⚙️ c12

Smart Configuration Loader.

Features

• JSON, CJS, Typescript, and ESM config loader with unjs/jiti
• RC config support with unjs/rc9
• Multiple sources merged with unjs/defu
• .env support with dotenv
• Reads config from the nearest package.json file
• Extends configurations from multiple local or git sources
• Overwrite with environment-specific configuration
• Config watcher with auto-reload and HMR support

Usage

Install package:

# npm
npm install c12

# yarn
yarn add c12

# pnpm
pnpm install c12

Import:

// ESM
import { loadConfig, watchConfig } from "c12";

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

Load configuration:

// 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 by below order:

1. Config overrides passed by options
2. Config file in CWD
3. RC file in CWD
4. Global RC file in the 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.

configFile

Configuration file name without extension. Default is generated from name (f.e., if name is foo, the config file will be => 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 instance used to import configuration files.

jitiOptions

Custom unjs/jiti options to import configuration files.

envName

Environment name used for 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.

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:

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

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

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

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

The loaded configuration would look like this:

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

Layers:

[
 { 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 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:

{
  // Default configuration
  logLevel: 'info',

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

Watching Configuration

you can use watchConfig instead of loadConfig to load config and watch for changes, add and removals in all expected configuration paths and auto reload with new config.

Lifecycle hooks

• onWatch: This function is always called when config is updated, added, or removed before attempting to reload the config.
• acceptHMR: By implementing this function, you can compare old and new functions and return true if a full reload is not needed.
• onUpdate: This function is always called after the new config is updated. If acceptHMR returns true, it will be skipped.

import { watchConfig } from "c12";

const config = watchConfig({
  cwd: ".",
  // chokidarOptions: {}, // Default is { ignoreInitial: true }
  // debounce: 200 // Default is 100. You can set it to false to disable debounced watcher
  onWatch: (event) => {
    console.log("[watcher]", event.type, event.path);
  },
  acceptHMR({ oldConfig, newConfig, getDiff }) {
    const diff = getDiff();
    if (diff.length === 0) {
      console.log("No config changed detected!");
      return true; // No changes!
    }
  },
  onUpdate({ oldConfig, newConfig, getDiff }) {
    const diff = getDiff();
    console.log("Config updated:\n" + diff.map((i) => i.toJSON()).join("\n"));
  },
});

console.log("watching config files:", config.watchingFiles);
console.log("initial config", config.config);

// Stop watcher when not needed anymore
// await config.unwatch();

💻 Development

• Clone this repository
• Enable 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.