JSON5 – JSON for Humans (with support for undefined)

Fork Extention

This is a fork of the JSON5 project that adds support for parsing and serializing the JavaScript/ECMAScript value undefined. Changes and additions that are specific to this fork are marked with the phrase Fork extension.

The JSON5 Data Interchange Format (JSON5) is a superset of JSON that aims to alleviate some of the limitations of JSON by expanding its syntax to include some productions from ECMAScript 5.1.

This JavaScript library is the official reference implementation for JSON5 parsing and serialization libraries.

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.

Undefined values (Fork Extension)

• The value undefined is allowed (in addition to null from standard JSON).

Short 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",
  propertiesCanBe: undefined,   // Fork Extension
}

Specification

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

Installation

Node.js

npm install json5-with-undefined

const JSON5 = require('json5-with-undefined')

Browsers

<script src="https://unpkg.com/json5@^2.0.0/dist/index.min.js"></script>

This will create a global JSON5 variable.

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.

(Fork Extension) JSON5.parse accepts the keyword undefined, similarly to the keyword null and sets properties and other values in the resulting object accordingly. This behavior is not configurable.

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.
  • useUndefined: (Fork Extension) If useUndefined is unset or falsey, the generated JSON5 string will contain no uses of the undefined keyword and will be identical to using JSON5.stringify from the upstream project. If useUndefined is truthy, properties and other values that are undefined will be stringified as the keyword undefined in the resulting JSON5 string.

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-with-undefined/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-with-undefined

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/adaptable/json5-with-undefined
cd json5-with-undefined
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.

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

License

MIT. See LICENSE.md for details.

Credits

Assem Kishore founded this project.

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.