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 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.

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.