JSON5 – Modern JSON

JSON isn't the friendliest to write and maintain by hand. Keys need to be quoted; objects and arrays can't have trailing commas; comments aren't supported — even though none of these is the case with regular JavaScript today.

Restricting JSON to such a strict subset of "JavaScript object notation" made sense for making it a great data-exchange format, but JSON's usage has expanded beyond machine-to-machine communication.

JSON5 is a proposed extension to JSON that brings ES5 enhancements to its syntax. It remains a strict subset of JavaScript, adds no new data types, and is a strict superset of existing JSON.

JSON5 is not an official successor to JSON, and existing JSON parsers may not understand these new features. It's thus recommended that files use a new extension like .json5 to be explicit. [TODO: New MIME type too?]

This module provides a JavaScript implementation that works on all modern JS engines (even IE6). Its parser is based directly off of Douglas Crockford's eval-free json_parse.js, making it both secure and robust. Give it a try!

Features

These are the new features of JSON5's syntax. All of these are optional, and all of these are part of ES5 JavaScript.

Object keys don't need to be quoted if they're valid identifiers. Yes, even reserved keywords are valid unquoted keys in ES5 [§11.1.5, §7.6]. [TODO: Unicode characters and escape sequences aren't yet supported in this implementation.]
Strings can be single-quoted.
Strings can be split across multiple lines; just prefix each newline with a backslash. [ES5 §7.8.4]
Objects and arrays can have trailing commas.
Both inline (single-line) and block (multi-line) comments are allowed.
Numbers can be hexadecimal (base 16), and they can also begin with a leading decimal (e.g. .5).

Example

{
    foo: 'bar',
    while: true,
    
    this: 'is a\
 multi-line string',
 
    // this is an inline comment
    here: 'is another', // inline comment
    
    /* this is a block comment
       that continues on another line */

    hex: 0xDEADbeef,
    half: .5,
       
    finally: 'a trailing comma',
    oh: [
        "we shouldn't forget",
        'arrays can have',
        'trailing commas too',
    ],
}

Installation

Via npm on Node:

npm install json5

var JSON5 = require('json5');

Or in the browser (adds the JSON5 object to the global namespace):

<script src="json5.js"></script>

Usage

var obj = JSON5.parse('{unquoted:"key",trailing:"comma",}');
var str = JSON5.stringify(obj);
console.log(obj);
console.log(str);

JSON5.stringify() is currently aliased to the native JSON.stringify() in order for the output to be fully compatible with all JSON parsers today.

If you're running Node, you can also register a JSON5 require() hook to let you require() .json5 files just like you can .json files:

require('json5/lib/require');
require('./path/to/foo');   // tries foo.json5 after foo.js, foo.json, etc.
require('./path/to/bar.json5');

This module also provides a json5 executable (requires Node) for converting JSON5 files to sibling JSON files:

$ json5 -c path/to/foo.json5    # generates path/to/foo.json

Development

git clone git://github.com/aseemk/json5.git
cd json5
make
make test

If your system doesn't have Make, this should work in place of make [test]:

./lib/cli.js -c package.json5
npm install
npm test

Make is used to auto-generate the package.json file that npm requires from our package.json5 file. Just re-run make (or ./lib/cli.js -c package.json5) on changes to package.json5.

Feel free to file issues and submit pull requests — contributions are welcome.

If you submit a pull request, please be sure to add or update corresponding test cases, and ensure that make test (or npm test) continues to pass.

License

Credits

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 me motivation and confidence that building a new parser to implement these ideas this was within my reach! This code is also modeled directly off of Doug's open-source json_parse.js parser. I'm super grateful for that clean and well-documented code.

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

MaxNanasy/json5