287 lines
8.7 KiB
Markdown
287 lines
8.7 KiB
Markdown
# JSON5 – Modern JSON
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[](https://travis-ci.org/json5/json5)
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JSON is an excellent data format, but we think it can be better.
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**JSON5 is a proposed extension to JSON** that aims to make it easier for
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*humans to write and maintain* by hand. It does this by adding some minimal
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syntax features directly from ECMAScript 5.
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JSON5 remains a **strict subset of JavaScript**, adds **no new data types**,
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and **works with all existing JSON content**.
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JSON5 is *not* an official successor to JSON, and JSON5 content may *not*
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work with existing JSON parsers. For this reason, JSON5 files use a new .json5
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extension. *(TODO: new MIME type needed too.)*
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The code here is a **reference JavaScript implementation** for both Node.js
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and all browsers. It’s based directly off of Douglas Crockford’s own [JSON
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implementation][json_parse.js], and it’s both robust and secure.
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## Why
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JSON isn’t the friendliest to *write*. Keys need to be quoted, objects and
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arrays can’t have trailing commas, and comments aren’t allowed — even though
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none of these are the case with regular JavaScript today.
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That was fine when JSON’s goal was to be a great data format, but JSON’s usage
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has expanded beyond *machines*. JSON is now used for writing [configs][ex1],
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[manifests][ex2], even [tests][ex3] — all by *humans*.
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[ex1]: http://plovr.com/docs.html
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[ex2]: https://www.npmjs.org/doc/files/package.json.html
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[ex3]: http://code.google.com/p/fuzztester/wiki/JSONFileFormat
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There are other formats that are human-friendlier, like YAML, but changing
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from JSON to a completely different format is undesirable in many cases.
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JSON5’s aim is to remain close to JSON and JavaScript.
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## Features
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The following is the exact list of additions to JSON’s syntax introduced by
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JSON5. **All of these are optional**, and **all of these come from ES5**.
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### Objects
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- Object keys can be unquoted if they’re valid [identifiers][mdn_variables].
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Yes, even reserved keywords (like `default`) are valid unquoted keys in ES5
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[[§11.1.5](http://es5.github.com/#x11.1.5), [§7.6](http://es5.github.com/#x7.6)].
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([More info](https://mathiasbynens.be/notes/javascript-identifiers))
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*(TODO: Unicode characters and escape sequences aren’t yet supported in this
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implementation.)*
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- Object keys can also be single-quoted.
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- Objects can have trailing commas.
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[mdn_variables]: https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Core_Language_Features#Variables
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### Arrays
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- Arrays can have trailing commas.
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### Strings
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- Strings can be single-quoted.
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- Strings can be split across multiple lines; just prefix each newline with a
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backslash. [ES5 [§7.8.4](http://es5.github.com/#x7.8.4)]
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### Numbers
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- Numbers can be hexadecimal (base 16).
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- Numbers can begin or end with a (leading or trailing) decimal point.
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- Numbers can include `Infinity`, `-Infinity`, `NaN`, and `-NaN`.
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- Numbers can begin with an explicit plus sign.
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### Comments
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- Both inline (single-line) and block (multi-line) comments are allowed.
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## Example
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The following is a contrived example, but it illustrates most of the features:
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```js
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{
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foo: 'bar',
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while: true,
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this: 'is a \
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multi-line string',
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// this is an inline comment
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here: 'is another', // inline comment
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/* this is a block comment
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that continues on another line */
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hex: 0xDEADbeef,
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half: .5,
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delta: +10,
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to: Infinity, // and beyond!
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finally: 'a trailing comma',
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oh: [
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"we shouldn't forget",
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'arrays can have',
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'trailing commas too',
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],
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}
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```
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This implementation’s own [package.json5](package.json5) is more realistic:
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```js
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// This file is written in JSON5 syntax, naturally, but npm needs a regular
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// JSON file, so compile via `npm run build`. Be sure to keep both in sync!
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{
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name: 'json5',
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version: '0.5.0',
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description: 'JSON for the ES5 era.',
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keywords: ['json', 'es5'],
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author: 'Aseem Kishore <aseem.kishore@gmail.com>',
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contributors: [
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// TODO: Should we remove this section in favor of GitHub's list?
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// https://github.com/aseemk/json5/contributors
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'Max Nanasy <max.nanasy@gmail.com>',
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'Andrew Eisenberg <andrew@eisenberg.as>',
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'Jordan Tucker <jordanbtucker@gmail.com>',
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],
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main: 'lib/json5.js',
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bin: 'lib/cli.js',
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files: ["lib/"],
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dependencies: {},
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devDependencies: {
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gulp: "^3.9.1",
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'gulp-jshint': "^2.0.0",
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jshint: "^2.9.1",
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'jshint-stylish': "^2.1.0",
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mocha: "^2.4.5"
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},
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scripts: {
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build: 'node ./lib/cli.js -c package.json5',
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test: 'mocha --ui exports --reporter spec',
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// TODO: Would it be better to define these in a mocha.opts file?
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},
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homepage: 'http://json5.org/',
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license: 'MIT',
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repository: {
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type: 'git',
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url: 'https://github.com/aseemk/json5.git',
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},
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}
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```
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## Community
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Join the [Google Group](http://groups.google.com/group/json5) if you’re
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interested in JSON5 news, updates, and general discussion.
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Don’t worry, it’s very low-traffic.
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The [GitHub wiki](https://github.com/aseemk/json5/wiki) is a good place to track
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JSON5 support and usage. Contribute freely there!
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[GitHub Issues](https://github.com/aseemk/json5/issues) is the place to
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formally propose feature requests and report bugs. Questions and general
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feedback are better directed at the Google Group.
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## Usage
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This JavaScript implementation of JSON5 simply provides a `JSON5` object just
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like the native ES5 `JSON` object.
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To use from Node:
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```sh
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npm install json5
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```
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```js
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var JSON5 = require('json5');
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```
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To use in the browser (adds the `JSON5` object to the global namespace):
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```html
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<script src="json5.js"></script>
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```
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Then in both cases, you can simply replace native `JSON` calls with `JSON5`:
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```js
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var obj = JSON5.parse('{unquoted:"key",trailing:"comma",}');
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var str = JSON5.stringify(obj);
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```
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`JSON5.parse` supports all of the JSON5 features listed above (*TODO: except
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Unicode*), as well as the native [`reviver` argument][json-parse].
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[json-parse]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse
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`JSON5.stringify` mainly avoids quoting keys where possible, but we hope to
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keep expanding it in the future (e.g. to also output trailing commas).
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It supports the native [`replacer` and `space` arguments][json-stringify],
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as well. *(TODO: Any implemented `toJSON` methods aren’t used today.)*
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[json-stringify]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
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### Extras
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If you’re running this on Node, you can also register a JSON5 `require()` hook
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to let you `require()` `.json5` files just like you can `.json` files:
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```js
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require('json5/lib/require');
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require('./path/to/foo'); // tries foo.json5 after foo.js, foo.json, etc.
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require('./path/to/bar.json5');
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```
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This module also provides a `json5` executable (requires Node) for converting
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JSON5 files to JSON:
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```sh
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json5 -c path/to/foo.json5 # generates path/to/foo.json
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```
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## Development
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```sh
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git clone git://github.com/aseemk/json5.git
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cd json5
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npm install
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npm test
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```
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As the `package.json5` file states, be sure to run `npm run build` on changes
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to `package.json5`, since npm requires `package.json`.
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Feel free to [file issues](https://github.com/aseemk/json5/issues) and submit
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[pull requests](https://github.com/aseemk/json5/pulls) — contributions are
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welcome. If you do submit a pull request, please be sure to add or update the
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tests, and ensure that `npm test` continues to pass.
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## License
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MIT. See [LICENSE.md](./LICENSE.md) for details.
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## Credits
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[Michael Bolin](http://bolinfest.com/) independently arrived at and published
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some of these same ideas with awesome explanations and detail.
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Recommended reading:
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[Suggested Improvements to JSON](http://bolinfest.com/essays/json.html)
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[Douglas Crockford](http://www.crockford.com/) of course designed and built
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JSON, but his state machine diagrams on the [JSON website](http://json.org/),
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as cheesy as it may sound, gave me motivation and confidence that building a
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new parser to implement these ideas this was within my reach!
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This code is also modeled directly off of Doug’s open-source [json_parse.js][]
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parser. I’m super grateful for that clean and well-documented code.
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[json_parse.js]: https://github.com/douglascrockford/JSON-js/blob/master/json_parse.js
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[Max Nanasy](https://github.com/MaxNanasy) has been an early and prolific
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supporter, contributing multiple patches and ideas. Thanks Max!
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[Andrew Eisenberg](https://github.com/aeisenberg) has contributed the
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`stringify` method.
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[Jordan Tucker](https://github.com/jordanbtucker) has aligned JSON5 more closely
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with ES5 and is actively maintaining this project.
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