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JSON5 – JSON for Humans

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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 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

Arrays

Strings

Numbers

Comments

White Space

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

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

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:

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.

ECMAScript Compatibility

While JSON5 aims to be fully compatible with ES5, there is one exception where both JSON and JSON5 are not. Both JSON and JSON5 allow unescaped line and paragraph separator characters (U+2028 and U+2029) in strings, however ES5 does not. A proposal to allow these characters in strings was adopted into ES2019, making JSON and JSON5 fully compatible with ES2019.

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.