webpack-chain

Use a chaining API to generate and simplify the modification of webpack version 2-4 configurations.

This documentation corresponds to v5 of webpack-chain. For previous versions, see:

• v4 docs
• v3 docs
• v2 docs
• v1 docs

Note: while webpack-chain is utilized extensively in Neutrino, this package is completely standalone and can be used by any project.

Chinese docs(中文文档)

Introduction

webpack's core configuration is based on creating and modifying a potentially unwieldy JavaScript object. While this is OK for configurations on individual projects, trying to share these objects across projects and make subsequent modifications gets messy, as you need to have a deep understanding of the underlying object structure to make those changes.

webpack-chain attempts to improve this process by providing a chainable or fluent API for creating and modifying webpack configurations. Key portions of the API can be referenced by user-specified names, which helps to standardize how to modify a configuration across projects.

This is easier explained through the examples following.

Installation

webpack-chain requires Node.js v6.9 and higher. webpack-chain also only creates configuration objects designed for use in webpack versions 2, 3, and 4.

You may install this package using either Yarn or npm (choose one):

Yarn

yarn add --dev webpack-chain

npm

npm install --save-dev webpack-chain

Getting Started

Once you have webpack-chain installed, you can start creating a webpack configuration. For this guide, our example base configuration will be webpack.config.js in the root of our project directory.

// Require the webpack-chain module. This module exports a single
// constructor function for creating a configuration API.
const Config = require('webpack-chain');

// Instantiate the configuration with a new API
const config = new Config();

// Make configuration changes using the chain API.
// Every API call tracks a change to the stored configuration.

config
  // Interact with entry points
  .entry('index')
    .add('src/index.js')
    .end()
  // Modify output settings
  .output
    .path('dist')
    .filename('[name].bundle.js');

// Create named rules which can be modified later
config.module
  .rule('lint')
    .test(/\.js$/)
    .pre()
    .include
      .add('src')
      .end()
    // Even create named uses (loaders)
    .use('eslint')
      .loader('eslint-loader')
      .options({
        rules: {
          semi: 'off'
        }
      });

config.module
  .rule('compile')
    .test(/\.js$/)
    .include
      .add('src')
      .add('test')
      .end()
    .use('babel')
      .loader('babel-loader')
      .options({
        presets: [
          ['@babel/preset-env', { modules: false }]
        ]
      });

// Create named plugins too!
config
  .plugin('clean')
    .use(CleanPlugin, [['dist'], { root: '/dir' }]);

// Export the completed configuration object to be consumed by webpack
module.exports = config.toConfig();

Having shared configurations is also simple. Just export the configuration and call .toConfig() prior to passing to webpack.

// webpack.core.js
const Config = require('webpack-chain');
const config = new Config();

// Make configuration shared across targets
// ...

module.exports = config;

// webpack.dev.js
const config = require('./webpack.core');

// Dev-specific configuration
// ...
module.exports = config.toConfig();

// webpack.prod.js
const config = require('./webpack.core');

// Production-specific configuration
// ...
module.exports = config.toConfig();

ChainedMap

One of the core API interfaces in webpack-chain is a ChainedMap. A ChainedMap operates similar to a JavaScript Map, with some conveniences for chaining and generating configuration. If a property is marked as being a ChainedMap, it will have an API and methods as described below:

Unless stated otherwise, these methods will return the ChainedMap, allowing you to chain these methods.

// Remove all entries from a Map.
clear()

// Remove a single entry from a Map given its key.
// key: *
delete(key)

// Fetch the value from a Map located at the corresponding key.
// key: *
// returns: value
get(key)

// Fetch the value from a Map located at the corresponding key.
// If the key is missing, the key is set to the result of function fn.
// key: *
// fn: Function () -> value
// returns: value
getOrCompute(key, fn)

// Set a value on the Map stored at the `key` location.
// key: *
// value: *
set(key, value)

// Returns `true` or `false` based on whether a Map as has a value set at a
// particular key.
// key: *
// returns: Boolean
has(key)

// Returns an array of all the values stored in the Map.
// returns: Array
values()

// Returns an object of all the entries in the backing Map
// where the key is the object property, and the value
// corresponding to the key. Will return `undefined` if the backing
// Map is empty.
// This will order properties by their name if the value is
// a ChainedMap that used .before() or .after().
// returns: Object, undefined if empty
entries()

// Provide an object which maps its properties and values
// into the backing Map as keys and values.
// You can also provide an array as the second argument
// for property names to omit from being merged.
// obj: Object
// omit: Optional Array
merge(obj, omit)

// Execute a function against the current configuration context
// handler: Function -> ChainedMap
  // A function which is given a single argument of the ChainedMap instance
batch(handler)

// Conditionally execute a function to continue configuration
// condition: Boolean
// whenTruthy: Function -> ChainedMap
  // invoked when condition is truthy, given a single argument of the ChainedMap instance
// whenFalsy: Optional Function -> ChainedMap
  // invoked when condition is falsy, given a single argument of the ChainedMap instance
when(condition, whenTruthy, whenFalsy)

ChainedSet

Another of the core API interfaces in webpack-chain is a ChainedSet. A ChainedSet operates similar to a JavaScript Set, with some conveniences for chaining and generating configuration. If a property is marked as being a ChainedSet, it will have an API and methods as described below:

Unless stated otherwise, these methods will return the ChainedSet, allowing you to chain these methods.

// Add/append a value to the end of a Set.
// value: *
add(value)

// Add a value to the beginning of a Set.
// value: *
prepend(value)

// Remove all values from a Set.
clear()

// Remove a specific value from a Set.
// value: *
delete(value)

// Returns `true` or `false` based on whether or not the
// backing Set contains the specified value.
// value: *
// returns: Boolean
has(value)

// Returns an array of values contained in the backing Set.
// returns: Array
values()

// Concatenates the given array to the end of the backing Set.
// arr: Array
merge(arr)

// Execute a function against the current configuration context
// handler: Function -> ChainedSet
  // A function which is given a single argument of the ChainedSet instance
batch(handler)

// Conditionally execute a function to continue configuration
// condition: Boolean
// whenTruthy: Function -> ChainedSet
  // invoked when condition is truthy, given a single argument of the ChainedSet instance
// whenFalsy: Optional Function -> ChainedSet
  // invoked when condition is falsy, given a single argument of the ChainedSet instance
when(condition, whenTruthy, whenFalsy)

Shorthand methods

A number of shorthand methods exist for setting a value on a ChainedMap with the same key as the shorthand method name. For example, devServer.hot is a shorthand method, so it can be used as:

// A shorthand method for setting a value on a ChainedMap
devServer.hot(true);

// This would be equivalent to:
devServer.set('hot', true);

A shorthand method is chainable, so calling it will return the original instance, allowing you to continue to chain.

Config

Create a new configuration object.

const Config = require('webpack-chain');

const config = new Config();

Moving to deeper points in the API will change the context of what you are modifying. You can move back to the higher context by either referencing the top-level config again, or by calling .end() to move up one level. If you are familiar with jQuery, .end() works similarly. All API calls will return the API instance at the current context unless otherwise specified. This is so you may chain API calls continuously if desired.

For details on the specific values that are valid for all shorthand and low-level methods, please refer to their corresponding name in the webpack docs hierarchy.

Config : ChainedMap

Config shorthand methods

config
  .amd(amd)
  .bail(bail)
  .cache(cache)
  .devtool(devtool)
  .context(context)
  .externals(externals)
  .loader(loader)
  .name(name)
  .mode(mode)
  .parallelism(parallelism)
  .profile(profile)
  .recordsPath(recordsPath)
  .recordsInputPath(recordsInputPath)
  .recordsOutputPath(recordsOutputPath)
  .stats(stats)
  .target(target)
  .watch(watch)
  .watchOptions(watchOptions)

Config entryPoints

// Backed at config.entryPoints : ChainedMap
config.entry(name) : ChainedSet

config
  .entry(name)
    .add(value)
    .add(value)

config
  .entry(name)
    .clear()

// Using low-level config.entryPoints:

config.entryPoints
  .get(name)
    .add(value)
    .add(value)

config.entryPoints
  .get(name)
    .clear()

Config output: shorthand methods

config.output : ChainedMap

config.output
  .auxiliaryComment(auxiliaryComment)
  .chunkFilename(chunkFilename)
  .chunkLoadTimeout(chunkLoadTimeout)
  .crossOriginLoading(crossOriginLoading)
  .devtoolFallbackModuleFilenameTemplate(devtoolFallbackModuleFilenameTemplate)
  .devtoolLineToLine(devtoolLineToLine)
  .devtoolModuleFilenameTemplate(devtoolModuleFilenameTemplate)
  .filename(filename)
  .hashFunction(hashFunction)
  .hashDigest(hashDigest)
  .hashDigestLength(hashDigestLength)
  .hashSalt(hashSalt)
  .hotUpdateChunkFilename(hotUpdateChunkFilename)
  .hotUpdateFunction(hotUpdateFunction)
  .hotUpdateMainFilename(hotUpdateMainFilename)
  .jsonpFunction(jsonpFunction)
  .library(library)
  .libraryExport(libraryExport)
  .libraryTarget(libraryTarget)
  .path(path)
  .pathinfo(pathinfo)
  .publicPath(publicPath)
  .sourceMapFilename(sourceMapFilename)
  .sourcePrefix(sourcePrefix)
  .strictModuleExceptionHandling(strictModuleExceptionHandling)
  .umdNamedDefine(umdNamedDefine)

Config resolve: shorthand methods

config.resolve : ChainedMap

config.resolve
  .cachePredicate(cachePredicate)
  .cacheWithContext(cacheWithContext)
  .enforceExtension(enforceExtension)
  .enforceModuleExtension(enforceModuleExtension)
  .unsafeCache(unsafeCache)
  .symlinks(symlinks)

Config resolve alias

config.resolve.alias : ChainedMap

config.resolve.alias
  .set(key, value)
  .set(key, value)
  .delete(key)
  .clear()

Config resolve modules

config.resolve.modules : ChainedSet

config.resolve.modules
  .add(value)
  .prepend(value)
  .clear()

Config resolve aliasFields

config.resolve.aliasFields : ChainedSet

config.resolve.aliasFields
  .add(value)
  .prepend(value)
  .clear()

Config resolve descriptionFields

config.resolve.descriptionFields : ChainedSet

config.resolve.descriptionFields
  .add(value)
  .prepend(value)
  .clear()

Config resolve extensions

config.resolve.extensions : ChainedSet

config.resolve.extensions
  .add(value)
  .prepend(value)
  .clear()

Config resolve mainFields

config.resolve.mainFields : ChainedSet

config.resolve.mainFields
  .add(value)
  .prepend(value)
  .clear()

Config resolve mainFiles

config.resolve.mainFiles : ChainedSet

config.resolve.mainFiles
  .add(value)
  .prepend(value)
  .clear()

Config resolveLoader

The API for config.resolveLoader is identical to config.resolve with the following additions:

Config resolveLoader moduleExtensions

config.resolveLoader.moduleExtensions : ChainedSet

config.resolveLoader.moduleExtensions
  .add(value)
  .prepend(value)
  .clear()

Config resolveLoader packageMains

config.resolveLoader.packageMains : ChainedSet

config.resolveLoader.packageMains
  .add(value)
  .prepend(value)
  .clear()

Config performance: shorthand methods

config.performance : ChainedMap

config.performance
  .hints(hints)
  .maxEntrypointSize(maxEntrypointSize)
  .maxAssetSize(maxAssetSize)
  .assetFilter(assetFilter)

Configuring optimizations: shorthand methods

config.optimization : ChainedMap

config.optimization
  .concatenateModules(concatenateModules)
  .flagIncludedChunks(flagIncludedChunks)
  .mergeDuplicateChunks(mergeDuplicateChunks)
  .minimize(minimize)
  .namedChunks(namedChunks)
  .namedModules(namedModules)
  .nodeEnv(nodeEnv)
  .noEmitOnErrors(noEmitOnErrors)
  .occurrenceOrder(occurrenceOrder)
  .portableRecords(portableRecords)
  .providedExports(providedExports)
  .removeAvailableModules(removeAvailableModules)
  .removeEmptyChunks(removeEmptyChunks)
  .runtimeChunk(runtimeChunk)
  .sideEffects(sideEffects)
  .splitChunks(splitChunks)
  .usedExports(usedExports)

Config optimization minimizers

// Backed at config.optimization.minimizers
config.optimization
  .minimizer(name) : ChainedMap

Config optimization minimizers: adding

NOTE: Do not use new to create the minimizer plugin, as this will be done for you.

config.optimization
  .minimizer(name)
  .use(WebpackPlugin, args)

// Examples

config.optimization
  .minimizer('css')
  .use(OptimizeCSSAssetsPlugin, [{ cssProcessorOptions: { safe: true } }])

// Minimizer plugins can also be specified by their path, allowing the expensive require()s to be
// skipped in cases where the plugin or webpack configuration won't end up being used.
config.optimization
  .minimizer('css')
  .use(require.resolve('optimize-css-assets-webpack-plugin'), [{ cssProcessorOptions: { safe: true } }])

Config optimization minimizers: modify arguments

config.optimization
  .minimizer(name)
  .tap(args => newArgs)

// Example
config.optimization
  .minimizer('css')
  .tap(args => [...args, { cssProcessorOptions: { safe: false } }])

Config optimization minimizers: modify instantiation

config.optimization
  .minimizer(name)
  .init((Plugin, args) => new Plugin(...args));

Config optimization minimizers: removing

config.optimization.minimizers.delete(name)

Config plugins

// Backed at config.plugins
config.plugin(name) : ChainedMap

Config plugins: adding

NOTE: Do not use new to create the plugin, as this will be done for you.

config
  .plugin(name)
  .use(WebpackPlugin, args)

// Examples

config
  .plugin('hot')
  .use(webpack.HotModuleReplacementPlugin);

// Plugins can also be specified by their path, allowing the expensive require()s to be
// skipped in cases where the plugin or webpack configuration won't end up being used.
config
  .plugin('env')
  .use(require.resolve('webpack/lib/EnvironmentPlugin'), [{ 'VAR': false }]);

Config plugins: modify arguments

config
  .plugin(name)
  .tap(args => newArgs)

// Example
config
  .plugin('env')
  .tap(args => [...args, 'SECRET_KEY']);

Config plugins: modify instantiation

config
  .plugin(name)
  .init((Plugin, args) => new Plugin(...args));

Config plugins: removing

config.plugins.delete(name)

Config plugins: ordering before

Specify that the current plugin context should operate before another named plugin. You cannot use both .before() and .after() on the same plugin.

config
  .plugin(name)
    .before(otherName)

// Example

config
  .plugin('html-template')
    .use(HtmlWebpackTemplate)
    .end()
  .plugin('script-ext')
    .use(ScriptExtWebpackPlugin)
    .before('html-template');

Config plugins: ordering after

Specify that the current plugin context should operate after another named plugin. You cannot use both .before() and .after() on the same plugin.

config
  .plugin(name)
    .after(otherName)

// Example

config
  .plugin('html-template')
    .after('script-ext')
    .use(HtmlWebpackTemplate)
    .end()
  .plugin('script-ext')
    .use(ScriptExtWebpackPlugin);

Config resolve plugins

// Backed at config.resolve.plugins
config.resolve.plugin(name) : ChainedMap

Config resolve plugins: adding

NOTE: Do not use new to create the plugin, as this will be done for you.

config.resolve
  .plugin(name)
  .use(WebpackPlugin, args)

Config resolve plugins: modify arguments

config.resolve
  .plugin(name)
  .tap(args => newArgs)

Config resolve plugins: modify instantiation

config.resolve
  .plugin(name)
  .init((Plugin, args) => new Plugin(...args))

Config resolve plugins: removing

config.resolve.plugins.delete(name)

Config resolve plugins: ordering before

Specify that the current plugin context should operate before another named plugin. You cannot use both .before() and .after() on the same resolve plugin.

config.resolve
  .plugin(name)
    .before(otherName)

// Example

config.resolve
  .plugin('beta')
    .use(BetaWebpackPlugin)
    .end()
  .plugin('alpha')
    .use(AlphaWebpackPlugin)
    .before('beta');

Config resolve plugins: ordering after

Specify that the current plugin context should operate after another named plugin. You cannot use both .before() and .after() on the same resolve plugin.

config.resolve
  .plugin(name)
    .after(otherName)

// Example

config.resolve
  .plugin('beta')
    .after('alpha')
    .use(BetaWebpackTemplate)
    .end()
  .plugin('alpha')
    .use(AlphaWebpackPlugin);

Config node

config.node : ChainedMap

config.node
  .set('__dirname', 'mock')
  .set('__filename', 'mock');

Config devServer

config.devServer : ChainedMap

Config devServer allowedHosts

config.devServer.allowedHosts : ChainedSet

config.devServer.allowedHosts
  .add(value)
  .prepend(value)
  .clear()

Config devServer: shorthand methods

config.devServer
  .bonjour(bonjour)
  .clientLogLevel(clientLogLevel)
  .color(color)
  .compress(compress)
  .contentBase(contentBase)
  .disableHostCheck(disableHostCheck)
  .filename(filename)
  .headers(headers)
  .historyApiFallback(historyApiFallback)
  .host(host)
  .hot(hot)
  .hotOnly(hotOnly)
  .https(https)
  .inline(inline)
  .info(info)
  .lazy(lazy)
  .noInfo(noInfo)
  .open(open)
  .openPage(openPage)
  .overlay(overlay)
  .pfx(pfx)
  .pfxPassphrase(pfxPassphrase)
  .port(port)
  .progress(progress)
  .proxy(proxy)
  .public(public)
  .publicPath(publicPath)
  .quiet(quiet)
  .setup(setup)
  .socket(socket)
  .staticOptions(staticOptions)
  .stats(stats)
  .stdin(stdin)
  .useLocalIp(useLocalIp)
  .watchContentBase(watchContentBase)
  .watchOptions(watchOptions)

Config module

config.module : ChainedMap

Config module: shorthand methods

config.module : ChainedMap

config.module
  .noParse(noParse)

Config module rules: shorthand methods

config.module.rules : ChainedMap

config.module
  .rule(name)
    .test(test)
    .pre()
    .post()
    .enforce(preOrPost)

Config module rules uses (loaders): creating

config.module.rules{}.uses : ChainedMap

config.module
  .rule(name)
    .use(name)
      .loader(loader)
      .options(options)

// Example

config.module
  .rule('compile')
    .use('babel')
      .loader('babel-loader')
      .options({ presets: ['@babel/preset-env'] });

Config module rules uses (loaders): modifying options

config.module
  .rule(name)
    .use(name)
      .tap(options => newOptions)

// Example

config.module
  .rule('compile')
    .use('babel')
      .tap(options => merge(options, {
        plugins: ['@babel/plugin-proposal-class-properties']
      }));

Config module rules oneOfs (conditional rules):

config.module.rules{}.oneOfs : ChainedMap<Rule>

config.module
  .rule(name)
    .oneOf(name)

// Example

config.module
  .rule('css')
    .oneOf('inline')
      .resourceQuery(/inline/)
      .use('url')
        .loader('url-loader')
        .end()
      .end()
    .oneOf('external')
      .resourceQuery(/external/)
      .use('file')
        .loader('file-loader')

Config module rules oneOfs (conditional rules): ordering before

Specify that the current oneOf context should operate before another named oneOf. You cannot use both .before() and .after() on the same oneOf.

config.module
  .rule(name)
    .oneOf(name)
      .before()

// Example

config.module
  .rule('scss')
    .test(/\.scss$/)
    .oneOf('normal')
      .use('sass')
        .loader('sass-loader')
        .end()
      .end()
    .oneOf('sass-vars')
      .before('normal')
      .resourceQuery(/\?sassvars/)
      .use('sass-vars')
        .loader('sass-vars-to-js-loader')

Config module rules oneOfs (conditional rules): ordering after

Specify that the current oneOf context should operate after another named oneOf. You cannot use both .before() and .after() on the same oneOf.

config.module
  .rule(name)
    .oneOf(name)
      .after()

// Example

config.module
  .rule('scss')
    .test(/\.scss$/)
    .oneOf('vue')
      .resourceQuery(/\?vue/)
      .use('vue-style')
        .loader('vue-style-loader')
        .end()
      .end()
    .oneOf('normal')
      .use('sass')
        .loader('sass-loader')
        .end()
      .end()
    .oneOf('sass-vars')
      .after('vue')
      .resourceQuery(/\?sassvars/)
      .use('sass-vars')
        .loader('sass-vars-to-js-loader')

---

Merging Config

webpack-chain supports merging in an object to the configuration instance which matches a layout similar to how the webpack-chain schema is laid out. Note that this is not a webpack configuration object, but you may transform a webpack configuration object before providing it to webpack-chain to match its layout.

config.merge({ devtool: 'source-map' });

config.get('devtool') // "source-map"

config.merge({
  [key]: value,

  amd,
  bail,
  cache,
  context,
  devtool,
  externals,
  loader,
  mode,
  parallelism,
  profile,
  recordsPath,
  recordsInputPath,
  recordsOutputPath,
  stats,
  target,
  watch,
  watchOptions,

  entry: {
    [name]: [...values]
  },

  plugin: {
    [name]: {
      plugin: WebpackPlugin,
      args: [...args],
      before,
      after
    }
  },

  devServer: {
    [key]: value,

    clientLogLevel,
    compress,
    contentBase,
    filename,
    headers,
    historyApiFallback,
    host,
    hot,
    hotOnly,
    https,
    inline,
    lazy,
    noInfo,
    overlay,
    port,
    proxy,
    quiet,
    setup,
    stats,
    watchContentBase
  },

  node: {
    [key]: value
  },

  optimization: {
    concatenateModules,
    flagIncludedChunks,
    mergeDuplicateChunks,
    minimize,
    minimizer,
    namedChunks,
    namedModules,
    nodeEnv,
    noEmitOnErrors,
    occurrenceOrder,
    portableRecords,
    providedExports,
    removeAvailableModules,
    removeEmptyChunks,
    runtimeChunk,
    sideEffects,
    splitChunks,
    usedExports,
  },

  performance: {
    [key]: value,

    hints,
    maxEntrypointSize,
    maxAssetSize,
    assetFilter
  },

  resolve: {
    [key]: value,

    alias: {
      [key]: value
    },
    aliasFields: [...values],
    descriptionFields: [...values],
    extensions: [...values],
    mainFields: [...values],
    mainFiles: [...values],
    modules: [...values],

    plugin: {
      [name]: {
        plugin: WebpackPlugin,
        args: [...args],
        before,
        after
      }
    }
  },

  resolveLoader: {
    [key]: value,

    alias: {
      [key]: value
    },
    aliasFields: [...values],
    descriptionFields: [...values],
    extensions: [...values],
    mainFields: [...values],
    mainFiles: [...values],
    modules: [...values],
    moduleExtensions: [...values],
    packageMains: [...values],

    plugin: {
      [name]: {
        plugin: WebpackPlugin,
        args: [...args],
        before,
        after
      }
    }
  },

  module: {
    [key]: value,

    rule: {
      [name]: {
        [key]: value,

        enforce,
        issuer,
        parser,
        resource,
        resourceQuery,
        test,

        include: [...paths],
        exclude: [...paths],

        oneOf: {
          [name]: Rule
        },

        use: {
          [name]: {
            loader: LoaderString,
            options: LoaderOptions,
            before,
            after
          }
        }
      }
    }
  }
})

Conditional configuration

When working with instances of ChainedMap and ChainedSet, you can perform conditional configuration using when. You must specify an expression to when() which will be evaluated for truthiness or falsiness. If the expression is truthy, the first function argument will be invoked with an instance of the current chained instance. You can optionally provide a second function to be invoked when the condition is falsy, which is also given the current chained instance.

// Example: Only add minify plugin during production
config
  .when(process.env.NODE_ENV === 'production', config => {
    config
      .plugin('minify')
      .use(BabiliWebpackPlugin);
  });

// Example: Only add minify plugin during production,
// otherwise set devtool to source-map
config
  .when(process.env.NODE_ENV === 'production',
    config => config.plugin('minify').use(BabiliWebpackPlugin),
    config => config.devtool('source-map')
  );

Inspecting generated configuration

You can inspect the generated webpack config using config.toString(). This will generate a stringified version of the config with comment hints for named rules, uses and plugins:

config
  .module
    .rule('compile')
      .test(/\.js$/)
      .use('babel')
        .loader('babel-loader');

config.toString();

/*
{
  module: {
    rules: [
      /* config.module.rule('compile') */
      {
        test: /\.js$/,
        use: [
          /* config.module.rule('compile').use('babel') */
          {
            loader: 'babel-loader'
          }
        ]
      }
    ]
  }
}
*/

By default the generated string cannot be used directly as real webpack config if it contains objects and plugins that need to be required. In order to generate usable config, you can customize how objects and plugins are stringified by setting a special __expression property on them:

const sass = require('sass');
sass.__expression = `require('sass');

class MyPlugin {}
MyPlugin.__expression = `require('my-plugin')`;

function myFunction () {}
myFunction.__expression = `require('my-function')`;

config
  .plugin('example')
    .use(MyPlugin, [{ fn: myFunction, implementation: sass, }]);

config.toString();

/*
{
  plugins: [
    new (require('my-plugin'))({
      fn: require('my-function'),
      implementation: require('sass')
    })
  ]
}
*/

Plugins specified via their path will have their require() statement generated automatically:

config
  .plugin('env')
    .use(require.resolve('webpack/lib/ProvidePlugin'), [{ jQuery: 'jquery' }])

config.toString();

/*
{
  plugins: [
    new (require('/foo/bar/src/node_modules/webpack/lib/EnvironmentPlugin.js'))(
      {
        jQuery: 'jquery'
      }
    )
  ]
}
*/

You can also call toString as a static method on Config in order to modify the configuration object prior to stringifying.

Config.toString({
  ...config.toConfig(),
  module: {
    defaultRules: [
      {
        use: [
          {
            loader: 'banner-loader',
            options: { prefix: 'banner-prefix.txt' },
          },
        ],
      },
    ],
  },
})

{
  plugins: [
    /* config.plugin('foo') */
    new TestPlugin()
  ],
  module: {
    defaultRules: [
      {
        use: [
          {
            loader: 'banner-loader',
            options: {
              prefix: 'banner-prefix.txt'
            }
          }
        ]
      }
    ]
  }
}