# c12

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> Smart Configuration Loader

## Features

- JSON, CJS, Typescript, and ESM config loader with [unjs/jiti](https://github.com/unjs/jiti)
- RC config support with [unjs/rc9](https://github.com/unjs/rc9)
- Multiple sources merged with [unjs/defu](https://github.com/unjs/defu)
- `.env` support with [dotenv](https://www.npmjs.com/package/dotenv)
- Support reading config from the nearest `package.json` file
- Support extending nested configurations from multiple local or git sources

## Usage

Install package:

```sh
# npm
npm install c12

# yarn
yarn add c12

# pnpm
pnpm install c12
```

Import:

```js
// ESM
import { loadConfig } from "c12";

// CommonJS
const { loadConfig } = require("c12");
```

Load configuration:

```js
// Get loaded config
const { config } = await loadConfig({});

// Get resolved config and extended layers
const { config, configFile, layers } = await loadConfig({});
```

## Loading priority

c12 merged config sources with [unjs/defu](https://github.com/unjs/defu) by below order:

1. Config overrides passed by options
2. Config file in CWD
3. RC file in CWD
4. Global RC file in user's home directory
5. Config from `package.json`
6. Default config passed by options
7. Extended config layers

## Options

### `cwd`

Resolve configuration from this working directory. The default is `process.cwd()`

### `name`

Configuration base name. The default is `config`.

### `configName`

Configuration file name without extension. Default is generated from `name` (name=foo => `foo.config`).

Set to `false` to avoid loading the config file.

### `rcFile`

RC Config file name. Default is generated from `name` (name=foo => `.foorc`).

Set to `false` to disable loading RC config.

### `globalRC`

Load RC config from the workspace directory and the user's home directory. Only enabled when `rcFile` is provided. Set to `false` to disable this functionality.

### `dotenv`

Loads `.env` file if enabled. It is disabled by default.

### `packageJson`

Loads config from nearest `package.json` file. It is disabled by default.

If `true` value is passed, c12 uses `name` field from `package.json`.

You can also pass either a string or an array of strings as a value to use those fields.

### `defaults`

Specify default configuration. It has the **lowest** priority and is applied **after extending** config.

### `defaultConfig`

Specify default configuration. It is applied **before** extending config.

### `overrides`

Specify override configuration. It has the **highest** priority and is applied **before extending** config.

### `jiti`

Custom [unjs/jiti](https://github.com/unjs/jiti) instance used to import configuration files.

### `jitiOptions`

Custom [unjs/jiti](https://github.com/unjs/jiti) options to import configuration files.

### `envName`

Environment name used for [environment specific configuration](#environment-specific-configuration).

The default is `process.env.NODE_ENV`. You can set `envName` to `false` or an empty string to disable the feature.

## Extending configuration

If resolved config contains a `extends` key, it will be used to extend the configuration.

Extending can be nested and each layer can extend from one base or more.

The final config is merged result of extended options and user options with [unjs/defu](https://github.com/unjs/defu).

Each item in extends is a string that can be either an absolute or relative path to the current config file pointing to a config file for extending or the directory containing the config file.
If it starts with either `github:`, `gitlab:`, `bitbucket:`, or `https:`, c12 automatically clones it.

For custom merging strategies, you can directly access each layer with `layers` property.

**Example:**

```js
// config.ts
export default {
  colors: {
    primary: "user_primary",
  },
  extends: ["./theme"],
};
```

```js
// config.dev.ts
export default {
  dev: true,
};
```

```js
// theme/config.ts
export default {
  extends: "../base",
  colors: {
    primary: "theme_primary",
    secondary: "theme_secondary",
  },
};
```

```js
// base/config.ts
export default {
  colors: {
    primary: 'base_primary'
    text: 'base_text'
  }
}
```

The loaded configuration would look like this:

```js
{
  dev: true,
  colors: {
    primary: 'user_primary',
    secondary: 'theme_secondary',
    text: 'base_text'
  }
}
```

Layers:

```js
[
 { config: /* theme config */, configFile: /* path/to/theme/config.ts */, cwd: /* path/to/theme */ },
 { config: /* base  config */, configFile: /* path/to/base/config.ts  */, cwd: /* path/to/base */ },
 { config: /* dev   config */, configFile: /* path/to/config.dev.ts  */, cwd: /* path/ */ },
]
```

## Environment-specific configuration

Users can define environment-specific configuration using these config keys:

- `$test: {...}`
- `$development: {...}`
- `$production: {...}`
- `$env: { [env]: {...} }`

c12 tries to match [`envName`](#envname) and override environment config if specified.

**Note:** Environment will be applied when extending each configuration layer. This way layers can provide environment-specific configuration.

**Example:**

```js
{
  // Default configuration
  logLevel: 'info',

  // Environment overrides
  $test: { logLevel: 'silent' },
  $development: { logLevel: 'warning' },
  $production: { logLevel: 'error' },
  $env: {
    staging: { logLevel: 'debug' }
  }
}
```

## 💻 Development

- Clone this repository
- Enable [Corepack](https://github.com/nodejs/corepack) using `corepack enable` (use `npm i -g corepack` for Node.js < 16.10)
- Install dependencies using `pnpm install`
- Run interactive tests using `pnpm dev`

## License

Made with 💛 Published under [MIT License](./LICENSE).

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