ex-config is an extendable configuration processor. It is used to merge multiple configurations together like babel and eslint configurations do.
npm install --save ex-config
'use strict';
const cosmiconfig = require('cosmiconfig');
const {
/* async: */ exConfig,
/* sync: */ exConfigSync,
} = require('ex-config');
/**
* Example using cosmiconfig to load the base config from disk
*/
const explorer = cosmiconfig('example');
const baseConfig = await explorer.load();
/**
* Original configs are not mutated
*
* all options are optional
*
* preprocessor, validator, processor, and postProcessor lifecycles all
* are given one argument object containing:
* {
* value: new value
* current: current value, can be undefined
* config: current config
* dirname: directory where the preset was loaded from
* }
*/
const config = await exConfig(
/* initial config: */ baseConfig,
/* options: */ {
/**
* directory to initially resolve presets/plugins from
*
* default: process.cwd()
*/
baseDirectory: process.cwd(),
/**
* Add an API accessible to all lifecycles/presets/plugins
*
* default: {}
*/
api: new (class ApiExample {
someCustomApiExample() {
return this;
}
})(),
/**
* key id that extends configurations via resolve
* See also, overrides.presets.resolve
*
* default: 'presets'
* set to false to disable
*/
presets: 'presets',
/**
* key id that resolves plugins
*
* default: 'plugins'
* set to false to disable
*/
plugins: 'plugins',
/**
* Pre-process the preset before validation
*
* Whatever is returned will be the new value of the current preset
*
* Runs once with each preset
*/
preprocessor: async ({ value, current, config, dirname, api }) => {
// returned value will be the updated preset value
return value;
},
/**
* Used to validate a preset. if preset is invalid, throw with an error
*
* Runs once with each preset
*/
validator: async ({ value, current, config, dirname, api }) => {
if (value !== 'valid') {
throw new Error('value is invalid');
}
// does not expect a return value
return undefined;
},
/**
* Post Processor runs once after all configurations
* have been successfully processed.
*/
postProcessor: async ({ config, dirname, api }) => {
// returned value will equal the final config
return value;
},
/**
* processor runs once per key per preset
*
* used merge the value with the overall current value
*
* by default, this will deep merge any objects,
* push new value onto array, or replace current value
*
* other built-in processors are:
* arrayPush: all values are an array that are appended
* to the end of the current array
*
* arrayConcat: all values are an array that are added
* to the front of the current array
*
* mergeDeep: all values are treated as an object
*
* Pass a function to use a custom processor
*/
processor: async ({ value, current = [], config, dirname, api }) => {
const val = Array.isArray(value) ? value : [value];
// returned value will be the new value of the key
return [
...current,
...val,
];
},
/**
* overrides can override/change the settings above
*/
overrides: {
presets: {
resolve: {
/**
* Prefix to add to packageId
*
* example: one -> example-preset-one
*
* Optional
*
* Accepts a single or an array of prefixes
*/
prefix: 'example-preset',
/**
* NPM Scope of organization to override prefix
*
* Optional
*/
org: '@example',
/**
* Org prefixes
*
* example: @example/one -> @example/preset-one
*
* Optional
*
* Accepts a single or an array of prefixes
*/
orgPrefix: 'preset',
/**
* Only allow prefixed module resolution.
* Explicit modules can be required by prepending module:
* For example, module:local-module
*
* Default: true
* Optional
*/
strict: true,
},
},
files: {
/**
* preprocessor override is in addition to the base preprocessor
*/
preprocessor: async ({
value,
current,
config,
dirname,
api,
}) => {
return value;
},
/**
* validator override will validate in addition to the base validator
*/
validator: async ({ value, current, config, dirname, api }) => {
if (typeof value.source !== 'string') {
throw new Error('files source must be a string');
}
},
/**
* processor override will override the base processor
*/
processor: async ({
value,
current = [],
config,
dirname,
api,
}) => {
const val = Array.isArray(value) ? value : [value];
return [
...val,
...current,
];
},
},
},
},
);A preset or plugin needs to export an object or function.
Only export default is supported when using es modules.
If a function is used it will be invoked with the following argument:
// preset-example.js
function presetExample(context) {
// options given as second index when calling preset/plugin
const options = context.options;
// dirname package was found from
const dirname = context.dirname;
// api provided in options
const api = context.api;
return {
verbose: options.verbose,
};
}
module.exports = presetExample;
// config.js
const exampleConfig = {
presets: [
[
// packageId
'preset-example',
// options for preset/plugin
{ verbose: true },
],
],
};
module.exports = exampleConfig;This package was created with the great work / lessons learned from: