cosmiconfig

Cosmiconfig searches for and loads configuration for your program.

It features smart defaults based on conventional expectations in the JavaScript ecosystem. But it's also flexible enough to search wherever you'd like to search, and load whatever you'd like to load.

By default, Cosmiconfig will start where you tell it to start and search up the directory tree for the following:

a package.json property
a JSON or YAML, extensionless "rc file"
an "rc file" with the extensions .json, .yaml, .yml, .js, .ts, .mjs, or .cjs
any of the above two inside a .config subdirectory
a .config.js, .config.ts, .config.mjs, or .config.cjs file

For example, if your module's name is "myapp", cosmiconfig will search up the directory tree for configuration in the following places:

a myapp property in package.json
a .myapprc file in JSON or YAML format
a .myapprc.json, .myapprc.yaml, .myapprc.yml, .myapprc.js, .myapprc.ts, .myapprc.mjs, or .myapprc.cjs file
a myapprc, myapprc.json, myapprc.yaml, myapprc.yml, myapprc.js, myapprc.ts or myapprc.cjs file inside a .config subdirectory
a myapp.config.js, myapp.config.ts, myapp.config.mjs, or myapp.config.cjs file

Cosmiconfig continues to search up the directory tree, checking each of these places in each directory, until it finds some acceptable configuration (or hits the home directory).

Installation
Usage for tooling developers
Result
Asynchronous API
Synchronous API
cosmiconfigOptions
Loading JS modules
Caching
Differences from rc
Usage for end users
Contributing & Development

Installation

npm install cosmiconfig

Tested in Node 14+.

Usage for tooling developers

If you are an end user (i.e. a user of a tool that uses cosmiconfig, like prettier or stylelint), you can skip down to the end user section.

Create a Cosmiconfig explorer, then either search for or directly load a configuration file.

const { cosmiconfig, cosmiconfigSync } = require('cosmiconfig');
// ...
const explorer = cosmiconfig(moduleName);

// Search for a configuration by walking up directories.
// See documentation for search, below.
explorer.search()
  .then((result) => {
    // result.config is the parsed configuration object.
    // result.filepath is the path to the config file that was found.
    // result.isEmpty is true if there was nothing to parse in the config file.
  })
  .catch((error) => {
    // Do something constructive.
  });

// Load a configuration directly when you know where it should be.
// The result object is the same as for search.
// See documentation for load, below.
explorer.load(pathToConfig).then(..);

// You can also search and load synchronously.
const explorerSync = cosmiconfigSync(moduleName);

const searchedFor = explorerSync.search();
const loaded = explorerSync.load(pathToConfig);

Result

The result object you get from search or load has the following properties:

config: The parsed configuration object. undefined if the file is empty.
filepath: The path to the configuration file that was found.
isEmpty: true if the configuration file is empty. This property will not be present if the configuration file is not empty.

Asynchronous API

cosmiconfig()

const { cosmiconfig } = require('cosmiconfig');
const explorer = cosmiconfig(moduleName[, cosmiconfigOptions])

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

moduleName

Type: string. Required.

Your module name. This is used to create the default searchPlaces and packageProp.

If your searchPlaces value will include files, as it does by default (e.g. ${moduleName}rc), your moduleName must consist of characters allowed in filenames. That means you should not copy scoped package names, such as @my-org/my-package, directly into moduleName.

cosmiconfigOptions are documented below. You may not need them, and should first read about the functions you'll use.

explorer.search()

explorer.search([searchFrom]).then(result => {..})

Searches for a configuration file. Returns a Promise that resolves with a result or with null, if no configuration file is found.

You can do the same thing synchronously with explorerSync.search().

Let's say your module name is goldengrahams so you initialized with const explorer = cosmiconfig('goldengrahams');. Here's how your default search() will work:

Starting from process.cwd() (or some other directory defined by the searchFrom argument to search()), look for configuration objects in the following places:
1. A goldengrahams property in a package.json file.
2. A .goldengrahamsrc file with JSON or YAML syntax.
3. A .goldengrahamsrc.json, .goldengrahamsrc.yaml, .goldengrahamsrc.yml, .goldengrahamsrc.js, .goldengrahamsrc.ts, or .goldengrahamsrc.cjs file. (To learn more about how JS files are loaded, see "Loading JS modules".)
4. A goldengrahamsrc, goldengrahamsrc.json, goldengrahamsrc.yaml, goldengrahamsrc.yml, goldengrahamsrc.js, goldengrahamsrc.ts, or goldengrahamsrc.cjs file in the .config subdirectory.
5. A goldengrahams.config.js, goldengrahams.config.ts, goldengrahams.config.mjs, or goldengrahams.config.cjs file. (To learn more about how JS files are loaded, see "Loading JS modules".)
If none of those searches reveal a configuration object, move up one directory level and try again. So the search continues in ./, ../, ../../, ../../../, etc., checking the same places in each directory.
Continue searching until arriving at your home directory (or some other directory defined by the cosmiconfig option stopDir).
For JS files,
If at any point a parsable configuration is found, the search() Promise resolves with its result (or, with explorerSync.search(), the result is returned).
If no configuration object is found, the search() Promise resolves with null (or, with explorerSync.search(), null is returned).
If a configuration object is found but is malformed (causing a parsing error), the search() Promise rejects with that error (so you should .catch() it). (Or, with explorerSync.search(), the error is thrown.)

If you know exactly where your configuration file should be, you can use load(), instead.

The search process is highly customizable. Use the cosmiconfig options searchPlaces and loaders to precisely define where you want to look for configurations and how you want to load them.

searchFrom

Type: string. Default: process.cwd().

A filename. search() will start its search here.

If the value is a directory, that's where the search starts. If it's a file, the search starts in that file's directory.

explorer.load()

explorer.load(loadPath).then(result => {..})

Loads a configuration file. Returns a Promise that resolves with a result or rejects with an error (if the file does not exist or cannot be loaded).

Use load if you already know where the configuration file is and you just need to load it.

explorer.load('load/this/file.json'); // Tries to load load/this/file.json.

If you load a package.json file, the result will be derived from whatever property is specified as your packageProp.

You can do the same thing synchronously with explorerSync.load().

explorer.clearLoadCache()

Clears the cache used in load().

explorer.clearSearchCache()

Clears the cache used in search().

explorer.clearCaches()

Performs both clearLoadCache() and clearSearchCache().

Synchronous API

cosmiconfigSync()

const { cosmiconfigSync } = require('cosmiconfig');
const explorerSync = cosmiconfigSync(moduleName[, cosmiconfigOptions])

Creates a synchronous cosmiconfig instance ("explorerSync") configured according to the arguments, and initializes its caches.

See cosmiconfig().

explorerSync.search()

const result = explorerSync.search([searchFrom]);

Synchronous version of explorer.search().

Returns a result or null.

explorerSync.load()

const result = explorerSync.load(loadPath);

Synchronous version of explorer.load().

Returns a result.

explorerSync.clearLoadCache()

Clears the cache used in load().

explorerSync.clearSearchCache()

Clears the cache used in search().

explorerSync.clearCaches()

Performs both clearLoadCache() and clearSearchCache().

cosmiconfigOptions

Type: Object.

Possible options are documented below.

searchPlaces

Type: Array<string>. Default: See below.

An array of places that search() will check in each directory as it moves up the directory tree. Each place is relative to the directory being searched, and the places are checked in the specified order.

Default searchPlaces:

For the asynchronous API, these are the default searchPlaces:

[
  'package.json',
  `.${moduleName}rc`,
  `.${moduleName}rc.json`,
  `.${moduleName}rc.yaml`,
  `.${moduleName}rc.yml`,
  `.${moduleName}rc.js`,
  `.${moduleName}rc.ts`,
  `.${moduleName}rc.mjs`,
  `.${moduleName}rc.cjs`,
  `.config/${moduleName}rc`,
  `.config/${moduleName}rc.json`,
  `.config/${moduleName}rc.yaml`,
  `.config/${moduleName}rc.yml`,
  `.config/${moduleName}rc.js`,
  `.config/${moduleName}rc.ts`,
  `.config/${moduleName}rc.cjs`,
  `${moduleName}.config.js`,
  `${moduleName}.config.ts`,
  `${moduleName}.config.mjs`,
  `${moduleName}.config.cjs`,
];

For the synchronous API, the only difference is that .mjs files are not included. See "Loading JS modules" for more information.

Create your own array to search more, fewer, or altogether different places.

Every item in searchPlaces needs to have a loader in loaders that corresponds to its extension. (Common extensions are covered by default loaders.) Read more about loaders below.

package.json is a special value: When it is included in searchPlaces, Cosmiconfig will always parse it as JSON and load a property within it, not the whole file. That property is defined with the packageProp option, and defaults to your module name.

Examples, with a module named porgy:

// Disallow extensions on rc files:
['package.json', '.porgyrc', 'porgy.config.js'][
  // Limit the options dramatically:
  ('package.json', '.porgyrc')
][
  // Maybe you want to look for a wide variety of JS flavors:
  ('porgy.config.js',
  'porgy.config.mjs',
  'porgy.config.ts',
  'porgy.config.coffee')
][
  // ^^ You will need to designate custom loaders to tell
  // Cosmiconfig how to handle `.ts` and `.coffee` files.

  // Look within a .config/ subdirectory of every searched directory:
  ('package.json',
  '.porgyrc',
  '.config/.porgyrc',
  '.porgyrc.json',
  '.config/.porgyrc.json')
];

loaders

Type: Object. Default: See below.

An object that maps extensions to the loader functions responsible for loading and parsing files with those extensions.

Cosmiconfig exposes its default loaders on the named export defaultLoaders and defaultLoadersSync.

Default loaders:

const { defaultLoaders, defaultLoadersSync } = require('cosmiconfig');

console.log(Object.entries(defaultLoaders));
// [
//   [ '.mjs', [Function: loadJs] ],
//   [ '.cjs', [Function: loadJs] ],
//   [ '.js', [Function: loadJs] ],
//   [ '.ts', [Function: loadTs] ],
//   [ '.json', [Function: loadJson] ],
//   [ '.yaml', [Function: loadYaml] ],
//   [ '.yml', [Function: loadYaml] ],
//   [ 'noExt', [Function: loadYaml] ]
// ]

console.log(Object.entries(defaultLoadersSync));
// [
//   [ '.cjs', [Function: loadJsSync] ],
//   [ '.js', [Function: loadJsSync] ],
//   [ '.ts', [Function: loadTsSync] ],
//   [ '.json', [Function: loadJson] ],
//   [ '.yaml', [Function: loadYaml] ],
//   [ '.yml', [Function: loadYaml] ],
//   [ 'noExt', [Function: loadYaml] ]
// ]

(YAML is a superset of JSON; which means YAML parsers can parse JSON; which is how extensionless files can be either YAML or JSON with only one parser.)

If you provide a loaders object, your object will be merged with the defaults. So you can override one or two without having to override them all.

Keys in loaders are extensions (starting with a period), or noExt to specify the loader for files without extensions, like .myapprc.

Values in loaders are a loader function (described below) whose values are loader functions.

The most common use case for custom loaders value is to load extensionless rc files as strict JSON, instead of JSON or YAML (the default). To accomplish that, provide the following loaders value:

{
  noExt: defaultLoaders['.json'];
}

If you want to load files that are not handled by the loader functions Cosmiconfig exposes, you can write a custom loader function or use one from NPM if it exists.

Third-party loaders:

cosmiconfig-typescript-loader

Use cases for custom loader function:

Allow configuration syntaxes that aren't handled by Cosmiconfig's defaults, like JSON5, INI, or XML.
Allow ES2015 modules from .mjs configuration files.
Parse JS files with Babel before deriving the configuration.

Custom loader functions have the following signature:

// Sync
(filepath: string, content: string) => Object | null

// Async
(filepath: string, content: string) => Object | null | Promise<Object | null>

Cosmiconfig reads the file when it checks whether the file exists, so it will provide you with both the file's path and its content. Do whatever you need to, and return either a configuration object or null (or, for async-only loaders, a Promise that resolves with one of those). null indicates that no real configuration was found and the search should continue.

A few things to note:

If you use a custom loader, be aware of whether it's sync or async: you cannot use async customer loaders with the sync API (cosmiconfigSync()).
Special JS syntax can also be handled by using a require hook, because defaultLoaders['.js'] just uses require. Whether you use custom loaders or a require hook is up to you.

Examples:

// Allow JSON5 syntax:
{
  '.json': json5Loader
}

// Allow a special configuration syntax of your own creation:
{
  '.special': specialLoader
}

// Allow many flavors of JS, using custom loaders:
{
  '.coffee': coffeeScriptLoader
}

// Allow many flavors of JS but rely on require hooks:
{
  '.coffee': defaultLoaders['.js']
}

packageProp

Type: string | Array<string>. Default: `${moduleName}`.

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

Use a period-delimited string or an array of strings to describe a path to nested properties.

For example, the value 'configs.myPackage' or ['configs', 'myPackage'] will get you the "myPackage" value in a package.json like this:

{
  "configs": {
    "myPackage": {..}
  }
}

If nested property names within the path include periods, you need to use an array of strings. For example, the value ['configs', 'foo.bar', 'baz'] will get you the "baz" value in a package.json like this:

{
  "configs": {
    "foo.bar": {
      "baz": {..}
    }
  }
}

If a string includes period but corresponds to a top-level property name, it will not be interpreted as a period-delimited path. For example, the value 'one.two' will get you the "three" value in a package.json like this:

{
  "one.two": "three",
  "one": {
    "two": "four"
  }
}

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. Read more about "Caching" below.

transform

Type: (Result) => Promise<Result> | Result.

A function that transforms the parsed configuration. Receives the result.

If using search() or load() (which are async), the transform function can return the transformed result or return a Promise that resolves with the transformed result. If using cosmiconfigSync, search() or load(), the function must be synchronous and return 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 searched or loaded.

ignoreEmptySearchPlaces

Type: boolean. Default: true.

By default, if search() encounters an empty file (containing nothing but whitespace) in one of the searchPlaces, it will ignore the empty file and move on. If you'd like to load empty configuration files, instead, set this option to false.

Why might you want to load empty configuration files? If you want to throw an error, or if an empty configuration file means something to your program.

Loading JS modules

Your end users can provide JS configuration files as ECMAScript modules (ESM) under the following conditions:

You (the cosmiconfig user) use cosmiconfig's asynchronous API.
Your end user runs a version of Node that supports ESM (>=12.17.0, or earlier with the --experimental-modules flag).
Your end user provides an .mjs configuration file, or a .js file whose nearest parent package.json file contains "type": "module". (See Node's method for determining a file's module system.)

With cosmiconfig's asynchronous API, the default searchPlaces include .js, .ts, .mjs, and .cjs files. Cosmiconfig loads all these file types with the dynamic import function.

With the synchronous API, JS configuration files are always treated as CommonJS, and .mjs files are ignored, because there is no synchronous API for the dynamic import function.

Caching

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

To avoid or work around caching, you can do the following:

Set the cosmiconfig option cache to false.
Use the cache-clearing methods clearLoadCache(), clearSearchCache(), and clearCaches().
Create separate instances of cosmiconfig (separate "explorers").

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).

Usage for end users

When configuring a tool, you can use multiple file formats and put these in multiple places.

Usually, a tool would mention this in its own README file, but by default, these are the following places, where {NAME} represents the name of the tool:

package.json
.{NAME}rc
.{NAME}rc.json
.{NAME}rc.yaml
.{NAME}rc.yml
.{NAME}rc.js
.{NAME}rc.ts
.{NAME}rc.cjs
.config/{NAME}rc
.config/{NAME}rc.json
.config/{NAME}rc.yaml
.config/{NAME}rc.yml
.config/{NAME}rc.js
.config/{NAME}rc.ts
.config/{NAME}rc.cjs
{NAME}.config.js
{NAME}.config.ts
{NAME}.config.cjs

The contents of these files are defined by the tool. For example, you can configure prettier to enforce semicolons at the end of the line using a file named .config/prettierrc.yml:

semi: true

Additionally, you have the option to put a property named after the tool in your package.json file, with the contents of that property being the same as the file contents. To use the same example as above:

{
  "name": "your-project",
  "dependencies": {},
  "prettier": {
    "semi": true
  }
}

This has the advantage that you can put the configuration of all tools (at least the ones that use cosmiconfig) in one file.

You can also add a cosmiconfig key within your package.json file or create one of the following files to configure cosmiconfig itself:

.config.json
.config.yaml
.config.yml
.config.js
.config.ts
.config.cjs

The following property is currently actively supported in these places:

cosmiconfig:
  # overrides where configuration files are being searched to enforce a custom naming convention and format
  searchPlaces:
    - .config/{name}.yml

Note: technically, you can overwrite all options described in cosmiconfigOptions here, but everything not listed above should be used at your own risk, as it has not been tested explicitly.

You can also add more root properties outside the cosmiconfig property to configure your tools, entirely eliminating the need to look for additional configuration files:

cosmiconfig:
  searchPlaces: []

prettier:
  semi: true

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!

GavinMeierSonos/cosmiconfig