yaml

What is yaml?

The 'yaml' npm package is a JavaScript library for parsing and serializing YAML, a human-friendly data serialization standard. It can be used to convert YAML to JSON and vice versa, and to work with YAML content programmatically in JavaScript.

What are yaml's main functionalities?

Parsing YAML to JSON

This feature allows you to parse a string of YAML content and convert it into a JavaScript object.

const yaml = require('yaml');
const yamlText = 'key: value\nnumber: 123';
const jsonObject = yaml.parse(yamlText);
console.log(jsonObject);

Stringifying JSON to YAML

This feature enables you to take a JavaScript object and serialize it into a YAML formatted string.

const yaml = require('yaml');
const jsonObject = { key: 'value', number: 123 };
const yamlText = yaml.stringify(jsonObject);
console.log(yamlText);

Custom Tags

This feature allows you to define custom tags for specialized YAML types, enabling the parsing of YAML content with custom data structures.

const yaml = require('yaml');
const customType = { identify: value => value instanceof Set, tag: 'tag:yaml.org,2002:set', resolve: (doc, cst) => new Set(cst.strValue.split(', ')) };
yaml.defaultOptions.customTags = [customType];
const yamlText = '!!set a, b, c';
const data = yaml.parse(yamlText);
console.log(data);

Other packages similar to yaml

js-yaml

js-yaml is another popular YAML parser and serializer for JavaScript. It offers similar functionality to the 'yaml' package, including parsing and stringifying, and it also provides a safe loading option to prevent executing arbitrary code during parsing.

yamljs

yamljs is a YAML parser and dumper written in JavaScript. It provides functionality similar to 'yaml' and 'js-yaml' but has a different API design and may have different performance characteristics.

README

YAML

yaml is a definitive library for YAML, the human friendly data serialization standard. This library:

• Supports both YAML 1.1 and YAML 1.2 and all common data schemas,
• Passes all of the yaml-test-suite tests,
• Can accept any string as input without throwing, parsing as much YAML out of it as it can, and
• Supports parsing, modifying, and writing YAML comments and blank lines.

The library is released under the ISC open source license, and the code is available on GitHub. It has no external dependencies and runs on Node.js as well as modern browsers.

For the purposes of versioning, any changes that break any of the documented endpoints or APIs will be considered semver-major breaking changes. Undocumented library internals may change between minor versions, and previous APIs may be deprecated (but not removed).

The minimum supported TypeScript version of the included typings is 3.9; for use in earlier versions you may need to set skipLibCheck: true in your config. This requirement may be updated between minor versions of the library.

For more information, see the project's documentation site: eemeli.org/yaml

To install:

npm install yaml

Note: These docs are for yaml@2. For v1, see the v1.10.0 tag for the source and eemeli.org/yaml/v1 for the documentation.

The development and maintenance of this library is sponsored by:

API Overview

The API provided by yaml has three layers, depending on how deep you need to go: Parse & Stringify, Documents, and the underlying Lexer/Parser/Composer. The first has the simplest API and "just works", the second gets you all the bells and whistles supported by the library along with a decent AST, and the third lets you get progressively closer to YAML source, if that's your thing.

A command-line tool is also included.

import { parse, stringify } from 'yaml'
// or
import YAML from 'yaml'
// or
const YAML = require('yaml')

Parse & Stringify

• parse(str, reviver?, options?): value
• stringify(value, replacer?, options?): string

Documents

• Document
  • constructor(value, replacer?, options?)
  • #anchors
  • #contents
  • #directives
  • #errors
  • #warnings
• isDocument(foo): boolean
• parseAllDocuments(str, options?): Document[]
• parseDocument(str, options?): Document

Content Nodes

• isAlias(foo): boolean
• isCollection(foo): boolean
• isMap(foo): boolean
• isNode(foo): boolean
• isPair(foo): boolean
• isScalar(foo): boolean
• isSeq(foo): boolean
• new Scalar(value)
• new YAMLMap()
• new YAMLSeq()
• doc.createAlias(node, name?): Alias
• doc.createNode(value, options?): Node
• doc.createPair(key, value): Pair
• visit(node, visitor)

Parsing YAML

• new Lexer().lex(src)
• new Parser(onNewLine?).parse(src)
• new Composer(options?).compose(tokens)

YAML.parse

# file.yml
YAML:
  - A human-readable data serialization language
  - https://en.wikipedia.org/wiki/YAML
yaml:
  - A complete JavaScript implementation
  - https://www.npmjs.com/package/yaml

import fs from 'fs'
import YAML from 'yaml'

YAML.parse('3.14159')
// 3.14159

YAML.parse('[ true, false, maybe, null ]\n')
// [ true, false, 'maybe', null ]

const file = fs.readFileSync('./file.yml', 'utf8')
YAML.parse(file)
// { YAML:
//   [ 'A human-readable data serialization language',
//     'https://en.wikipedia.org/wiki/YAML' ],
//   yaml:
//   [ 'A complete JavaScript implementation',
//     'https://www.npmjs.com/package/yaml' ] }

YAML.stringify

import YAML from 'yaml'

YAML.stringify(3.14159)
// '3.14159\n'

YAML.stringify([true, false, 'maybe', null])
// `- true
// - false
// - maybe
// - null
// `

YAML.stringify({ number: 3, plain: 'string', block: 'two\nlines\n' })
// `number: 3
// plain: string
// block: |
//   two
//   lines
// `

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