse YAML
    const doc = parse(fs.readFileSync('file.yaml', 'utf8'));
    console.log(doc);
    
    // Stringify YAML
    const yamlStr = stringify(doc);
    console.log(yamlStr);
    
  • yamljs:

    yamljs Example

    const YAML = require('yamljs');
    
    // Parse YAML
    const doc = YAML.load('file.yaml');
    console.log(doc);
    
    // Stringify YAML
    const yamlStr = YAML.stringify(doc);
    console.log(yamlStr);
    
How to Choose: js-yaml vs yaml vs yamljs
  • js-yaml:

    Choose js-yaml if you need a reliable, well-established library for parsing and dumping YAML with good performance and compatibility. It is suitable for most use cases and has a simple API.

  • yaml:

    Choose yaml if you want a modern, feature-rich library that supports advanced YAML features, streaming, and custom serialization. It is ideal for projects that require more flexibility and performance optimizations.

  • yamljs:

    Choose yamljs if you prefer a lightweight library with a simple API for quick YAML parsing and stringifying tasks. It is great for smaller projects or when you need a straightforward solution without many dependencies.

README for js-yaml

JS-YAML - YAML 1.2 parser / writer for JavaScript

CI NPM version

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

API

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

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

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

load (string [ , options ])

Parses string as single YAML document. Returns either a plain object, a string, a number, null or undefined, or throws YAMLException on error. By default, does not support regexps, functions and undefined.

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_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_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.

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

Same as load(), but understands multi-document sources. Applies iterator to each document if specified, or returns array of documents.

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

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

dump (object [ , options ])

Serializes object as a YAML document. Uses DEFAULT_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_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. Set -1 for unlimited 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.
  • quotingType (' or ", default: ') - strings will be quoted using this quoting style. If you specify single quotes, double quotes will still be used for non-printable characters.
  • forceQuotes (default: false) - if true, all non-key strings will be quoted even if they normally don't need to.
  • replacer - callback function (key, value) called recursively on each key/value in source object (see replacer docs for JSON.stringify).

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"       -> "0o1", "0o52", "0o16172"
  "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:

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

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

See js-yaml-js-types for extra types.

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

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