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 5.9; 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

For build instructions and contribution guidelines, see docs/CONTRIBUTING.md.

To install:

npm install --save-exact yaml@next
# or
deno add jsr:@eemeli/yaml

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.

Parse & Stringify

As far as possible, these functions work the same as JSON.parse and JSON.stringify.

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

import { parse, stringify } from 'yaml'

parse('[ true, false, maybe, null, 3.14159 ]')
// [ true, false, 'maybe', null, 3.14159 ]

stringify([true, false, 'maybe', null, 3.14159])
// `- true
// - false
// - maybe
// - null
// - 3.14159
// `

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

# 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 'node:fs'
import { parse } from 'yaml'

const file = fs.readFileSync('./file.yml', 'utf8')
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' ] }

Documents

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

import {
  Document,
  parseAllDocuments,
  parseDocument
} from 'yaml'

Content Nodes

• 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)
• visitAsync(node, visitor)

import {
  Scalar,
  visit,
  visitAsync,
  YAMLMap,
  YAMLSeq
} from 'yaml'

Lexer, Concrete Syntax Tree, and AST Composer

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

import { Composer, Lexer, Parser } from 'yaml'

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