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parseArgs

Coverage

Polyfill of 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.
      • 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 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.

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' } []

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.

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 });

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.

$ 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 }

Table of Contents

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 v0.9.1
v16.17.0, v18.7.0 0.10.0

🚀 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)

📃 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?
  • 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