parseArgs

Polyfill of proposal for util.parseArgs()

util.parseArgs([config])

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.
  • 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.

• 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.

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.

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' } []

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' } []ss

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

---

Table of Contents

• util.parseArgs([config])
  • Scope
  • Links & Resources
• 🚀 Getting Started
• 🙌 Contributing
• 💡 process.mainArgs Proposal
  • Implementation:
• 💡 util.parseArgs([config]) Proposal
• 📃 Examples
  • F.A.Qs

---

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.

🚀 Getting Started

1. Install dependencies.

   npm install

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

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

   npm test

---

🙌 Contributing

Any person who wants to contribute to the initiative is welcome! Please first read the Contributing Guide

Additionally, reading the 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 as its test harness.

---

💡 process.mainArgs Proposal

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

Implementation:

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

---

💡 util.parseArgs([config]) Proposal

• config {Object} (Optional) The config parameter is an object supporting the following properties:
  • args {string[]} (Optional) Array of argument strings; defaults to process.mainArgs
  • options {Object} (Optional) An object describing the known options to look for in args; options keys are the long names of the known options, and the values are objects with the following properties:
    • type {'string'|'boolean'} (Required) Type of known option
    • multiple {boolean} (Optional) If true, when appearing one or more times in args, results are collected in an Array
    • short {string} (Optional) A single character alias for an option; When appearing one or more times in args; Respects the multiple configuration
  • strict {Boolean} (Optional) A Boolean for whether or not to throw an error when unknown options are encountered, type:'string' options are missing an options-argument, or type:'boolean' options are passed an options-argument; defaults to true
  • allowPositionals {Boolean} (Optional) Whether this command accepts positional arguments. Defaults false if strict is true, otherwise defaults to true.
• Returns: {Object} An object having properties:
  • values {Object}, key:value for each option found. Value is a string for string options, or true for boolean options, or an array (of strings or booleans) for options configured as multiple:true.
  • positionals {string[]}, containing [Positionals][]

---

📃 Examples

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

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 = []

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 = []

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']

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. -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
• Initial Proposal
• parseArgs Proposal