cosmiconfig

What is cosmiconfig?

The cosmiconfig npm package is a utility for finding and loading configuration from a variety of file formats and locations. It is commonly used in Node.js projects to create flexible configuration systems for tools and libraries.

What are cosmiconfig's main functionalities?

Searching for configuration files

This feature allows you to search for configuration files with a given name in various locations, including package.json properties, rc files, and regular JSON or YAML files.

const cosmiconfig = require('cosmiconfig');
const explorer = cosmiconfig('yourModuleName');
explorer.search()
  .then((result) => {
    const config = result ? result.config : {};
    // do something with config
  })
  .catch((error) => {
    // handle error
  });

Loading configuration files directly

This feature allows you to load a configuration file directly from a specified path, regardless of the file's format.

const cosmiconfig = require('cosmiconfig');
const explorer = cosmiconfig('yourModuleName');
explorer.load('/path/to/config').then((result) => {
  const config = result ? result.config : {};
  // do something with config
}).catch((error) => {
  // handle error
});

Creating a custom explorer

This feature allows you to create a custom explorer with specific search places and loaders, enabling you to define where and how configuration files should be found and interpreted.

const cosmiconfig = require('cosmiconfig');
const explorer = cosmiconfig('yourModuleName', {
  searchPlaces: ['custom.config.js', 'package.json'],
  loaders: {
    '.js': cosmiconfig.loadJs,
    '.json': cosmiconfig.loadJson
  }
});

Other packages similar to cosmiconfig

rc

The 'rc' package is similar to cosmiconfig in that it also searches for and loads configuration files. However, 'rc' focuses on a specific pattern of '.rc' files and does not support as many file formats as cosmiconfig.

config

The 'config' package is another configuration loader that supports multiple file formats. Unlike cosmiconfig, 'config' is designed for application configuration and has a different approach to file discovery, defaulting to a 'config' directory.

convict

Convict is a configuration management library that includes schema definitions. It is more opinionated than cosmiconfig and includes validation and environment variable support out of the box, which cosmiconfig does not do without additional setup.

README

cosmiconfig

Find and load a configuration object from

• a package.json property (anywhere up the directory tree)
• a JSON or YAML "rc file" (anywhere up the directory tree)
• a .config.js CommonJS module (anywhere up the directory tree)

For example, if your module's name is "soursocks," cosmiconfig will search out configuration in the following places:

• a soursocks property in package.json (anywhere up the directory tree)
• a .soursocksrc file in JSON or YAML format (anywhere up the directory tree)
• a soursocks.config.js file exporting a JS object (anywhere up the directory tree)

cosmiconfig continues to search in these places all the way up the directory tree until it finds acceptable configuration (or hits the home directory).

Additionally, all of these search locations are configurable: you can customize filenames or turn off any location.

You can also look for rc files with extensions, e.g. .soursocksrc.json or .soursocksrc.yaml. You may like extensions on your rc files because you'll get syntax highlighting and linting in text editors.

Installation

npm install cosmiconfig

Tested in Node 4+.

Usage

var cosmiconfig = require('cosmiconfig');

var explorer = cosmiconfig(yourModuleName[, options]);

explorer.load(yourSearchPath)
  .then((result) => {
    // result.config is the parsed configuration object
    // result.filepath is the path to the config file that was found
  })
  .catch((parsingError) => {
    // do something constructive
  });

The function cosmiconfig() searches for a configuration object and returns a Promise, which resolves with an object containing the information you're looking for.

You can also pass option sync: true to load the config synchronously, returning the config itself.

So let's say var yourModuleName = 'goldengrahams' — here's how cosmiconfig will work:

• Starting from process.cwd() (or some other directory defined by the searchPath argument to load()), it looks for configuration objects in three places, in this order:
  1. A goldengrahams property in a package.json file (or some other property defined by options.packageProp);
  2. A .goldengrahamsrc file with JSON or YAML syntax (or some other filename defined by options.rc);
  3. A goldengrahams.config.js JS file exporting the object (or some other filename defined by options.js).
• If none of those searches reveal a configuration object, it moves up one directory level and tries again. So the search continues in ./, ../, ../../, ../../../, etc., checking those three locations in each directory.
• It continues searching until it arrives at your home directory (or some other directory defined by options.stopDir).
• If at any point a parseable configuration is found, the cosmiconfig() Promise resolves with its result object.
• If no configuration object is found, the cosmiconfig() Promise resolves with null.
• If a configuration object is found but is malformed (causing a parsing error), the cosmiconfig() Promise rejects and shares that error (so you should .catch() it).

All this searching can be short-circuited by passing options.configPath to specify a file. cosmiconfig will read that file and try parsing it as JSON, YAML, or JS.

Caching

As of v2, cosmiconfig uses a few caches to reduce the need for repetitious reading of the filesystem. Every new cosmiconfig instance (created with cosmiconfig()) has its own caches.

To avoid or work around caching, you can

• create separate instances of cosmiconfig, or
• set cache: false in your options.
• use the cache clearing methods documented below.

API

var explorer = cosmiconfig(moduleName[, options])

Creates a cosmiconfig instance (i.e. explorer) configured according to the arguments, and initializes its caches.

moduleName

Type: string

You module name. This is used to create the default filenames that cosmiconfig will look for.

Options

packageProp

Type: string or false Default: '[moduleName]'

Name of the property in package.json to look for.

If false, cosmiconfig will not look in package.json files.

rc

Type: string or false Default: '.[moduleName]rc'

Name of the "rc file" to look for, which can be formatted as JSON or YAML.

If false, cosmiconfig will not look for an rc file.

If rcExtensions: true, the rc file can also have extensions that specify the syntax, e.g. .[moduleName]rc.json. You may like extensions on your rc files because you'll get syntax highlighting and linting in text editors. Also, with rcExtensions: true, you can use JS modules as rc files, e.g. .[moduleName]rc.js.

js

Type: string or false Default: '[moduleName].config.js'

Name of a JS file to look for, which must export the configuration object.

If false, cosmiconfig will not look for a JS file.

rcStrictJson

Type: boolean Default: false

If true, cosmiconfig will expect rc files to be strict JSON. No YAML permitted, and no sloppy JSON.

By default, rc files are parsed with js-yaml, which is more permissive with punctuation than standard strict JSON.

rcExtensions

Type: boolean Default: false

If true, cosmiconfig will look for rc files with extensions, in addition to rc files without.

This adds a few steps to the search process. Instead of just looking for .goldengrahamsrc (no extension), it will also look for the following, in this order:

• .goldengrahamsrc.json
• .goldengrahamsrc.yaml
• .goldengrahamsrc.yml
• .goldengrahamsrc.js

stopDir

Type: string Default: Absolute path to your home directory

Directory where the search will stop.

cache

Type: boolean Default: true

If false, no caches will be used.

sync

Type: boolean Default: false

If true, config will be loaded synchronously.

transform

Type: Function

A function that transforms the parsed configuration. Receives the result object with config and filepath properties.

If the option sync is false (default), the function must return a Promise that resolves with the transformed result. If the option sync is true, though, transform should be a synchronous function which returns the transformed result.

The reason you might use this option instead of simply applying your transform function some other way is that the transformed result will be cached. If your transformation involves additional filesystem I/O or other potentially slow processing, you can use this option to avoid repeating those steps every time a given configuration is loaded.

configPath

Type: string

If provided, cosmiconfig will load and parse a config from this path, and will not perform its usual search.

format

Type: 'json' | 'yaml' | 'js'

The expected file format for the config loaded from configPath.

If not specified, cosmiconfig will try to infer the format using the extension name (if it has one). In the event that the file does not have an extension or the extension is unrecognized, cosmiconfig will try to parse it as a JSON, YAML, or JS file.

Instance methods (on explorer)

load([searchPath, configPath])

Find and load a configuration file. Returns a Promise that resolves with null, if nothing is found, or an object with two properties:

• config: The loaded and parsed configuration.
• filepath: The filepath where this configuration was found.

You should provide either searchPath or configPath. Use configPath if you know the path of the configuration file you want to load. Otherwise, use searchPath.

explorer.load('start/search/here');
explorer.load('start/search/at/this/file.css');

explorer.load(null, 'load/this/file.json');

If you provide searchPath, cosmiconfig will start its search at searchPath and continue to search up the directory tree, as documented above.

If you provide configPath (i.e. you already know where the configuration is that you want to load), cosmiconfig will try to read and parse that file. Note that the format option is applicable for this as well.

clearFileCache()

Clears the cache used when you provide a configPath argument to load.

clearDirectoryCache()

Clears the cache used when you provide a searchPath argument to load.

clearCaches()

Performs both clearFileCache() and clearDirectoryCache().

Differences from rc

rc serves its focused purpose well. cosmiconfig differs in a few key ways — making it more useful for some projects, less useful for others:

• Looks for configuration in some different places: in a package.json property, an rc file, a .config.js file, and rc files with extensions.
• Built-in support for JSON, YAML, and CommonJS formats.
• Stops at the first configuration found, instead of finding all that can be found up the directory tree and merging them automatically.
• Options.
• Asynchronous by default (though can be run synchronously).

Contributing & Development

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

And please do participate!

Changelog

3.1.0

• Added: infer format based on filePath