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# JSON5 Modern JSON
JSON is an excellent data format, but we think it can be better.
**JSON5 is a proposed extension to JSON** that aims to make it easier for
*humans to write and maintain* by hand. It does this by adding some minimal
syntax features directly from ECMAScript 5.
JSON5 remains a **strict subset of JavaScript**, adds **no new data types**,
and **works with all existing JSON content**.
JSON5 is *not* an official successor to JSON, and JSON5 content may *not*
work with existing JSON parsers. For this reason, JSON5 files use a new .json5
extension. *(TODO: new MIME type needed too.)*
The code here is a **reference JavaScript implementation** for both Node.js
and all browsers. It's based directly off of Douglas Crockford's own [JSON
implementation][json_parse.js], and it's both robust and secure.
## Why
JSON isn't the friendliest to *write*. Keys need to be quoted, objects and
arrays can't have trailing commas, and comments aren't allowed — even though
none of these are the case with regular JavaScript today.
That was fine when JSON's goal was to be a great data format, but JSON's usage
has expanded beyond *machines*. JSON is now used for writing [configs][ex1],
[manifests][ex2], even [tests][ex3] — all by *humans*.
[ex1]: http://plovr.com/docs.html
[ex2]: http://npmjs.org/doc/json.html
[ex3]: http://code.google.com/p/fuzztester/wiki/JSONFileFormat
There are other formats that are human-friendlier, like YAML, but changing
from JSON to a completely different format is undesirable in many cases.
JSON5s aim is to remain close to JSON and JavaScript.
## Features
The following is the exact list of additions to JSON's syntax introduced by
JSON5. **All of these are optional**, and **all of these come from ES5**.
### Objects
- Object keys can be unquoted if they're valid [identifiers][mdn_variables].
Yes, even reserved keywords (like `default`) are valid unquoted keys in ES5
[[§11.1.5](http://es5.github.com/#x11.1.5), [§7.6](http://es5.github.com/#x7.6)].
*(TODO: Unicode characters and escape sequences arent yet supported in this
implementation.)*
- Objects can have trailing commas.
[mdn_variables]: https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Core_Language_Features#Variables
### Arrays
- Arrays can have trailing commas.
### Strings
- Strings can be single-quoted.
- Strings can be split across multiple lines; just prefix each newline with a
backslash. [ES5 [§7.8.4](http://es5.github.com/#x7.8.4)]
### Numbers
- Numbers can be hexadecimal (base 16). (But note that neither signed
hexadecimals nor hexadecimal floats are allowed by ES5.)
- Numbers can begin or end with a (leading or trailing) decimal point.
- Numbers can include `Infinity` and `-Infinity`.
- Numbers can begin with an explicit plus sign.
### Comments
- Both inline (single-line) and block (multi-line) comments are allowed.
## Example
The following is a contrived example, but it illustrates most of the features:
```js
{
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,
delta: +10,
to: Infinity, // and beyond!
finally: 'a trailing comma',
oh: [
"we shouldn't forget",
'arrays can have',
'trailing commas too',
],
}
```
This implementation's own [package.json5](package.json5) is more realistic:
```js
// This file is written in JSON5 syntax, naturally, but npm needs a regular
// JSON file, so compile via `npm run build`. Be sure to keep both in sync!
{
name: 'json5',
version: '0.2.0',
description: 'JSON for the ES5 era.',
keywords: ['json', 'es5'],
author: 'Aseem Kishore <aseem.kishore@gmail.com>',
contributors: [
'Max Nanasy <max.nanasy@gmail.com>',
],
main: 'lib/json5.js',
bin: 'lib/cli.js',
dependencies: {},
devDependencies: {
mocha: '~1.0.3',
},
scripts: {
build: './lib/cli.js -c package.json5',
test: 'mocha --ui exports --reporter spec',
},
homepage: 'http://json5.org/',
repository: {
type: 'git',
url: 'https://github.com/aseemk/json5.git',
},
}
```
## Community
Join the [Google Group](http://groups.google.com/group/json5) if you're
interested in JSON5 news, updates, and general discussion.
Don't worry, it's very low-traffic.
The [GitHub wiki](https://github.com/aseemk/json5/wiki) is a good place to track
JSON5 support and usage. Contribute freely there!
[GitHub Issues](https://github.com/aseemk/json5/issues) is the place to
formally propose feature requests and report bugs. Questions and general
feedback are better directed at the Google Group.
## Usage
This JavaScript implementation of JSON5 simply provides a `JSON5` object just
like the native ES5 `JSON` object.
To use from Node:
```
npm install json5
```
```js
var JSON5 = require('json5');
```
To use in the browser (adds the `JSON5` object to the global namespace):
```
<script src="json5.js"></script>
```
Then in both cases, you can simply replace native `JSON` calls with `JSON5`:
```js
var obj = JSON5.parse('{unquoted:"key",trailing:"comma",}');
var str = JSON5.stringify(obj);
```
`JSON5.parse` supports all of the JSON5 features listed above (*TODO: except
Unicode*), as well as the native [`reviver` argument][json-parse].
[json-parse]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse
`JSON5.stringify` mainly avoids quoting keys where possible, but we hope to
keep expanding it in the future (e.g. to also output trailing commas).
It supports the native [`replacer` and `space` arguments][json-stringify],
as well. *(TODO: Any implemented `toJSON` methods aren't used today.)*
[json-stringify]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
### Extras
If you're running this on Node, you can also register a JSON5 `require()` hook
to let you `require()` `.json5` files just like you can `.json` files:
```js
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 JSON:
```
$ json5 -c path/to/foo.json5 # generates path/to/foo.json
```
## Development
```
git clone git://github.com/aseemk/json5.git
cd json5
npm install
npm test
```
As the `package.json5` file states, be sure to run `npm run build` on changes
to `package.json5`, since npm requires `package.json`.
Feel free to [file issues](https://github.com/aseemk/json5/issues) and submit
[pull requests](https://github.com/aseemk/json5/pulls) — contributions are
welcome. If you do submit a pull request, please be sure to add or update the
tests, and ensure that `npm test` continues to pass.
## License
MIT License. © 2012 Aseem Kishore, and [others](
https://github.com/aseemk/json5/contributors).
## Credits
[Michael Bolin](http://bolinfest.com/) independently arrived at and published
some of these same ideas with awesome explanations and detail.
Recommended reading:
[Suggested Improvements to JSON](http://bolinfest.com/essays/json.html)
[Douglas Crockford](http://www.crockford.com/) of course designed and built
JSON, but his state machine diagrams on the [JSON website](http://json.org/),
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.
[json_parse.js]: https://github.com/douglascrockford/JSON-js/blob/master/json_parse.js
[Max Nanasy](https://github.com/MaxNanasy) has been an early and prolific
supporter, contributing multiple patches and ideas. Thanks Max!
[Andrew Eisenberg](https://github.com/aeisenberg) has contributed the `stringify` method.