Installation

# Preserve existing imports with an npm alias
npm install json5@npm:@stackline/json5@1.0.0
# Or use the scoped package name in your imports
npm install @stackline/json5@1.0.0

Node.js: >=6. Read the compatibility and maintenance notes before migrating.

Usage and API

The reference below may retain upstream package names. Use the alias installation above to run those imports with this Stackline release.

JSON5 – JSON for Humans

JSON5 is an extension to the popular JSON file format that aims to be easier to write and maintain by hand (e.g. for config files). It is not intended to be used for machine-to-machine communication. (Keep using JSON or other file formats for that. 🙂)

JSON5 was started in 2012, and as of 2022, now gets >65M downloads/week, ranks in the top 0.1% of the most depended-upon packages on npm, and has been adopted by major projects like Chromium, Next.js, Babel, Retool, WebStorm, and more. It's also natively supported on Apple platforms like MacOS and iOS.

Formally, the JSON5 Data Interchange Format is a superset of JSON (so valid JSON files will always be valid JSON5 files) that expands its syntax to include some productions from ECMAScript 5.1 (ES5). It's also a strict subset of ES5, so valid JSON5 files will always be valid ES5.

This JavaScript library is a reference implementation for JSON5 parsing and serialization, and is directly used in many of the popular projects mentioned above (where e.g. extreme performance isn't necessary), but others have created many other libraries across many other platforms.

Summary of Features

The following ECMAScript 5.1 features, which are not supported in JSON, have been extended to JSON5.

Objects

• Object keys may be an ECMAScript 5.1 IdentifierName.
• Objects may have a single trailing comma.

Arrays

• Arrays may have a single trailing comma.

Strings

• Strings may be single quoted.
• Strings may span multiple lines by escaping new line characters.
• Strings may include character escapes.

Numbers

• Numbers may be hexadecimal.
• Numbers may have a leading or trailing decimal point.
• Numbers may be IEEE 754 positive infinity, negative infinity, and NaN.
• Numbers may begin with an explicit plus sign.

Comments

• Single and multi-line comments are allowed.

White Space

• Additional white space characters are allowed.

Example

Kitchen-sink example:

{
  // comments
  unquoted: 'and you can quote me on that',
  singleQuotes: 'I can use "double quotes" here',
  lineBreaks: "Look, Mom! \
No \\n's!",
  hexadecimal: 0xdecaf,
  leadingDecimalPoint: .8675309, andTrailing: 8675309.,
  positiveSign: +1,
  trailingComma: 'in objects', andIn: ['arrays',],
  "backwardsCompatible": "with JSON",
}

A more real-world example is this config file from the Chromium/Blink project.

Specification

For a detailed explanation of the JSON5 format, please read the official specification.

Installation and Usage

Node.js

npm install json5

CommonJS

const JSON5 = require('json5')

Modules

import JSON5 from 'json5'

Browsers

UMD

<!-- This will create a global `JSON5` variable. -->
<script src="https://unpkg.com/json5@2/dist/index.min.js"></script>

Modules

<script type="module">
  import JSON5 from 'https://unpkg.com/json5@2/dist/index.min.mjs'
</script>

API

The JSON5 API is compatible with the JSON API.

JSON5.parse()

Parses a JSON5 string, constructing the JavaScript value or object described by the string. An optional reviver function can be provided to perform a transformation on the resulting object before it is returned.

Syntax

JSON5.parse(text[, reviver])

Parameters

• text: The string to parse as JSON5.
• reviver: If a function, this prescribes how the value originally produced by parsing is transformed, before being returned.

Return value

The object corresponding to the given JSON5 text.

JSON5.stringify()

Converts a JavaScript value to a JSON5 string, optionally replacing values if a replacer function is specified, or optionally including only the specified properties if a replacer array is specified.

Syntax

JSON5.stringify(value[, replacer[, space]])
JSON5.stringify(value[, options])

Parameters

• value: The value to convert to a JSON5 string.
• replacer: A function that alters the behavior of the stringification process, or an array of String and Number objects that serve as a whitelist for selecting/filtering the properties of the value object to be included in the JSON5 string. If this value is null or not provided, all properties of the object are included in the resulting JSON5 string.
• space: A String or Number object that's used to insert white space into the output JSON5 string for readability purposes. If this is a Number, it indicates the number of space characters to use as white space; this number is capped at 10 (if it is greater, the value is just 10). Values less than 1 indicate that no space should be used. If this is a String, the string (or the first 10 characters of the string, if it's longer than that) is used as white space. If this parameter is not provided (or is null), no white space is used. If white space is used, trailing commas will be used in objects and arrays.
• options: An object with the following properties:
  • replacer: Same as the replacer parameter.
  • space: Same as the space parameter.
  • quote: A String representing the quote character to use when serializing strings.

Return value

A JSON5 string representing the value.

Node.js require() JSON5 files

When using Node.js, you can require() JSON5 files by adding the following statement.

require('json5/lib/register')

Then you can load a JSON5 file with a Node.js require() statement. For example:

const config = require('./config.json5')

CLI

Since JSON is more widely used than JSON5, this package includes a CLI for converting JSON5 to JSON and for validating the syntax of JSON5 documents.

Installation

npm install --global json5

Usage

json5 [options] <file>

If <file> is not provided, then STDIN is used.

Options:

• -s, --space: The number of spaces to indent or t for tabs
• -o, --out-file [file]: Output to the specified file, otherwise STDOUT
• -v, --validate: Validate JSON5 but do not output JSON
• -V, --version: Output the version number
• -h, --help: Output usage information

Contributing

Development

git clone https://github.com/json5/json5
cd json5
npm install

When contributing code, please write relevant tests and run npm test and npm run lint before submitting pull requests. Please use an editor that supports EditorConfig.

Issues

To report bugs or request features regarding the JSON5 data format, please submit an issue to the official specification repository.

Note that we will never add any features that make JSON5 incompatible with ES5; that compatibility is a fundamental premise of JSON5.

To report bugs or request features regarding this JavaScript implementation of JSON5, please submit an issue to this repository.

Security Vulnerabilities and Disclosures

To report a security vulnerability, please follow the follow the guidelines described in our security policy.

License

MIT. See LICENSE.md for details.

Credits

Aseem Kishore founded this project. He wrote a blog post about the journey and lessons learned 10 years in.

Michael Bolin independently arrived at and published some of these same ideas with awesome explanations and detail. Recommended reading: Suggested Improvements to JSON

Douglas Crockford of course designed and built JSON, but his state machine diagrams on the JSON website, as cheesy as it may sound, gave us motivation and confidence that building a new parser to implement these ideas was within reach! The original implementation of JSON5 was also modeled directly off of Doug’s open-source json_parse.js parser. We’re grateful for that clean and well-documented code.

Max Nanasy has been an early and prolific supporter, contributing multiple patches and ideas.

Andrew Eisenberg contributed the original stringify method.

Jordan Tucker has aligned JSON5 more closely with ES5, wrote the official JSON5 specification, completely rewrote the codebase from the ground up, and is actively maintaining this project.

Upstream issues and maintenance review

Upstream origin and triage

• Original package: json5@2.2.3
• Repository: https://github.com/json5/json5
• Source commit: https://github.com/json5/json5/commit/c3a75242772a5026a49c4017a16d9b3543b62776
• Source directory: .
• npm tarball: https://registry.npmjs.org/json5/-/json5-2.2.3.tgz
• SHA512 integrity: sha512-XmOWe7eyHYH14cLdVPoyg+GOH3rYX++KpzrylJwSW98t3Nk+U8XOl8FWKOgwtzdb8lXGf6zYwDUzeHMWfxasyg==
• npm last-release age selects maintenance scope; it does not imply no ongoing source development.

Reviewed issues

Primary-source snapshot: 2026-09-29T00:21:55.836825+00:00. Most recently updated 100 open and 30 closed issue/PR entries; PRs removed. This is triage evidence, not a claim of exhaustive review.

Maintenance adoption with preserved runtime payload. No runtime defect correction is claimed. Reports remain visible for subsequent targeted reproduction.

• 348: migrate to ESModules
• 192: Handling invalid unicode escapes
• 292: Support Integers outside the range [-(2**53)+1, (2**53)-1]
• 205: Move CLI to its own package
• 240: ESM module export differs from main export
• 363: json5
• 357: VS Code extension
• 232: Very long string crash nodejs
• 350: Missing LICENSE file in the repo of ver 0.4.0
• 138: JSON5 TextMate bundle
• 122: Generate JSON5
• 346: CLI should process consecutive JSONs
• 345: Focus on ESNext
• 343: question: commented unreachable code
• 342: transitive dependency 'minimist' needs to be updated by rebuilding
• 339: Use .substring() instead of the deprecated .substr()
• 323: Provide exports config in packages.json
• 287: Module '"node_modules/json5/lib/index"' has no default export
• 185: Implement proposal-json-parse-with-source API
• 207: Add option to return objects as Maps to support ordered properties
• 91: Consider serializing RegExp objects to strings
• 150: Sync depedencies
• 234: Improvements in string parse
• 164: Possible performance improvements.
• 51: Portable test data set
• 85: The strings are not optimized on nodejs
• 239: Publishing Basic Performance Metrics Would be Helpful
• 119: Replace comments with spaces instead of stripping

The structured snapshot in .stackline/issue-triage.json also records recently closed reports. Issues for unrelated packages in shared monorepositories were qualified as outside this fork’s runtime scope. No maintainer was contacted.

Release changes

Unreleased [code, diff]

v2.2.3 [code, diff]

• Fix: json5@2.2.3 is now the 'latest' release according to npm instead of v1.0.2. (#299)

v2.2.2 [code, diff]

• Fix: Properties with the name __proto__ are added to objects and arrays. (#199) This also fixes a prototype pollution vulnerability reported by Jonathan Gregson! (#295).

v2.2.1 [code, diff]

• Fix: Removed dependence on minimist to patch CVE-2021-44906. (#266)

v2.2.0 [code, diff]

• New: Accurate and documented TypeScript declarations are now included. There is no need to install @types/json5. (#236, #244)

v2.1.3 [code, diff]

• Fix: An out of memory bug when parsing numbers has been fixed. (#228, #229)

v2.1.2 [code, diff]

• Fix: Bump minimist to v1.2.5. (#222)

v2.1.1 [code, diff]

• New: package.json and package.json5 include a module property so bundlers like webpack, rollup and parcel can take advantage of the ES Module build. (#208)
• Fix: stringify outputs \0 as \\x00 when followed by a digit. (#210)
• Fix: Spelling mistakes have been fixed. (#196)

v2.1.0 [code, diff]

• New: The index.mjs and index.min.mjs browser builds in the dist directory support ES6 modules. (#187)

v2.0.1 [code, diff]

• Fix: The browser builds in the dist directory support ES5. (#182)

v2.0.0 [code, diff]

• Major: JSON5 officially supports Node.js v6 and later. Support for Node.js v4 has been dropped. Since Node.js v6 supports ES5 features, the code has been rewritten in native ES5, and the dependence on Babel has been eliminated.

• New: Support for Unicode 10 has been added.

• New: The test framework has been migrated from Mocha to Tap.

• New: The browser build at dist/index.js is no longer minified by default. A minified version is available at dist/index.min.js. (#181)

• Fix: The warning has been made clearer when line and paragraph separators are used in strings.

• Fix: package.json5 has been restored, and it is automatically generated and committed when the version is bumped. A new build-package NPM script has been added to facilitate this.

v1.0.1 [code, diff]

This release includes a bug fix and minor change.

• Fix: parse throws on unclosed objects and arrays.

• New: package.json5 has been removed until an easier way to keep it in sync with package.json is found.

v1.0.0 [code, diff]

This release includes major internal changes and public API enhancements.

• Major: JSON5 officially supports Node.js v4 and later. Support for Node.js v0.10 and v0.12 have been dropped.

• New: Unicode property names and Unicode escapes in property names are supported. (#1)

• New: stringify outputs trailing commas in objects and arrays when a space option is provided. (#66)

• New: JSON5 allows line and paragraph separator characters (U+2028 and U+2029) in strings in order to be compatible with JSON. However, ES5 does not allow these characters in strings, so JSON5 gives a warning when they are parsed and escapes them when they are stringified. (#70)

• New: stringify accepts an options object as its second argument. The supported options are replacer, space, and a new quote option that specifies the quote character used in strings. (#71)

• New: The CLI supports STDIN and STDOUT and adds --out-file, --space, and --validate options. See json5 --help for more information. (#72, #84, and #108)

• New: In addition to the white space characters space \t, \v, \f, \n, \r, and \xA0, the additional white space characters \u2028, \u2029, and all other characters in the Space Separator Unicode category are allowed.

• New: In addition to the character escapes \', \", \\, \b, \f, \n, \r, and \t, the additional character escapes \v and \0, hexadecimal escapes like \x0F, and unnecessary escapes like \a are allowed in string values and string property names.

• New: stringify outputs strings with single quotes by default but intelligently uses double quotes if there are more single quotes than double quotes inside the string. (i.e. stringify('Stay here.') outputs 'Stay here.' while stringify('Let\'s go.') outputs "Let's go.")

• New: When a character is not allowed in a string, stringify outputs a character escape like \t when available, a hexadecimal escape like \x0F when the Unicode code point is less than 256, or a Unicode character escape like \u01FF, in that order.

• New: stringify checks for a toJSON5 method on objects and, if it exists, stringifies its return value instead of the object. toJSON5 overrides toJSON if they both exist.

• New: To require or import JSON5 files, use require('json5/lib/register') or import 'json5/lib/register'. Previous versions used json5/lib/require, which still exists for backward compatibility but is deprecated and will give a warning.

• New: To use JSON5 in browsers, use the file at dist/index.js or https://unpkg.com/json5@^1.0.0.

• Fix: stringify properly outputs Infinity and NaN. (#67)

• Fix: isWord no longer becomes a property of JSON5 after calling stringify. (#68 and #89)

• Fix: stringify no longer throws when an object does not have a prototype. (#154)

• Fix: stringify properly handles the key argument of toJSON(key) methods. toJSON5(key) follows this pattern.

• Fix: stringify accepts Number and String objects as its space argument.

• Fix: In addition to a function, stringify also accepts an array of keys to include in the output as its replacer argument. Numbers, Number objects, and String objects will be converted to a string if they are given as array values.

v0.5.1 [code, diff]

This release includes a minor fix for indentations when stringifying empty arrays.

• Fix: Indents no longer appear in empty arrays when stringified. (#134)

v0.5.0 [code, diff]

This release includes major internal changes and public API enhancements.

• Major: JSON5 officially supports Node.js v4 LTS and v5. Support for Node.js v0.6 and v0.8 have been dropped, while support for v0.10 and v0.12 remain.

• Fix: YUI Compressor no longer fails when compressing json5.js. (#97)

• New: parse and the CLI provide line and column numbers when displaying error messages. (#101; awesome work by @amb26.)

v0.4.0 [code, diff]

Note that v0.3.0 was tagged, but never published to npm, so this v0.4.0 changelog entry includes v0.3.0 features.

This is a massive release that adds stringify support, among other things.

• Major: JSON5.stringify() now exists! This method is analogous to the native JSON.stringify(); it just avoids quoting keys where possible. See the usage documentation for more. (#32; huge thanks and props @aeisenberg!)

• New: NaN and -NaN are now allowed number literals. (#30; thanks @rowanhill.)

• New: Duplicate object keys are now allowed; the last value is used. This is the same behavior as JSON. (#57; thanks @jordanbtucker.)

• Fix: Properly handle various whitespace and newline cases now. E.g. JSON5 now properly supports escaped CR and CRLF newlines in strings, and JSON5 now accepts the same whitespace as JSON (stricter than ES5). (#58, #60, and #63; thanks @jordanbtucker.)

• New: Negative hexadecimal numbers (e.g. -0xC8) are allowed again. (They were disallowed in v0.2.0; see below.) It turns out they are valid in ES5, so JSON5 supports them now too. (#36; thanks @jordanbtucker!)

v0.2.0 [code, diff]

This release fixes some bugs and adds some more utility features to help you express data more easily:

• Breaking: Negative hexadecimal numbers (e.g. -0xC8) are rejected now. While V8 (e.g. Chrome and Node) supported them, it turns out they're invalid in ES5. This has been fixed in V8 (and by extension, Chrome and Node), so JSON5 officially rejects them now, too. (#36)

• New: Trailing decimal points in decimal numbers are allowed again. (They were disallowed in v0.1.0; see below.) They're allowed by ES5, and differentiating between integers and floats may make sense on some platforms. (#16; thanks @Midar.)

• New: Infinity and -Infinity are now allowed number literals. (#30; thanks @pepkin88.)

• New: Plus signs (+) in front of numbers are now allowed, since it can be helpful in some contexts to explicitly mark numbers as positive. (E.g. when a property represents changes or deltas.)

• Fix: unescaped newlines in strings are rejected now. (#24; thanks @Midar.)

v0.1.0 [code, diff]

This release tightens JSON5 support and adds helpful utility features:

• New: Support hexadecimal numbers. (Thanks @MaxNanasy.)

• Fix: Reject octal numbers properly now. Previously, they were accepted but improperly parsed as base-10 numbers. (Thanks @MaxNanasy.)

• Breaking: Reject "noctal" numbers now (base-10 numbers that begin with a leading zero). These are disallowed by both JSON5 and JSON, as well as by ES5's strict mode. (Thanks @MaxNanasy.)

• New: Support leading decimal points in decimal numbers. (Thanks @MaxNanasy.)

• Breaking: Reject trailing decimal points in decimal numbers now. These are disallowed by both JSON5 and JSON. (Thanks @MaxNanasy.)

• Breaking: Reject omitted elements in arrays now. These are disallowed by both JSON5 and JSON.

• Fix: Throw proper SyntaxError instances on errors now.

• New: Add Node.js require() hook. Register via json5/lib/require.

• New: Add Node.js json5 executable to compile JSON5 files to JSON.

v0.0.1 [code, diff]

This was the first implementation of this JSON5 parser.

• Support unquoted object keys, including reserved words. Unicode characters and escape sequences sequences aren't yet supported.

• Support single-quoted strings.

• Support multi-line strings.

• Support trailing commas in arrays and objects.

• Support comments, both inline and block.

v0.0.0 [code]

Let's consider this to be Douglas Crockford's original json_parse.js — a parser for the regular JSON format.

Release files and references

• README.md
• UPSTREAM.md
• CHANGELOG.md
• LICENSE.md
• Package and publication metadata
• Full text documentation

Package bytes, npm provenance and the immutable GitHub release were verified for this version. Security checks describe the reviewed release; documented compatibility risks and upstream reports are not blanket claims of resolution.