meow

library0.4.2jsnpmunverified

Meow is a minimalist and dependency-free helper library designed for creating command-line interface (CLI) applications in Node.js. It simplifies argument parsing, flag handling, and generation of help and version output. Currently stable at version 14.1.0, Meow maintains an active release cadence, often aligning major versions with Node.js LTS releases to keep up with runtime changes. Its key differentiators include automatic conversion of flags to camelCase, support for `--no-` prefix flag negation, and built-in `--version` and `--help` handling. Since version 12, Meow has been ESM-only, requiring modern Node.js module syntax and an `import.meta` object for package metadata resolution. Recent additions include robust subcommand parsing via the `commands` option and the ability to make input arguments required. It's an opinionated, lightweight choice for CLI parsing.

devops

npm install meow

github ↗package ↗

INSTALL

IMPORT

SIG · MEOW

meow

devopsjavascriptv0.4.2

Install

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Import

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Disk

—

Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

meow

✓ import meow from 'meow';

✗ const meow = require('meow');

`meow` is an ESM-only package since v12. Using `require()` will result in an `ERR_REQUIRE_ESM` error. Your project must be configured for ESM.

AnyFlag

✓ import type { AnyFlag } from 'meow';

Imports the TypeScript type for a single flag definition. Often used with generics for stricter type checking.

AnyFlags

✓ import type { AnyFlags } from 'meow';

Imports the TypeScript type for the entire flags object. Useful for type-checking the `cli.flags` return value.

This example demonstrates basic CLI setup with `meow`, parsing a main input argument and a boolean flag, and printing a message. It includes the mandatory `import.meta` option.

#!/usr/bin/env node import meow from 'meow'; const cli = meow(` Usage $ foo <input> Options --rainbow, -r Include a rainbow Examples $ foo unicorns --rainbow 🌈 unicorns 🌈 `, { importMeta: import.meta, // This is required for meow to find package.json flags: { rainbow: { type: 'boolean', shortFlag: 'r' } } }); // Example usage with parsed input and flags const inputArgument = cli.input.at(0); const enableRainbow = cli.flags.rainbow; if (inputArgument) { const message = enableRainbow ? `🌈 ${inputArgument} 🌈` : inputArgument; console.log(message); } else { console.log('No input provided. Try: foo unicorns --rainbow'); cli.showHelp(); }

meow --version

Debug

Known issues

breakingMeow v14 and later require Node.js 20 or newer. Earlier versions of Node.js are no longer supported.

fix

Upgrade your Node.js environment to version 20 or higher. Consider using a Node.js version manager (e.g., `nvm` or `volta`) to manage different project requirements.

affects: >=14.0.0

breakingMeow is an ECMAScript Module (ESM) only package since v12. Attempting to use `require()` will result in a runtime error (`ERR_REQUIRE_ESM`).

fix

Migrate your project to use ESM syntax (`import`/`export`) and ensure your `package.json` includes `"type": "module"`. For TypeScript, configure `"module": "node16"` or `"nodenext"` in `tsconfig.json`.

affects: >=12.0.0

breakingThe `alias` flag option was renamed to `shortFlag` in v12 to provide more precise terminology. A separate `aliases` option is now available for actual multi-character aliases.

fix

Update flag definitions from `alias: 'x'` to `shortFlag: 'x'` in your `meow` configuration. If you intended to have multiple aliases, use the new `aliases` option.

affects: >=12.0.0

breakingThe `importMeta` option is now a required configuration property for the `meow` constructor (since v12). It is used to correctly locate the `package.json` for version and help information.

fix

Always pass `{ importMeta: import.meta }` to the `meow` constructor when initializing your CLI application.

affects: >=12.0.0

gotchaThe `hardRejection` option was removed in v13.1.0 because its functionality became the default behavior for unhandled promise rejections in Node.js 16 and later.

fix

Remove the `hardRejection` option from your `meow` configuration. No functional changes are expected if your Node.js version is 16 or newer.

affects: >=13.1.0

Errors

Common errors & fixes

ERR_REQUIRE_ESM: require() of ES Module .../node_modules/meow/index.js from ... not supported.

Attempting to import `meow` using CommonJS `require()` syntax in an ES Module context, or in a CommonJS project that doesn't correctly handle ESM imports.

fix

Refactor your application to use ES Modules (`import meow from 'meow';`) and ensure your `package.json` has `"type": "module"`. If using TypeScript, set `"module": "node16"` or `"nodenext"` and `"moduleResolution": "node16"` or `"nodenext"` in `tsconfig.json`.

Error: The `importMeta` option is required.

The `importMeta: import.meta` option was omitted from the `meow` constructor call.

fix

Add `{ importMeta: import.meta }` to the `meow` constructor. This property is crucial for `meow` to correctly resolve paths to your `package.json` for displaying help and version information.

Error [ERR_OS_NOT_SUPPORTED]: Your current Node.js version is X.Y.Z, but meow requires >=20. The latest Node.js LTS version is recommended.

The installed Node.js version does not meet the minimum requirement specified by `meow`.

fix

Upgrade your Node.js environment to version 20 or higher. You can use tools like `nvm install 20` or `volta install node@20`.

TypeError: 'alias' is not a valid flag option. Did you mean 'shortFlag'?

An older `meow` configuration or code attempting to use the `alias` property within flag definitions after `meow` v12, where it was renamed.

fix

Replace the `alias` property with `shortFlag` in your flag definitions (e.g., `shortFlag: 'r'` instead of `alias: 'r'`). If you need multiple aliases, use the new `aliases` option.

Error: Input required.

The `input.isRequired` option is set to `true` in the `meow` configuration, but no non-flag arguments were provided when running the CLI.

fix

Ensure that the necessary input arguments are always provided to the CLI. If the input is not strictly mandatory in all scenarios, consider setting `input.isRequired: false` or making it a function that dynamically determines requirement.

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Version history

0.4.2latest on npm

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Dependencies

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Agent activity

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Resources

githubhttps://github.com/sindresorhus/meow ↗

packagehttps://www.npmjs.com/package/meow ↗