<!-- omit in toc -->
# parseArgs

[![Coverage][coverage-image]][coverage-url]

Polyfill of `util.parseArgs()`

## `util.parseArgs([config])`

<!-- YAML
added: v18.3.0
changes:
  - version: REPLACEME
    pr-url: https://github.com/nodejs/node/pull/43459
    description: add support for returning detailed parse information
                 using `tokens` in input `config` and returned properties.
-->

> Stability: 1 - Experimental

* `config` {Object} Used to provide arguments for parsing and to configure
  the parser. `config` supports the following properties:
  * `args` {string\[]} array of argument strings. **Default:** `process.argv`
    with `execPath` and `filename` removed.
  * `options` {Object} Used to describe arguments known to the parser.
    Keys of `options` are the long names of options and values are an
    {Object} accepting the following properties:
    * `type` {string} Type of argument, which must be either `boolean` or `string`.
    * `multiple` {boolean} Whether this option can be provided multiple
      times. If `true`, all values will be collected in an array. If
      `false`, values for the option are last-wins. **Default:** `false`.
    * `short` {string} A single character alias for the option.
    * `default` {string | boolean | string\[] | boolean\[]} The default option
      value when it is not set by args. It must be of the same type as the
      the `type` property. When `multiple` is `true`, it must be an array.
  * `strict` {boolean} Should an error be thrown when unknown arguments
    are encountered, or when arguments are passed that do not match the
    `type` configured in `options`.
    **Default:** `true`.
  * `allowPositionals` {boolean} Whether this command accepts positional
    arguments.
    **Default:** `false` if `strict` is `true`, otherwise `true`.
  * `tokens` {boolean} Return the parsed tokens. This is useful for extending
    the built-in behavior, from adding additional checks through to reprocessing
    the tokens in different ways.
    **Default:** `false`.

* Returns: {Object} The parsed command line arguments:
  * `values` {Object} A mapping of parsed option names with their {string}
    or {boolean} values.
  * `positionals` {string\[]} Positional arguments.
  * `tokens` {Object\[] | undefined} See [parseArgs tokens](#parseargs-tokens)
    section. Only returned if `config` includes `tokens: true`.

Provides a higher level API for command-line argument parsing than interacting
with `process.argv` directly. Takes a specification for the expected arguments
and returns a structured object with the parsed options and positionals.

```mjs
import { parseArgs } from 'node:util';
const args = ['-f', '--bar', 'b'];
const options = {
  foo: {
    type: 'boolean',
    short: 'f'
  },
  bar: {
    type: 'string'
  }
};
const {
  values,
  positionals
} = parseArgs({ args, options });
console.log(values, positionals);
// Prints: [Object: null prototype] { foo: true, bar: 'b' } []
```

```cjs
const { parseArgs } = require('node:util');
const args = ['-f', '--bar', 'b'];
const options = {
  foo: {
    type: 'boolean',
    short: 'f'
  },
  bar: {
    type: 'string'
  }
};
const {
  values,
  positionals
} = parseArgs({ args, options });
console.log(values, positionals);
// Prints: [Object: null prototype] { foo: true, bar: 'b' } []
```

`util.parseArgs` is experimental and behavior may change. Join the
conversation in [pkgjs/parseargs][] to contribute to the design.

### `parseArgs` `tokens`

Detailed parse information is available for adding custom behaviours by
specifying `tokens: true` in the configuration.
The returned tokens have properties describing:

* all tokens
  * `kind` {string} One of 'option', 'positional', or 'option-terminator'.
  * `index` {number} Index of element in `args` containing token. So the
    source argument for a token is `args[token.index]`.
* option tokens
  * `name` {string} Long name of option.
  * `rawName` {string} How option used in args, like `-f` of `--foo`.
  * `value` {string | undefined} Option value specified in args.
    Undefined for boolean options.
  * `inlineValue` {boolean | undefined} Whether option value specified inline,
    like `--foo=bar`.
* positional tokens
  * `value` {string} The value of the positional argument in args (i.e. `args[index]`).
* option-terminator token

The returned tokens are in the order encountered in the input args. Options
that appear more than once in args produce a token for each use. Short option
groups like `-xy` expand to a token for each option. So `-xxx` produces
three tokens.

For example to use the returned tokens to add support for a negated option
like `--no-color`, the tokens can be reprocessed to change the value stored
for the negated option.

```mjs
import { parseArgs } from 'node:util';

const options = {
  'color': { type: 'boolean' },
  'no-color': { type: 'boolean' },
  'logfile': { type: 'string' },
  'no-logfile': { type: 'boolean' },
};
const { values, tokens } = parseArgs({ options, tokens: true });

// Reprocess the option tokens and overwrite the returned values.
tokens
  .filter((token) => token.kind === 'option')
  .forEach((token) => {
    if (token.name.startsWith('no-')) {
      // Store foo:false for --no-foo
      const positiveName = token.name.slice(3);
      values[positiveName] = false;
      delete values[token.name];
    } else {
      // Resave value so last one wins if both --foo and --no-foo.
      values[token.name] = token.value ?? true;
    }
  });

const color = values.color;
const logfile = values.logfile ?? 'default.log';

console.log({ logfile, color });
```

```cjs
const { parseArgs } = require('node:util');

const options = {
  'color': { type: 'boolean' },
  'no-color': { type: 'boolean' },
  'logfile': { type: 'string' },
  'no-logfile': { type: 'boolean' },
};
const { values, tokens } = parseArgs({ options, tokens: true });

// Reprocess the option tokens and overwrite the returned values.
tokens
  .filter((token) => token.kind === 'option')
  .forEach((token) => {
    if (token.name.startsWith('no-')) {
      // Store foo:false for --no-foo
      const positiveName = token.name.slice(3);
      values[positiveName] = false;
      delete values[token.name];
    } else {
      // Resave value so last one wins if both --foo and --no-foo.
      values[token.name] = token.value ?? true;
    }
  });

const color = values.color;
const logfile = values.logfile ?? 'default.log';

console.log({ logfile, color });
```

Example usage showing negated options, and when an option is used
multiple ways then last one wins.

```console
$ node negate.js
{ logfile: 'default.log', color: undefined }
$ node negate.js --no-logfile --no-color
{ logfile: false, color: false }
$ node negate.js --logfile=test.log --color
{ logfile: 'test.log', color: true }
$ node negate.js --no-logfile --logfile=test.log --color --no-color
{ logfile: 'test.log', color: false }
```

-----

<!-- omit in toc -->
## Table of Contents
- [`util.parseArgs([config])`](#utilparseargsconfig)
- [Scope](#scope)
- [Version Matchups](#version-matchups)
- [🚀 Getting Started](#-getting-started)
- [🙌 Contributing](#-contributing)
- [💡 `process.mainArgs` Proposal](#-processmainargs-proposal)
  - [Implementation:](#implementation)
- [📃 Examples](#-examples)
- [F.A.Qs](#faqs)
- [Links & Resources](#links--resources)

-----

## Scope

It is already possible to build great arg parsing modules on top of what Node.js provides; the prickly API is abstracted away by these modules. Thus, process.parseArgs() is not necessarily intended for library authors; it is intended for developers of simple CLI tools, ad-hoc scripts, deployed Node.js applications, and learning materials.

It is exceedingly difficult to provide an API which would both be friendly to these Node.js users while being extensible enough for libraries to build upon. We chose to prioritize these use cases because these are currently not well-served by Node.js' API.

----

## Version Matchups

| Node.js | @pkgjs/parseArgs |
| -- | -- |
| [v18.3.0](https://nodejs.org/docs/latest-v18.x/api/util.html#utilparseargsconfig) | [v0.9.1](https://github.com/pkgjs/parseargs/tree/v0.9.1#utilparseargsconfig) |
| [v16.17.0](https://nodejs.org/dist/latest-v16.x/docs/api/util.html#utilparseargsconfig), [v18.7.0](https://nodejs.org/docs/latest-v18.x/api/util.html#utilparseargsconfig) | [0.10.0](https://github.com/pkgjs/parseargs/tree/v0.10.0#utilparseargsconfig) |

----

## 🚀 Getting Started

1. **Install dependencies.**

   ```bash
   npm install
   ```

2. **Open the index.js file and start editing!**

3. **Test your code by calling parseArgs through our test file**

   ```bash
   npm test
   ```

----

## 🙌 Contributing

Any person who wants to contribute to the initiative is welcome! Please first read the [Contributing Guide](CONTRIBUTING.md)

Additionally, reading the [`Examples w/ Output`](#-examples-w-output) section of this document will be the best way to familiarize yourself with the target expected behavior for parseArgs() once it is fully implemented.

This package was implemented using [tape](https://www.npmjs.com/package/tape) as its test harness.

----

## 💡 `process.mainArgs` Proposal

> Note: This can be moved forward independently of the `util.parseArgs()` proposal/work.

### Implementation:

```javascript
process.mainArgs = process.argv.slice(process._exec ? 1 : 2)
```

----

## 📃 Examples

```js
const { parseArgs } = require('@pkgjs/parseargs');
```

```js
const { parseArgs } = require('@pkgjs/parseargs');
// specify the options that may be used
const options = {
  foo: { type: 'string'},
  bar: { type: 'boolean' },
};
const args = ['--foo=a', '--bar'];
const { values, positionals } = parseArgs({ args, options });
// values = { foo: 'a', bar: true }
// positionals = []
```

```js
const { parseArgs } = require('@pkgjs/parseargs');
// type:string & multiple
const options = {
  foo: {
    type: 'string',
    multiple: true,
  },
};
const args = ['--foo=a', '--foo', 'b'];
const { values, positionals } = parseArgs({ args, options });
// values = { foo: [ 'a', 'b' ] }
// positionals = []
```

```js
const { parseArgs } = require('@pkgjs/parseargs');
// shorts
const options = {
  foo: {
    short: 'f',
    type: 'boolean'
  },
};
const args = ['-f', 'b'];
const { values, positionals } = parseArgs({ args, options, allowPositionals: true });
// values = { foo: true }
// positionals = ['b']
```

```js
const { parseArgs } = require('@pkgjs/parseargs');
// unconfigured
const options = {};
const args = ['-f', '--foo=a', '--bar', 'b'];
const { values, positionals } = parseArgs({ strict: false, args, options, allowPositionals: true });
// values = { f: true, foo: 'a', bar: true }
// positionals = ['b']
```

----

## F.A.Qs

- Is `cmd --foo=bar baz` the same as `cmd baz --foo=bar`?
  - yes
- Does the parser execute a function?
  - no
- Does the parser execute one of several functions, depending on input?
  - no
- Can subcommands take options that are distinct from the main command?
  - no
- Does it output generated help when no options match?
  - no
- Does it generated short usage?  Like: `usage: ls [-ABCFGHLOPRSTUWabcdefghiklmnopqrstuwx1] [file ...]`
  - no (no usage/help at all)
- Does the user provide the long usage text?  For each option?  For the whole command?
  - no
- Do subcommands (if implemented) have their own usage output?
  - no
- Does usage print if the user runs `cmd --help`?
  - no
- Does it set `process.exitCode`?
  - no
- Does usage print to stderr or stdout?
  - N/A
- Does it check types?  (Say, specify that an option is a boolean, number, etc.)
  - no
- Can an option have more than one type?  (string or false, for example)
  - no
- Can the user define a type?  (Say, `type: path` to call `path.resolve()` on the argument.)
  - no
- Does a `--foo=0o22` mean 0, 22, 18, or "0o22"?
  - `"0o22"`
- Does it coerce types?
  - no
- Does `--no-foo` coerce to `--foo=false`?  For all options?  Only boolean options?
  - no, it sets `{values:{'no-foo': true}}`
- Is `--foo` the same as `--foo=true`?  Only for known booleans?  Only at the end?
  - no, they are not the same. There is no special handling of `true` as a value so it is just another string.
- Does it read environment variables?  Ie, is `FOO=1 cmd` the same as `cmd --foo=1`?
  - no
- Do unknown arguments raise an error?  Are they parsed?  Are they treated as positional arguments?
  - no, they are parsed, not treated as positionals
- Does `--` signal the end of options?
  - yes
- Is `--` included as a positional?
  - no
- Is `program -- foo` the same as `program foo`?
  - yes, both store `{positionals:['foo']}`
- Does the API specify whether a `--` was present/relevant?
  - no
- Is `-bar` the same as `--bar`?
  - no, `-bar` is a short option or options, with expansion logic that follows the
    [Utility Syntax Guidelines in POSIX.1-2017](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html). `-bar` expands to `-b`, `-a`, `-r`.
- Is `---foo` the same as `--foo`?
  - no
  - the first is a long option named `'-foo'`
  - the second is a long option named `'foo'`
- Is `-` a positional? ie, `bash some-test.sh | tap -`
  - yes

## Links & Resources

* [Initial Tooling Issue](https://github.com/nodejs/tooling/issues/19)
* [Initial Proposal](https://github.com/nodejs/node/pull/35015)
* [parseArgs Proposal](https://github.com/nodejs/node/pull/42675)

[coverage-image]: https://img.shields.io/nycrc/pkgjs/parseargs
[coverage-url]: https://github.com/pkgjs/parseargs/blob/main/.nycrc
[pkgjs/parseargs]: https://github.com/pkgjs/parseargs