cosmiconfig
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 check the current directory for the following:
- a
package.jsonproperty - 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
.configsubdirectory - a
.config.js,.config.ts,.config.mjs, or.config.cjsfile
For example, if your module's name is "myapp", cosmiconfig will search up the directory tree for configuration in the following places:
- a
myappproperty inpackage.json - a
.myapprcfile in JSON or YAML format - a
.myapprc.json,.myapprc.yaml,.myapprc.yml,.myapprc.js,.myapprc.ts,.myapprc.mjs, or.myapprc.cjsfile - a
myapprc,myapprc.json,myapprc.yaml,myapprc.yml,myapprc.js,myapprc.ts,myapprc.mjs, ormyapprc.cjsfile inside a.configsubdirectory - a
myapp.config.js,myapp.config.ts,myapp.config.mjs, ormyapp.config.cjsfile
Optionally, you can tell it to search up the directory tree using search strategies, checking each of these places in each directory, until it finds some acceptable configuration (or hits the home directory).
Table of contents
- 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 cosmiconfigTested 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.
undefinedif the file is empty. - filepath: The path to the configuration file that was found.
- isEmpty:
trueif 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, /* optional */ 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 thesearchFromargument tosearch()), look for configuration objects in the following places:- A
goldengrahamsproperty in apackage.jsonfile. - A
.goldengrahamsrcfile with JSON or YAML syntax. - A
.goldengrahamsrc.json,.goldengrahamsrc.yaml,.goldengrahamsrc.yml,.goldengrahamsrc.js,.goldengrahamsrc.ts,.goldengrahamsrc.mjs, or.goldengrahamsrc.cjsfile. (To learn more about how JS files are loaded, see "Loading JS modules".) - A
goldengrahamsrc,goldengrahamsrc.json,goldengrahamsrc.yaml,goldengrahamsrc.yml,goldengrahamsrc.js,goldengrahamsrc.ts,goldengrahamsrc.mjs, orgoldengrahamsrc.cjsfile in the.configsubdirectory. - A
goldengrahams.config.js,goldengrahams.config.ts,goldengrahams.config.mjs, orgoldengrahams.config.cjsfile. (To learn more about how JS files are loaded, see "Loading JS modules".)
- A
- If none of those searches reveal a configuration object, continue depending on the current search strategy:
- If it's
none(which is the default if you don't specify astopDiroption), stop here and return/resolve withnull. - If it's
global(which is the default if you specify astopDiroption), move up one directory level and try again, recursing until arriving at the configuredstopDiroption, which defaults to the user's home directory.- After arriving at the
stopDir, the global configuration directory (as defined byenv-pathswithout prefix) is also checked, looking at the filesconfig,config.json,config.yaml,config.yml,config.js,config.ts,config.cjs, andconfig.mjsin the directory~/.config/goldengrahams/(on Linux; seeenv-pathsdocumentation for other OSs).
- After arriving at the
- If it's
project, check whether apackage.jsonfile is present in the current directory, and if not, move up one directory level and try again, recursing until there is one.
- If it's
- If at any point a parsable configuration is found, the
search()Promise resolves with its result (or, withexplorerSync.search(), the result is returned). - If no configuration object is found, the
search()Promise resolves withnull(or, withexplorerSync.search(),nullis 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, withexplorerSync.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.
package.yaml will work as well if you specify these file names in your searchPlaces.
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, /* optional */ 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.
searchStrategy
Type: string
Default: global if stopDir is specified, none otherwise.
The strategy that should be used to determine which directories to check for configuration files.
none: Only checks in the current working directory.project: Starts in the current working directory, traversing upwards until apackage.{json,yaml}file is found.global: Starts in the current working directory, traversing upwards until the configuredstopDir(or the current user's home directory if none is given). Then, if no configuration is found, also look in the operating system's default configuration directory (according toenv-pathswithout prefix), where a different set of file names is checked:
[
`config`,
`config.json`,
`config.yaml`,
`config.yml`,
`config.js`,
`config.ts`,
`config.cjs`,
`config.mjs`
]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.mjs`,
`.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.
package.yaml (used by pnpm) works the same way.
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 a custom loader to tell
// Cosmiconfig how to handle `.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.
Use cases for custom loader function:
- Allow configuration syntaxes that aren't handled by Cosmiconfig's defaults, like JSON5, INI, or XML.
- Parse JS files with Babel before deriving the configuration.
Custom loader functions have the following signature:
// Sync
type SyncLoader = (filepath: string, content: string) => Object | null
// Async
type AsyncLoader = (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
requirehook, becausedefaultLoaders['.js']just usesrequire. Whether you use custom loaders or arequirehook is up to you.
Examples:
// Allow JSON5 syntax:
cosmiconfig('foo', {
loaders: {
'.json': json5Loader
}
});
// Allow a special configuration syntax of your own creation:
cosmiconfig('foo', {
loaders: {
'.special': specialLoader
}
});
// Allow many flavors of JS, using custom loaders:
cosmiconfig('foo', {
loaders: {
'.coffee': coffeeScriptLoader
}
});
// Allow many flavors of JS but rely on require hooks:
cosmiconfig('foo', {
loaders: {
'.coffee': defaultLoaders['.js']
}
});packageProp
Type: string | Array<string>.
Default: `${moduleName}`.
Name of the property in package.json (or package.yaml) 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": {"option": "value"}
}
}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": {"option": "value"}
}
}
}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-modulesflag). - Your end user provides an
.mjsconfiguration file, or a.jsfile whose nearest parentpackage.jsonfile 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
cosmiconfigoptioncachetofalse. - Use the cache-clearing methods
clearLoadCache(),clearSearchCache(), andclearCaches(). - 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.jsonproperty, an rc file, a.config.jsfile, 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.mjs
.config/{NAME}rc.cjs
{NAME}.config.js
{NAME}.config.ts
{NAME}.config.mjs
{NAME}.config.cjsThe 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: trueAdditionally, 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/config.json
.config/config.yaml
.config/config.yml
.config/config.js
.config/config.ts
.config/config.cjsThe following properties are currently actively supported in these places:
cosmiconfig:
# adds places where configuration files are being searched
searchPlaces:
- .config/{name}.yml
# to enforce a custom naming convention and format, don't merge the above with the tool-defined search places
# (`true` is the default setting)
mergeSearchPlaces: falseNote: 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. The only exceptions to this are the
loadersproperty, which is explicitly not supported at this time, and thesearchStrategyproperty, which is intentionally disallowed.
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: trueImports
Wherever you put your configuration (the package.json file, a root config file or a package-specific config file),
you can use the special $import key to import another file as a base.
For example, you can import from an npm package (in this example, @foocorp/config).
.prettierrc.base.yml in said npm package could define some company-wide defaults:
printWidth: 120
semi: true
tabWidth: 2And then, the .prettierrc.yml file in the project itself would just reference that file,
optionally overriding the defaults with project-specific settings:
$import: node_modules/@foocorp/config/.prettierrc.base.yml
# we want more space!
printWidth: 200It is possible to import multiple base files by specifying an array of paths, which will be processed in declaration order; that means that the last entry will win if there are conflicting properties.
It is also possible to import file formats other than the importing format as long as they are supported by the loaders specified by the developer of the tool you're configuring.
$import: [first.yml, second.json, third.config.js]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!