JSON11 – JSON for Humans

JSON11 is an extension to the popular JSON and JSON5 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. 🙂)

Formally, the JSON5 Data Interchange Format is a superset of JSON (so valid JSON files will always be valid JSON11 and JSON5 files) that expands its syntax to include some productions from ECMAScript 11 (ES11). It's also a subset of ES11, so valid JSON11 files will always be valid ES11.*

Summary of Features

The following ECMAScript 11 features, which are not supported in JSON, have been extended to JSON11.

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.
• Optionally, long numerals can be converted to BigInt.

BigInts

• Arbitrary precision integers are allowed.

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 JSON11 format, please read the official specification.

Installation and Usage

Node.js

npm install json5

CommonJS

const JSON11 = require('json5')

Modules

import JSON11 from 'json5'

Browsers

UMD

<!-- This will create a global `JSON11` variable. -->
<script src="https://unpkg.com/json5@2/dist/index.min.js"></script>

Modules

<script type="module">
  import JSON11 from 'https://unpkg.com/json5@2/dist/index.min.mjs'
</script>

API

The JSON11 API is compatible with the JSON API.

JSON11.parse()

Parses a JSON11 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

JSON11.parse(text[, reviver])

Parameters

• text: The string to parse as JSON11.
• 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 JSON11 text.

JSON11.stringify()

Converts a JavaScript value to a JSON11 string, optionally replacing values if a replacer function is specified, or optionally including only the specified properties if a replacer array is specified.

Syntax

JSON11.stringify(value[, replacer[, space]])
JSON11.stringify(value[, options])

Parameters

• value: The value to convert to a JSON11 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 JSON11 string. If this value is null or not provided, all properties of the object are included in the resulting JSON11 string.
• space: A String or Number object that's used to insert white space into the output JSON11 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 JSON11 string representing the value.

Node.js require() JSON11 files

When using Node.js, you can require() JSON11 files by adding the following statement.

require('json5/lib/register')

Then you can load a JSON11 file with a Node.js require() statement. For example:

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

CLI

Since JSON is more widely used than JSON11, this package includes a CLI for converting JSON11 to JSON and for validating the syntax of JSON11 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 JSON11 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 JSON11 data format, please submit an issue to the official specification repository.

Note that we will never add any features that make JSON11 incompatible with ES5; that compatibility is a fundamental premise of JSON11.*

To report bugs or request features regarding this JavaScript implementation of JSON11, 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 JSON11 aims to be fully compatible with ES5, there is one exception where both JSON and JSON11 are not. Both JSON and JSON11 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 JSON11 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 JSON11 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 JSON11 more closely with ES5, wrote the official JSON11 specification, completely rewrote the codebase from the ground up, and is actively maintaining this project.