283 lines
10 KiB
Markdown
283 lines
10 KiB
Markdown
# JSON5 – JSON for Humans
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[][Build
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Status] [][Coverage
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Status]
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JSON5 is an extension to the popular [JSON] file format that aims to be
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easier to **write and maintain _by hand_ (e.g. for config files)**.
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It is _not intended_ to be used for machine-to-machine communication.
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(Keep using JSON or other file formats for that. 🙂)
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JSON5 was started in 2012, and as of 2022, now gets **[>65M downloads/week](https://www.npmjs.com/package/json5)**,
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ranks in the **[top 0.1%](https://gist.github.com/anvaka/8e8fa57c7ee1350e3491)** of the most depended-upon packages on npm,
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and has been adopted by major projects like
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**[Chromium](https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/platform/runtime_enabled_features.json5;drc=5de823b36e68fd99009a29281b17bc3a1d6b329c),
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[Next.js](https://github.com/vercel/next.js/blob/b88f20c90bf4659b8ad5cb2a27956005eac2c7e8/packages/next/lib/find-config.ts#L43-L46),
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[Babel](https://babeljs.io/docs/en/config-files#supported-file-extensions),
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[Retool](https://community.retool.com/t/i-am-attempting-to-append-several-text-fields-to-a-google-sheet-but-receiving-a-json5-invalid-character-error/7626),
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[WebStorm](https://www.jetbrains.com/help/webstorm/json.html),
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and [more](https://github.com/json5/json5/wiki/In-the-Wild)**.
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It's also natively supported on **[Apple platforms](https://developer.apple.com/documentation/foundation/jsondecoder/3766916-allowsjson5)**
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like **MacOS** and **iOS**.
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Formally, the **[JSON5 Data Interchange Format](https://spec.json5.org/)** is a superset of JSON
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(so valid JSON files will always be valid JSON5 files)
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that expands its syntax to include some productions from [ECMAScript 5.1] (ES5).
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It's also a strict _subset_ of ES5, so valid JSON5 files will always be valid ES5.
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This JavaScript library is a reference implementation for JSON5 parsing and serialization,
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and is directly used in many of the popular projects mentioned above
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(where e.g. extreme performance isn't necessary),
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but others have created [many other libraries](https://github.com/json5/json5/wiki/In-the-Wild)
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across many other platforms.
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[Build Status]: https://app.travis-ci.com/json5/json5
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[Coverage Status]: https://coveralls.io/github/json5/json5
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[JSON]: https://tools.ietf.org/html/rfc7159
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[ECMAScript 5.1]: https://www.ecma-international.org/ecma-262/5.1/
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## Summary of Features
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The following ECMAScript 5.1 features, which are not supported in JSON, have
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been extended to JSON5.
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### Objects
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- Object keys may be an ECMAScript 5.1 _[IdentifierName]_.
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- Objects may have a single trailing comma.
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### Arrays
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- Arrays may have a single trailing comma.
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### Strings
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- Strings may be single quoted.
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- Strings may span multiple lines by escaping new line characters.
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- Strings may include character escapes.
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### Numbers
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- Numbers may be hexadecimal.
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- Numbers may have a leading or trailing decimal point.
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- Numbers may be [IEEE 754] positive infinity, negative infinity, and NaN.
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- Numbers may begin with an explicit plus sign.
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### Comments
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- Single and multi-line comments are allowed.
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### White Space
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- Additional white space characters are allowed.
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[IdentifierName]: https://www.ecma-international.org/ecma-262/5.1/#sec-7.6
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[IEEE 754]: http://ieeexplore.ieee.org/servlet/opac?punumber=4610933
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## Example
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Kitchen-sink example:
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```js
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{
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// comments
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unquoted: 'and you can quote me on that',
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singleQuotes: 'I can use "double quotes" here',
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lineBreaks: "Look, Mom! \
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No \\n's!",
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hexadecimal: 0xdecaf,
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leadingDecimalPoint: .8675309, andTrailing: 8675309.,
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positiveSign: +1,
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trailingComma: 'in objects', andIn: ['arrays',],
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"backwardsCompatible": "with JSON",
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}
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```
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A more real-world example is [this config file](https://github.com/chromium/chromium/blob/feb3c9f670515edf9a88f185301cbd7794ee3e52/third_party/blink/renderer/platform/runtime_enabled_features.json5)
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from the Chromium/Blink project.
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## Specification
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For a detailed explanation of the JSON5 format, please read the [official
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specification](https://json5.github.io/json5-spec/).
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## Installation and Usage
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### Node.js
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```sh
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npm install json5
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```
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#### CommonJS
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```js
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const JSON5 = require('json5')
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```
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#### Modules
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```js
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import JSON5 from 'json5'
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```
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### Browsers
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#### UMD
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```html
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<!-- This will create a global `JSON5` variable. -->
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<script src="https://unpkg.com/json5@2/dist/index.min.js"></script>
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```
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#### Modules
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```html
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<script type="module">
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import JSON5 from 'https://unpkg.com/json5@2/dist/index.min.mjs'
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</script>
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```
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## API
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The JSON5 API is compatible with the [JSON API].
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[JSON API]:
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON
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### JSON5.parse()
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Parses a JSON5 string, constructing the JavaScript value or object described by
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the string. An optional reviver function can be provided to perform a
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transformation on the resulting object before it is returned.
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#### Syntax
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JSON5.parse(text[, reviver])
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#### Parameters
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- `text`: The string to parse as JSON5.
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- `reviver`: If a function, this prescribes how the value originally produced by
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parsing is transformed, before being returned.
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#### Return value
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The object corresponding to the given JSON5 text.
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### JSON5.stringify()
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Converts a JavaScript value to a JSON5 string, optionally replacing values if a
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replacer function is specified, or optionally including only the specified
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properties if a replacer array is specified.
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#### Syntax
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JSON5.stringify(value[, replacer[, space]])
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JSON5.stringify(value[, options])
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#### Parameters
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- `value`: The value to convert to a JSON5 string.
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- `replacer`: A function that alters the behavior of the stringification
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process, or an array of String and Number objects that serve as a whitelist
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for selecting/filtering the properties of the value object to be included in
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the JSON5 string. If this value is null or not provided, all properties of the
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object are included in the resulting JSON5 string.
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- `space`: A String or Number object that's used to insert white space into the
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output JSON5 string for readability purposes. If this is a Number, it
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indicates the number of space characters to use as white space; this number is
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capped at 10 (if it is greater, the value is just 10). Values less than 1
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indicate that no space should be used. If this is a String, the string (or the
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first 10 characters of the string, if it's longer than that) is used as white
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space. If this parameter is not provided (or is null), no white space is used.
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If white space is used, trailing commas will be used in objects and arrays.
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- `options`: An object with the following properties:
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- `replacer`: Same as the `replacer` parameter.
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- `space`: Same as the `space` parameter.
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- `quote`: A String representing the quote character to use when serializing
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strings.
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#### Return value
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A JSON5 string representing the value.
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### Node.js `require()` JSON5 files
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When using Node.js, you can `require()` JSON5 files by adding the following
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statement.
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```js
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require('json5/lib/register')
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```
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Then you can load a JSON5 file with a Node.js `require()` statement. For
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example:
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```js
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const config = require('./config.json5')
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```
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## CLI
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Since JSON is more widely used than JSON5, this package includes a CLI for
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converting JSON5 to JSON and for validating the syntax of JSON5 documents.
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### Installation
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```sh
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npm install --global json5
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```
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### Usage
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```sh
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json5 [options] <file>
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```
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If `<file>` is not provided, then STDIN is used.
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#### Options:
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- `-s`, `--space`: The number of spaces to indent or `t` for tabs
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- `-o`, `--out-file [file]`: Output to the specified file, otherwise STDOUT
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- `-v`, `--validate`: Validate JSON5 but do not output JSON
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- `-V`, `--version`: Output the version number
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- `-h`, `--help`: Output usage information
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## Contributing
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### Development
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```sh
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git clone https://github.com/json5/json5
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cd json5
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npm install
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```
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When contributing code, please write relevant tests and run `npm test` and `npm
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run lint` before submitting pull requests. Please use an editor that supports
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[EditorConfig](http://editorconfig.org/).
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### Issues
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To report bugs or request features regarding the JSON5 **data format**,
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please submit an issue to the official
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**[_specification_ repository](https://github.com/json5/json5-spec)**.
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Note that we will never add any features that make JSON5 incompatible with ES5;
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that compatibility is a fundamental premise of JSON5.
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To report bugs or request features regarding this **JavaScript implementation**
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of JSON5, please submit an issue to **_this_ repository**.
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### Security Vulnerabilities and Disclosures
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To report a security vulnerability, please follow the follow the guidelines
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described in our [security policy](./SECURITY.md).
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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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[Aseem Kishore](https://github.com/aseemk) founded this project.
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He wrote a [blog post](https://aseemk.substack.com/p/ignore-the-f-ing-haters-json5)
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about the journey and lessons learned 10 years in.
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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. Recommended
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reading: [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/), as
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cheesy as it may sound, gave us motivation and confidence that building a new
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parser to implement these ideas was within reach! The original
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implementation of JSON5 was also modeled directly off of Doug’s open-source
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[json_parse.js] parser. We’re grateful for that clean and well-documented
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code.
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[json_parse.js]:
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https://github.com/douglascrockford/JSON-js/blob/03157639c7a7cddd2e9f032537f346f1a87c0f6d/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.
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[Andrew Eisenberg](https://github.com/aeisenberg) contributed the original
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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, wrote the official JSON5 specification, completely rewrote the
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codebase from the ground up, and is actively maintaining this project.
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