# yargs-parser

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The mighty option parser used by [yargs](https://github.com/yargs/yargs).

visit the [yargs website](http://yargs.js.org/) for more examples, and thorough usage instructions.

<img width="250" src="https://raw.githubusercontent.com/yargs/yargs-parser/master/yargs-logo.png">

## Example

```sh
npm i yargs-parser --save
```

```js
const argv = require('yargs-parser')(process.argv.slice(2))
console.log(argv)
```

```sh
node example.js --foo=33 --bar hello
{ _: [], foo: 33, bar: 'hello' }
```

_or parse a string!_

```js
const argv = require('yargs-parser')('--foo=99 --bar=33')
console.log(argv)
```

```sh
{ _: [], foo: 99, bar: 33 }
```

Convert an array of mixed types before passing to `yargs-parser`:

```js
const parse = require('yargs-parser')
parse(['-f', 11, '--zoom', 55].join(' '))   // <-- array to string
parse(['-f', 11, '--zoom', 55].map(String)) // <-- array of strings
```

## Deno Example

As of `v19` `yargs-parser` supports [Deno](https://github.com/denoland/deno):

```typescript
import parser from "https://deno.land/x/yargs_parser/deno.ts";

const argv = parser('--foo=99 --bar=9987930', {
  string: ['bar']
})
console.log(argv)
```

## ESM Example

As of `v19` `yargs-parser` supports ESM (_both in Node.js and in the browser_):

**Node.js:**

```js
import parser from 'yargs-parser'

const argv = parser('--foo=99 --bar=9987930', {
  string: ['bar']
})
console.log(argv)
```

**Browsers:**

```html
<!doctype html>
<body>
  <script type="module">
    import parser from "https://unpkg.com/yargs-parser@19.0.0/browser.js";

    const argv = parser('--foo=99 --bar=9987930', {
      string: ['bar']
    })
    console.log(argv)
  </script>
</body>
```

## API

### parser(args, opts={})

Parses command line arguments returning a simple mapping of keys and values.

**expects:**

* `args`: a string or array of strings representing the options to parse.
* `opts`: provide a set of hints indicating how `args` should be parsed:
  * `opts.alias`: an object representing the set of aliases for a key: `{alias: {foo: ['f']}}`.
  * `opts.array`: indicate that keys should be parsed as an array: `{array: ['foo', 'bar']}`.<br>
    Indicate that keys should be parsed as an array and coerced to booleans / numbers:<br>
    `{array: [{ key: 'foo', boolean: true }, {key: 'bar', number: true}]}`.
  * `opts.boolean`: arguments should be parsed as booleans: `{boolean: ['x', 'y']}`.
  * `opts.coerce`: provide a custom synchronous function that returns a coerced value from the argument provided
    (or throws an error). For arrays the function is called only once for the entire array:<br>
    `{coerce: {foo: function (arg) {return modifiedArg}}}`.
  * `opts.config`: indicate a key that represents a path to a configuration file (this file will be loaded and parsed).
  * `opts.configObjects`: configuration objects to parse, their properties will be set as arguments:<br>
    `{configObjects: [{'x': 5, 'y': 33}, {'z': 44}]}`.
  * `opts.configuration`: provide configuration options to the yargs-parser (see: [configuration](#configuration)).
  * `opts.count`: indicate a key that should be used as a counter, e.g., `-vvv` = `{v: 3}`.
  * `opts.default`: provide default values for keys: `{default: {x: 33, y: 'hello world!'}}`.
  * `opts.envPrefix`: environment variables (`process.env`) with the prefix provided should be parsed.
  * `opts.narg`: specify that a key requires `n` arguments: `{narg: {x: 2}}`.
  * `opts.normalize`: `path.normalize()` will be applied to values set to this key.
  * `opts.number`: keys should be treated as numbers.
  * `opts.string`: keys should be treated as strings (even if they resemble a number `-x 33`).

**returns:**

* `obj`: an object representing the parsed value of `args`
  * `key/value`: key value pairs for each argument and their aliases.
  * `_`: an array representing the positional arguments.
  * [optional] `--`:  an array with arguments after the end-of-options flag `--`.

### require('yargs-parser').detailed(args, opts={})

Parses a command line string, returning detailed information required by the
yargs engine.

**expects:**

* `args`: a string or array of strings representing options to parse.
* `opts`: provide a set of hints indicating how `args`, inputs are identical to `require('yargs-parser')(args, opts={})`.

**returns:**

* `argv`: an object representing the parsed value of `args`
  * `key/value`: key value pairs for each argument and their aliases.
  * `_`: an array representing the positional arguments.
  * [optional] `--`:  an array with arguments after the end-of-options flag `--`.
* `error`: populated with an error object if an exception occurred during parsing.
* `aliases`: the inferred list of aliases built by combining lists in `opts.alias`.
* `newAliases`: any new aliases added via camel-case expansion:
  * `boolean`: `{ fooBar: true }`
* `defaulted`: any new argument created by `opts.default`, no aliases included.
  * `boolean`: `{ foo: true }`
* `configuration`: given by default settings and `opts.configuration`.

<a name="configuration"></a>

### Configuration

The yargs-parser applies several automated transformations on the keys provided
in `args`. These features can be turned on and off using the `configuration` field
of `opts`.

```js
var parsed = parser(['--no-dice'], {
  configuration: {
    'boolean-negation': false
  }
})
```

### short option groups

* default: `true`.
* key: `short-option-groups`.

Should a group of short-options be treated as boolean flags?

```sh
node example.js -abc
{ _: [], a: true, b: true, c: true }
```

_if disabled:_

```sh
node example.js -abc
{ _: [], abc: true }
```

### camel-case expansion

* default: `true`.
* key: `camel-case-expansion`.

Should hyphenated arguments be expanded into camel-case aliases?

```sh
node example.js --foo-bar
{ _: [], 'foo-bar': true, fooBar: true }
```

_if disabled:_

```sh
node example.js --foo-bar
{ _: [], 'foo-bar': true }
```

### dot-notation

* default: `true`
* key: `dot-notation`

Should keys that contain `.` be treated as objects?

```sh
node example.js --foo.bar
{ _: [], foo: { bar: true } }
```

_if disabled:_

```sh
node example.js --foo.bar
{ _: [], "foo.bar": true }
```

### parse numbers

* default: `true`
* key: `parse-numbers`

Should keys that look like numbers be treated as such?

```sh
node example.js --foo=99.3
{ _: [], foo: 99.3 }
```

_if disabled:_

```sh
node example.js --foo=99.3
{ _: [], foo: "99.3" }
```

### parse positional numbers

* default: `true`
* key: `parse-positional-numbers`

Should positional keys that look like numbers be treated as such.

```sh
node example.js 99.3
{ _: [99] }
```

_if disabled:_

```sh
node example.js 99.3
{ _: ['99.3'] }
```

### boolean negation

* default: `true`
* key: `boolean-negation`

Should variables prefixed with `--no` be treated as negations?

```sh
node example.js --no-foo
{ _: [], foo: false }
```

_if disabled:_

```sh
node example.js --no-foo
{ _: [], "no-foo": true }
```

### combine arrays

* default: `false`
* key: `combine-arrays`

Should arrays be combined when provided by both command line arguments and
a configuration file.

### duplicate arguments array

* default: `true`
* key: `duplicate-arguments-array`

Should arguments be coerced into an array when duplicated:

```sh
node example.js -x 1 -x 2
{ _: [], x: [1, 2] }
```

_if disabled:_

```sh
node example.js -x 1 -x 2
{ _: [], x: 2 }
```

### flatten duplicate arrays

* default: `true`
* key: `flatten-duplicate-arrays`

Should array arguments be coerced into a single array when duplicated:

```sh
node example.js -x 1 2 -x 3 4
{ _: [], x: [1, 2, 3, 4] }
```

_if disabled:_

```sh
node example.js -x 1 2 -x 3 4
{ _: [], x: [[1, 2], [3, 4]] }
```

### greedy arrays

* default: `true`
* key: `greedy-arrays`

Should arrays consume more than one positional argument following their flag.

```sh
node example --arr 1 2
{ _[], arr: [1, 2] }
```

_if disabled:_

```sh
node example --arr 1 2
{ _[2], arr: [1] }
```

**Note: in `v18.0.0` we are considering defaulting greedy arrays to `false`.**

### nargs eats options

* default: `false`
* key: `nargs-eats-options`

Should nargs consume dash options as well as positional arguments.

### negation prefix

* default: `no-`
* key: `negation-prefix`

The prefix to use for negated boolean variables.

```sh
node example.js --no-foo
{ _: [], foo: false }
```

_if set to `quux`:_

```sh
node example.js --quuxfoo
{ _: [], foo: false }
```

### populate --

* default: `false`.
* key: `populate--`

Should unparsed flags be stored in `--` or `_`.

_If disabled:_

```sh
node example.js a -b -- x y
{ _: [ 'a', 'x', 'y' ], b: true }
```

_If enabled:_

```sh
node example.js a -b -- x y
{ _: [ 'a' ], '--': [ 'x', 'y' ], b: true }
```

### set placeholder key

* default: `false`.
* key: `set-placeholder-key`.

Should a placeholder be added for keys not set via the corresponding CLI argument?

_If disabled:_

```sh
node example.js -a 1 -c 2
{ _: [], a: 1, c: 2 }
```

_If enabled:_

```sh
node example.js -a 1 -c 2
{ _: [], a: 1, b: undefined, c: 2 }
```

### halt at non-option

* default: `false`.
* key: `halt-at-non-option`.

Should parsing stop at the first positional argument? This is similar to how e.g. `ssh` parses its command line.

_If disabled:_

```sh
node example.js -a run b -x y
{ _: [ 'b' ], a: 'run', x: 'y' }
```

_If enabled:_

```sh
node example.js -a run b -x y
{ _: [ 'b', '-x', 'y' ], a: 'run' }
```

### strip aliased

* default: `false`
* key: `strip-aliased`

Should aliases be removed before returning results?

_If disabled:_

```sh
node example.js --test-field 1
{ _: [], 'test-field': 1, testField: 1, 'test-alias': 1, testAlias: 1 }
```

_If enabled:_

```sh
node example.js --test-field 1
{ _: [], 'test-field': 1, testField: 1 }
```

### strip dashed

* default: `false`
* key: `strip-dashed`

Should dashed keys be removed before returning results?  This option has no effect if
`camel-case-expansion` is disabled.

_If disabled:_

```sh
node example.js --test-field 1
{ _: [], 'test-field': 1, testField: 1 }
```

_If enabled:_

```sh
node example.js --test-field 1
{ _: [], testField: 1 }
```

### unknown options as args

* default: `false`
* key: `unknown-options-as-args`

Should unknown options be treated like regular arguments?  An unknown option is one that is not
configured in `opts`.

_If disabled_

```sh
node example.js --unknown-option --known-option 2 --string-option --unknown-option2
{ _: [], unknownOption: true, knownOption: 2, stringOption: '', unknownOption2: true }
```

_If enabled_

```sh
node example.js --unknown-option --known-option 2 --string-option --unknown-option2
{ _: ['--unknown-option'], knownOption: 2, stringOption: '--unknown-option2' }
```

## Supported Node.js Versions

Libraries in this ecosystem make a best effort to track
[Node.js' release schedule](https://nodejs.org/en/about/releases/). Here's [a
post on why we think this is important](https://medium.com/the-node-js-collection/maintainers-should-consider-following-node-js-release-schedule-ab08ed4de71a).

## Special Thanks

The yargs project evolves from optimist and minimist. It owes its
existence to a lot of James Halliday's hard work. Thanks [substack](https://github.com/substack) **beep** **boop** \o/

## License

ISC
