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minimizer-webpack-plugin

This plugin minifies your assets in a webpack build. It ships with several built-in minimizers covering JavaScript, JSON, HTML, CSS, and images — pick one with the minify option and target the right files with test.

JavaScript minimizers:

  • terser — MinimizerPlugin.terserMinify (default). The same JavaScript-based minifier that webpack uses out of the box; produces small, well-tested output and supports the full set of extractComments modes.
  • uglify-js — MinimizerPlugin.uglifyJsMinify. ES5-only minifier, useful when you specifically need UglifyJS-compatible output. Requires npm install --save-dev uglify-js.
  • @swc/core — MinimizerPlugin.swcMinify. A very fast Rust-based JavaScript/TypeScript minifier. Requires npm install --save-dev @swc/core.
  • esbuild — MinimizerPlugin.esbuildMinify. An extremely fast JS bundler/minifier; legal comments are always preserved (no extractComments support). Requires npm install --save-dev esbuild.

JSON minimizer:

  • JSON.stringify — MinimizerPlugin.jsonMinify. Built in (no extra dependency); supports space and replacer options.

HTML minimizers:

  • html-minifier-terser — MinimizerPlugin.htmlMinifierTerser. The default HTML minimizer. JavaScript-based, no native dependency. Requires npm install --save-dev html-minifier-terser.
  • @swc/html — MinimizerPlugin.swcMinifyHtml (full HTML documents) and MinimizerPlugin.swcMinifyHtmlFragment (HTML fragments, e.g. <template> content). Very fast Rust-based platform for the Web. Requires npm install --save-dev @swc/html.
  • @minify-html/node — MinimizerPlugin.minifyHtmlNode. A Rust HTML minifier optimised for speed and effectiveness. Requires npm install --save-dev @minify-html/node.

CSS minimizers:

  • cssnano — MinimizerPlugin.cssnanoMinify. The default CSS minimizer. Built on top of PostCSS. Requires npm install --save-dev cssnano postcss.
  • csso — MinimizerPlugin.cssoMinify. A CSS minifier with structural optimisations. Requires npm install --save-dev csso.
  • clean-css — MinimizerPlugin.cleanCssMinify. A widely-used CSS optimiser. Requires npm install --save-dev clean-css.
  • esbuild — MinimizerPlugin.esbuildMinifyCss. Very fast CSS minification using esbuild's CSS loader. Requires npm install --save-dev esbuild.
  • lightningcss — MinimizerPlugin.lightningCssMinify. A Rust-based CSS parser, transformer, and minifier. Requires npm install --save-dev lightningcss.
  • @swc/css — MinimizerPlugin.swcMinifyCss. A very fast Rust-based CSS minifier. Requires npm install --save-dev @swc/css.

Image minimizers:

  • sharp — MinimizerPlugin.sharpMinify. Re-encodes an image as the format its name already claims (avif, gif, heif, jp2, jpeg, png, tiff, webp), and can resize, rotate, flip, grayscale, blur or sharpen on the way — from the options or from the asset's own name. Requires npm install --save-dev sharp.
  • svgo — MinimizerPlugin.svgoMinify. Minifies SVG, including an asset/inline SVG that no test can match. Requires npm install --save-dev svgo.
  • imagemin — MinimizerPlugin.imageminMinify. Runs the imagemin plugins you name. Requires npm install --save-dev imagemin plus each plugin. Pair it with MinimizerPlugin.imageminGenerate under generate when a plugin converts the format, since only that can rename the asset.
  • @napi-rs/image — MinimizerPlugin.napiRsImageMinify. Rust codecs with no system dependency; recompresses png losslessly with oxipng and jpeg with mozjpeg, and can resize, turn, mirror, grayscale, invert or blur on the way — from the options or from the asset's own name. Requires npm install --save-dev @napi-rs/image.

These only minify — they never change an image's format or name; see Images.

All of the non-default minimizers are declared as optional peer dependencies — install only the ones you actually use. You can also stack multiple MinimizerPlugin instances in the same build to handle different file types with different minimizers (see Examples).

Getting Started

Webpack v5 comes with the latest minimizer-webpack-plugin out of the box. If you are using Webpack v5 or above and wish to customize the options, you will still need to install minimizer-webpack-plugin. Using Webpack v4, you have to install terser-webpack-plugin v4 (minimizer-webpack-plugin is only published for Webpack v5+).

To begin, you'll need to install minimizer-webpack-plugin:

npm install minimizer-webpack-plugin --save-dev

or

yarn add -D minimizer-webpack-plugin

or

pnpm add -D minimizer-webpack-plugin

Then add the plugin to your webpack configuration. For example:

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [new MinimizerPlugin()],
  },
};

Finally, run webpack using the method you normally use (e.g., via CLI or an npm script).

Note about source maps

Works only with source-map, inline-source-map, hidden-source-map and nosources-source-map values for the devtool option.

Why?

  • eval wraps modules in eval("string") and the minimizer does not handle strings.
  • cheap has no column information and the minimizer generates only a single line, which leaves only a single mapping.

Using supported devtool values enable source map generation.

Options

test

Type:

type test = string | RegExp | (string | RegExp)[];

Default: /\.m?js(\?.*)?$/i

Test to match files against.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        test: /\.js(\?.*)?$/i,
      }),
    ],
  },
};

include

Type:

type include = string | RegExp | (string | RegExp)[];

Default: undefined

Files to include.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        include: /\/includes/,
      }),
    ],
  },
};

exclude

Type:

type exclude = string | RegExp | (string | RegExp)[];

Default: undefined

Files to exclude.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        exclude: /\/excludes/,
      }),
    ],
  },
};

parallel

Type:

type parallel = boolean | number;

Default: true

Use multi-process parallel running to improve the build speed.

Default number of concurrent runs: os.cpus().length - 1 or os.availableParallelism() - 1 (if this function is supported).

Note

Parallelization can speedup your build significantly and is therefore highly recommended.

Warning

If you use Circle CI or any other environment that doesn't provide the real available count of CPUs then you need to explicitly set up the number of CPUs to avoid Error: Call retries were exceeded (see #143, #202).

boolean

Enable/disable multi-process parallel running.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        parallel: true,
      }),
    ],
  },
};

number

Enable multi-process parallel running and set number of concurrent runs.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        parallel: 4,
      }),
    ],
  },
};

minify

Type:

type minifyFn = (
  input: Record<string, string | Buffer>,
  sourceMap: import("@jridgewell/trace-mapping").SourceMapInput | undefined,
  minifyOptions: {
    module?: boolean | undefined;
    ecma?: import("terser").ECMA | undefined;
  },
  extractComments:
    | boolean
    | "all"
    | "some"
    | RegExp
    | ((
        astNode: any,
        comment: {
          value: string;
          type: "comment1" | "comment2" | "comment3" | "comment4";
          pos: number;
          line: number;
          col: number;
        },
      ) => boolean)
    | {
        condition?:
          | boolean
          | "all"
          | "some"
          | RegExp
          | ((
              astNode: any,
              comment: {
                value: string;
                type: "comment1" | "comment2" | "comment3" | "comment4";
                pos: number;
                line: number;
                col: number;
              },
            ) => boolean)
          | undefined;
        filename?: string | ((fileData: any) => string) | undefined;
        banner?:
          string | boolean | ((commentsFile: string) => string) | undefined;
      }
    | undefined,
) => Promise<{
  code: string;
  map?: import("@jridgewell/trace-mapping").SourceMapInput | undefined;
  errors?: (string | Error)[] | undefined;
  warnings?: (string | Error)[] | undefined;
  extractedComments?: string[] | undefined;
}>;

type minify = minifyFn | minifyFn[];

Default: MinimizerPlugin.terserMinify

Allows you to override the default minify function. By default plugin uses terser package. Useful for using and testing unpublished versions or forks.

An array of functions can also be provided. Each minimizer can expose a filter(name, info) helper that decides whether it should run on a given asset; the plugin dispatches each asset only to the minimizers whose filter accepts it (or runs them all when no filter is set). All built-in minimizers ship with a filter that matches their natural extension, so a single plugin instance and a single worker pool can handle JS, CSS, HTML and JSON together without juggling multiple MinimizerPlugin instances — just widen test to let those asset types reach the dispatcher:

new MinimizerPlugin({
  test: /\.(?:[cm]?js|css|html?|json)(\?.*)?$/i,
  minify: [
    MinimizerPlugin.terserMinify,
    MinimizerPlugin.cssnanoMinify,
    MinimizerPlugin.htmlMinifierTerser,
    MinimizerPlugin.jsonMinify,
  ],
});

When more than one minimizer in the array claims the same asset, the chain semantic still applies: the output of each accepting minimizer is fed as input to the next. The minimizerOptions option may be an array (index-paired with minify) or a single object reused by every minimizer.

The test option always defaults to /\.[cm]?js(\?.*)?$/i. When you mix asset types in a single plugin instance, widen test so non-JS assets reach the dispatcher (for example test: /\.(?:[cm]?js|css|html?|json)(\?.*)?$/i).

Warning

Always use require inside minify function when parallel option enabled.

function

webpack.config.js

// Can be async
const minify = (input, sourceMap, minimizerOptions, extractsComments) => {
  // The `minimizerOptions` argument contains options from the `minimizerOptions` plugin option
  // You can use `minimizerOptions.myCustomOption`

  // Custom logic for extract comments
  const { map, code } = require("uglify-module") // Or require('./path/to/uglify-module')
    .minify(input, {/* Your options for minification */});

  return { map, code, warnings: [], errors: [], extractedComments: [] };
};

// Used to regenerate `fullhash`/`chunkhash` between different implementation
// Example: you fix a bug in custom minimizer/custom function, but unfortunately webpack doesn't know about it, so you will get the same fullhash/chunkhash
// to avoid this you can provide version of your custom minimizer
// You don't need if you use only `contenthash`
minify.getMinimizerVersion = () => {
  let packageJson;

  try {
    packageJson = require("uglify-module/package.json");
  } catch (error) {
    // Ignore
  }

  return packageJson && packageJson.version;
};

// Restrict the minimizer to the assets it can actually handle. The plugin
// skips assets for which `filter` returns `false` and (when an array of
// minimizers is used) dispatches each asset only to the minimizers that
// accept it. Returning `undefined` is treated as accept.
minify.filter = (name) => /\.[cm]?js(\?.*)?$/i.test(name);

// Declare this when the minimizer reads the asset's bytes rather than its
// text — an image minimizer. Its `input` values then arrive as a `Buffer` and
// its `code` may be one. Only applied when every minimizer an asset is
// dispatched to declares it, since one that does not could not read the bytes.
minify.supportsBinary = () => true;

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minimizerOptions: {
          myCustomOption: true,
        },
        minify,
      }),
    ],
  },
};

array

If an array of functions is passed to the minify option, each asset is dispatched to the minimizers whose filter accepts it. When more than one minimizer accepts the same asset the output of each is fed as input to the next one (the chain semantic). The minimizerOptions option can be either an array of option objects (index-paired with minify) or a single object that will be shared by all minimizers. Warnings, errors and extracted comments from all running minimizers are merged together.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minify: [MinimizerPlugin.terserMinify, MinimizerPlugin.swcMinify],
        // `minimizerOptions` can be an array of options, one per `minify` entry
        minimizerOptions: [
          // Options for `MinimizerPlugin.terserMinify`
          { mangle: false },
          // Options for `MinimizerPlugin.swcMinify`
          {},
        ],
      }),
    ],
  },
};

A single plugin instance can also handle multiple asset types — the built-in minimizers each ship with a filter matching their natural extension, so JS, CSS, HTML and JSON can all be minified by one shared worker pool:

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        // `test` still defaults to JS only, so widen it to catch every
        // asset type you want the dispatcher to consider.
        test: /\.(?:[cm]?js|css|html?|json)(\?.*)?$/i,
        minify: [
          MinimizerPlugin.terserMinify,
          MinimizerPlugin.cssnanoMinify,
          MinimizerPlugin.htmlMinifierTerser,
          MinimizerPlugin.jsonMinify,
        ],
      }),
    ],
  },
};

minimizerOptions

Type:

interface minimizerOptions {
  compress?: boolean | CompressOptions;
  ecma?: ECMA;
  enclose?: boolean | string;
  ie8?: boolean;
  keep_classnames?: boolean | RegExp;
  keep_fnames?: boolean | RegExp;
  mangle?: boolean | MangleOptions;
  module?: boolean;
  nameCache?: object;
  format?: FormatOptions;
  /** @deprecated */
  output?: FormatOptions;
  parse?: ParseOptions;
  safari10?: boolean;
  sourceMap?: boolean | SourceMapOptions;
  toplevel?: boolean;
}

type options = minimizerOptions | minimizerOptions[];

Default: default

Options for the active minimizer. With the default Terser minify, see Terser's minify options.

When the minify option is an array of minimizers, minimizerOptions can also be an array. Each element is passed to the minimizer at the same index in the minify array. If a single object is provided instead, it is reused for every minimizer.

Two keys are filled in before a minimizer sees them, and only when the options do not already set them: ecma, from output.environment, and module, from the asset's own javascriptModule info or its .mjs / .cjs extension. Setting either yourself wins, including module: false.

Note

terserOptions is kept as a deprecated alias of minimizerOptions for backwards compatibility — passing either is equivalent. If both are set, minimizerOptions wins. Prefer minimizerOptions in new code.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minimizerOptions: {
          ecma: undefined,
          parse: {},
          compress: {},
          mangle: true, // Note `mangle.properties` is `false` by default.
          module: false,
          // Deprecated
          output: null,
          format: null,
          toplevel: false,
          nameCache: null,
          ie8: false,
          keep_classnames: undefined,
          keep_fnames: false,
          safari10: false,
        },
      }),
    ],
  },
};

generate

Type:

type generateFn = (
  input: Record<string, string | Buffer>,
  sourceMap: undefined,
  generatorOptions: Record<string, any>,
) => Promise<{
  code: string | Buffer;
  filename?: string;
  errors?: (Error | string)[];
  warnings?: (Error | string)[];
}>;

type generate = generateFn | generateFn[];

Default: undefined

Rewrites a module's own bytes as it is built, rather than an asset after the build. That is the one point at which a re-encoding can also rename — return a filename and the asset is emitted under it, with every reference in the bundle following. minify cannot: an asset's name is decided during code generation, so renaming there would leave the bundle pointing at a URL nothing emits.

test, include and exclude select which modules it sees, matched against the module's resource — query and all, so ?as=webp is matchable. A generator runs in the webpack process, since modules build before the worker pool is up, and its answer is cached under the bytes plus the generator and its options.

Two generators ship with the plugin, and they differ in who picks the format. sharpGenerate is told: it takes the target from the request's ?as= or, failing that, from a generatorOptions.encodeOptions naming exactly one format, and reports an error when neither says which format to write. imageminGenerate is not: its plugins decide, so it reads the format back off the bytes they produced and renames to match, leaving an asset its plugins did not convert under the name it had.

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  module: {
    rules: [
      {
        test: /\.(jpe?g|png)$/i,
        type: "asset/resource",
        // The query has to survive into the name, or two formats of one image
        // collide.
        generator: { filename: "[name][ext][query]" },
      },
    ],
  },
  plugins: [
    new MinimizerPlugin({
      test: /\.(jpe?g|png)$/i,
      generate: MinimizerPlugin.sharpGenerate,
    }),
  ],
};
// `image.jpg` is emitted as `image.webp`, and this import points at it.
import webp from "./image.jpg?as=webp";

In watch mode the rename is carried on the module rather than reapplied each build, so a rebuild that does not touch the image keeps pointing at the generated name without running the generator again. Changing the image does run it again, since its answer is cached under the bytes.

The same holds across runs under cache.type: "filesystem", where a module is restored from the pack rather than rebuilt. That restored result is the generator's, so changing generate or generatorOptions has to invalidate the pack, and the plugin adds their identity to cache.version so it does. This needs the plugin to be in the config — plugins or optimization.minimizer — since webpack builds the cache while it applies them; a plugin applied by hand after webpack() returns is too late to reach it, and a changed generator would then be ignored until the cache directory is removed.

Note

generate needs a webpack whose NormalModule processResult hook can be awaited (5.111 or newer). On an older webpack the plugin reports an error rather than silently generating nothing.

generatorOptions

Type:

type generatorOptions = Record<string, any> | Record<string, any>[];

Default: {}

Options for generate, exactly as minimizerOptions is for minify: one object for one generator, or an array positionally matching an array of generators. A single object handed an array of generators is reused for every one of them.

ecma is filled in from output.environment unless the options set it, the same way it is for minimizerOptions.

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  plugins: [
    new MinimizerPlugin({
      test: /\.(jpe?g|png)$/i,
      generate: MinimizerPlugin.sharpGenerate,
      // Names the format when the request does not, and carries the encoder's
      // own settings either way.
      generatorOptions: { encodeOptions: { webp: { quality: 90 } } },
    }),
  ],
};

extractComments

Type:

type extractComments =
  | boolean
  | string
  | RegExp
  | ((
      astNode: any,
      comment: {
        value: string;
        type: "comment1" | "comment2" | "comment3" | "comment4";
        pos: number;
        line: number;
        col: number;
      },
    ) => boolean)
  | {
      condition?:
        | boolean
        | "all"
        | "some"
        | RegExp
        | ((
            astNode: any,
            comment: {
              value: string;
              type: "comment1" | "comment2" | "comment3" | "comment4";
              pos: number;
              line: number;
              col: number;
            },
          ) => boolean)
        | undefined;
      filename?: string | ((fileData: any) => string) | undefined;
      banner?:
        string | boolean | ((commentsFile: string) => string) | undefined;
    };

Default: true

Whether comments shall be extracted to a separate file, (see details).

By default, extract only comments using /^\**!|@preserve|@license|@cc_on/i RegExp condition and remove remaining comments.

If the original file is named foo.js, then the comments will be stored to foo.js.LICENSE.txt.

The minimizerOptions.format.comments option specifies whether the comment will be preserved - i.e., it is possible to preserve some comments (e.g. annotations) while extracting others, or even preserve comments that have already been extracted.

boolean

Enable/disable extracting comments.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        extractComments: true,
      }),
    ],
  },
};

string

Extract all or some (use the /^\**!|@preserve|@license|@cc_on/i RegExp) comments.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        extractComments: "all",
      }),
    ],
  },
};

RegExp

All comments that match the given expression will be extracted to a separate file.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        extractComments: /@extract/i,
      }),
    ],
  },
};

function

All comments that match the given expression will be extracted to a separate file.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        extractComments: (astNode, comment) => {
          if (/@extract/i.test(comment.value)) {
            return true;
          }

          return false;
        },
      }),
    ],
  },
};

object

Allows you to customize condition for extracting comments, and specify the extracted file name and banner.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        extractComments: {
          condition: /^\**!|@preserve|@license|@cc_on/i,
          filename: (fileData) =>
            // The "fileData" argument contains object with "filename", "basename", "query" and "hash"
            `${fileData.filename}.LICENSE.txt${fileData.query}`,
          banner: (licenseFile) =>
            `License information can be found in ${licenseFile}`,
        },
      }),
    ],
  },
};
condition

Type:

type condition =
  | boolean
  | "all"
  | "some"
  | RegExp
  | ((
      astNode: any,
      comment: {
        value: string;
        type: "comment1" | "comment2" | "comment3" | "comment4";
        pos: number;
        line: number;
        col: number;
      },
    ) => boolean)
  | undefined;

The condition that determines which comments should be extracted.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        extractComments: {
          condition: "some",
          filename: (fileData) =>
            // The "fileData" argument contains object with "filename", "basename", "query" and "hash"
            `${fileData.filename}.LICENSE.txt${fileData.query}`,
          banner: (licenseFile) =>
            `License information can be found in ${licenseFile}`,
        },
      }),
    ],
  },
};
filename

Type:

type filename = string | ((fileData: any) => string) | undefined;

Default: [file].LICENSE.txt[query]

Available placeholders: [file], [query] and [filebase] ([base] for webpack 5).

The file where the extracted comments will be stored.

Default is to append the suffix .LICENSE.txt to the original filename.

Warning

We highly recommend using the .txt extension. Using .js/.cjs/.mjs extensions may conflict with existing assets, which leads to broken code.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        extractComments: {
          condition: /^\**!|@preserve|@license|@cc_on/i,
          filename: "extracted-comments.js",
          banner: (licenseFile) =>
            `License information can be found in ${licenseFile}`,
        },
      }),
    ],
  },
};
banner

Type:

type banner = string | boolean | ((commentsFile: string) => string) | undefined;

Default: /*! For license information please see ${commentsFile} */

The banner text that points to the extracted file and will be added at the top of the original file.

It can be false (no banner), a String, or a function<(string) -> String> that will be called with the filename where the extracted comments have been stored.

The banner will be wrapped in a comment.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        extractComments: {
          condition: true,
          filename: (fileData) =>
            // The "fileData" argument contains object with "filename", "basename", "query" and "hash"
            `${fileData.filename}.LICENSE.txt${fileData.query}`,
          banner: (commentsFile) =>
            `My custom banner about license information ${commentsFile}`,
        },
      }),
    ],
  },
};

Embedded source

Source written in one language that reaches the bundle inside another is minified too, which no asset carries and an asset-level minimizer therefore never sees. It needs no option (webpack >= 5.110.0; older versions reach only what an asset nests inside itself).

Such source has no filename, so test / include / exclude and each minimizer's filter — all of which match filenames — cannot dispatch it. It is dispatched by the language it is written in, which every minify function states for itself:

myCssMinifier.getTypes = () => ["css"];

The built-ins declare javascript (terserMinify, uglifyJsMinify, swcMinify, esbuildMinify), css (cssnanoMinify, cssoMinify, cleanCssMinify, esbuildMinifyCss, lightningCssMinify, swcMinifyCss), html (htmlMinifierTerser, swcMinifyHtml, swcMinifyHtmlFragment, minifyHtmlNode) and json (jsonMinify); webpack's own cssMinify and htmlMinify declare css and html. A language no configured minimizer claims — svg out of the box — is emitted exactly as it was written, and a custom minify function without getTypes is never handed embedded source at all.

What this reaches:

  • CSS and HTML a module embeds in a JavaScript string literal (every exportType but link).
  • The text an asset/source module embeds, and the payload an asset/inline module encodes — the payload before it is encoded, so the encoding covers what came back.
  • What a document or a stylesheet nests inside itself: an inline <style>, every style="", a <script> holding JavaScript or JSON, an <svg> subtree, the document an <iframe srcdoc> holds, and the payload of a url() data: URL. This is how an inline <script> is minified by terser at all.

A style="" arrives as css with as: "block-contents" — the same word module.parser.css.as uses. It holds a block's contents rather than a whole stylesheet, so a minifier claiming css is handed one either way and as says which it is. Ignore it at your peril: parsing a declaration list as a stylesheet finds no rule and returns nothing.

The nested case needs a minifier that can hand its nested bodies out, which it also states for itself — webpack's cssMinify and htmlMinify do:

// The languages this minifier can offer, given the options it will run with.
myHtmlMinifier.getEmbeddedTypes = (minimizerOptions) => ["css", "javascript"];

The option is passed only when the two declarations meet: if nothing configured claims a language this minifier could offer, it is never handed one, and minification is exactly what it always was. When it is, the nested bodies are reached in the same parse that prints — the minifier leaves a marker where each one goes and the answers are put in their place, so nothing is parsed twice.

Note

Source a module embeds in JavaScript is minified during code generation, before the worker pool is up, so parallel does not apply to it. What an asset nests inside itself is minified in the pool with the asset.

Examples

Preserve Comments

Extract all legal comments (i.e. /^\**!|@preserve|@license|@cc_on/i) and preserve /@license/i comments.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minimizerOptions: {
          format: {
            comments: /@license/i,
          },
        },
        extractComments: true,
      }),
    ],
  },
};

Remove Comments

If you want to build without comments, use this config:

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minimizerOptions: {
          format: {
            comments: false,
          },
        },
        extractComments: false,
      }),
    ],
  },
};

uglify-js

UglifyJS is a JavaScript parser, minifier, compressor and beautifier toolkit.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minify: MinimizerPlugin.uglifyJsMinify,
        // `minimizerOptions` will be passed to `uglify-js`
        // Link to options - https://github.com/mishoo/UglifyJS#minify-options
        minimizerOptions: {},
      }),
    ],
  },
};

swc

swc is a super-fast compiler written in Rust, producing widely supported JavaScript from modern standards and TypeScript.

Warning

extractComments is supported with @swc/core >= 1.15.30. Only serializable extract conditions are supported: booleans, "some", "all", string patterns, RegExp values without flags, or object conditions that resolve to those forms. Function conditions and flagged regular expressions are not supported.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minify: MinimizerPlugin.swcMinify,
        // `minimizerOptions` will be passed to `swc` (`@swc/core`)
        // Link to options - https://swc.rs/docs/config-js-minify
        minimizerOptions: {},
      }),
    ],
  },
};

esbuild

esbuild is an extremely fast JavaScript bundler and minifier.

Warning

The extractComments option is not supported, and all legal comments (i.e. copyright, licenses and etc) will be preserved.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minify: MinimizerPlugin.esbuildMinify,
        // `minimizerOptions` will be passed to `esbuild`
        // Link to options - https://esbuild.github.io/api/#minify
        // Note: the `minify` options is true by default (and override other `minify*` options), so if you want to disable the `minifyIdentifiers` option (or other `minify*` options) please use:
        // minimizerOptions: {
        //   minify: false,
        //   minifyWhitespace: true,
        //   minifyIdentifiers: false,
        //   minifySyntax: true,
        // },
        minimizerOptions: {},
      }),
    ],
  },
};

JSON

Uses JSON.stringify() to minify your JSON files during the build process.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      // Keeps original terser plugin to minify JS files
      "...",
      // Will minify JSON files (they can come from copy-webpack-plugin or when you are using asset modules)
      new MinimizerPlugin({
        test: /\.json$/,
        minify: MinimizerPlugin.jsonMinify,
        // We are supporting `space` and `replacer` options, you can set them below
        minimizerOptions: {},
      }),
    ],
  },
};

HTML

The plugin can minify HTML assets too. Pick one of the bundled HTML minimizers and set test to match your HTML files.

Available HTML minimizers:

  • MinimizerPlugin.htmlMinifierTerser — uses html-minifier-terser.
  • MinimizerPlugin.swcMinifyHtml — uses @swc/html for full HTML documents (with doctype and <html>/<head>/<body> tags).
  • MinimizerPlugin.swcMinifyHtmlFragment — uses @swc/html for HTML fragments (e.g. content inside <template></template> or partial HTML strings).
  • MinimizerPlugin.minifyHtmlNode — uses @minify-html/node.
  • webpack.html.syntax.htmlMinify — webpack's own HTML minifier, shipped with webpack itself. See webpack's own minimizers.

The HTML minimizers are optional peer dependencies — install only the one you actually use:

npm install --save-dev html-minifier-terser
# or
npm install --save-dev @swc/html
# or
npm install --save-dev @minify-html/node

Note

HTML assets typically come from plugins like copy-webpack-plugin, html-webpack-plugin, or webpack's asset modules.

Note

Whitespace handling differs between tools (defaults):

  • @swc/html — removes/collapses whitespace only in safe places (around html/body, inside <head>, between <meta>/<script>/<link> etc.).
  • html-minifier-terser — always collapses multiple whitespaces to a single space (never removes entirely); configurable via its options.
  • @minify-html/node — see its whitespace docs.

html-minifier-terser

html-minifier-terser is a JavaScript-based HTML minifier with no native dependency. It's the default HTML minimizer.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      // Keeps the default Terser plugin for JS files
      "...",
      new MinimizerPlugin({
        test: /\.html(\?.*)?$/i,
        minify: MinimizerPlugin.htmlMinifierTerser,
        // Options - https://github.com/terser/html-minifier-terser#options-quick-reference
        minimizerOptions: {
          collapseWhitespace: true,
          removeComments: true,
        },
      }),
    ],
  },
};

@swc/html — HTML documents

Use swcMinifyHtml for complete HTML documents (i.e. with a doctype and <html>/<head>/<body> tags).

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.html(\?.*)?$/i,
        minify: MinimizerPlugin.swcMinifyHtml,
        // Options - https://github.com/swc-project/bindings/blob/main/packages/html/index.ts
        minimizerOptions: {},
      }),
    ],
  },
};

@swc/html — HTML fragments

Use swcMinifyHtmlFragment for partial HTML — for example, content of <template></template> tags or HTML strings that get injected into another document.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.template\.html$/i,
        minify: MinimizerPlugin.swcMinifyHtmlFragment,
        // Options - https://github.com/swc-project/bindings/blob/main/packages/html/index.ts
        minimizerOptions: {},
      }),
    ],
  },
};

Note

The difference between swcMinifyHtml and swcMinifyHtmlFragment is the error reporting — invalid or broken syntax is reported at build time.

@minify-html/node

@minify-html/node is a Rust HTML minifier.

webpack.config.js

const Minimizer = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new Minimizer({
        test: /\.html(\?.*)?$/i,
        minify: Minimizer.minifyHtmlNode,
        // Options - https://github.com/wilsonzlin/minify-html#minification
        minimizerOptions: {},
      }),
    ],
  },
};

You can also stack multiple MinimizerPlugin instances to compress different files with different minify functions in the same build (e.g. JS with terserMinify, HTML with htmlMinifierTerser, JSON with jsonMinify).

CSS

The plugin can minify CSS assets too. Pick one of the bundled CSS minimizers and set test to match your CSS files.

Available CSS minimizers:

  • MinimizerPlugin.cssnanoMinify — uses cssnano (via postcss).
  • MinimizerPlugin.cssoMinify — uses csso.
  • MinimizerPlugin.cleanCssMinify — uses clean-css.
  • MinimizerPlugin.esbuildMinifyCss — uses esbuild with the CSS loader.
  • MinimizerPlugin.lightningCssMinify — uses lightningcss.
  • MinimizerPlugin.swcMinifyCss — uses @swc/css.
  • webpack.css.syntax.cssMinify — webpack's own CSS minifier, shipped with webpack itself. See webpack's own minimizers.

The CSS minimizers are optional peer dependencies — install only the ones you actually use:

npm install --save-dev cssnano postcss
# or
npm install --save-dev csso
# or
npm install --save-dev clean-css
# or
npm install --save-dev esbuild
# or
npm install --save-dev lightningcss
# or
npm install --save-dev @swc/css

Note

CSS assets typically come from plugins like mini-css-extract-plugin or webpack's asset modules.

cssnano

cssnano is the default CSS minimizer. It runs as a PostCSS plugin.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      // Keeps the default Terser plugin for JS files
      "...",
      new MinimizerPlugin({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.cssnanoMinify,
        // Options - https://cssnano.github.io/cssnano/docs/config-file/
        minimizerOptions: {
          preset: "default",
        },
      }),
    ],
  },
};

csso

csso is a CSS minifier with structural optimisations.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.cssoMinify,
        // Options - https://github.com/css/csso#minifysource-options
        minimizerOptions: {},
      }),
    ],
  },
};

clean-css

clean-css is a widely-used CSS optimiser.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.cleanCssMinify,
        // Options - https://github.com/clean-css/clean-css#constructor-options
        minimizerOptions: {},
      }),
    ],
  },
};

esbuild

esbuild ships with a fast CSS minifier (used via its CSS loader).

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.esbuildMinifyCss,
        // Options - https://esbuild.github.io/api/#transform-api
        minimizerOptions: {},
      }),
    ],
  },
};

lightningcss

lightningcss is a Rust-based CSS parser, transformer, and minifier.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.lightningCssMinify,
        // Options - https://lightningcss.dev/transpilation.html
        minimizerOptions: {},
      }),
    ],
  },
};

@swc/css

@swc/css is a Rust-based CSS minifier.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.swcMinifyCss,
        // Options - https://github.com/swc-project/bindings/blob/main/packages/css/index.ts
        minimizerOptions: {},
      }),
    ],
  },
};

webpack's own minimizers

webpack ships a CSS and an HTML minimizer of its own. They need no extra dependency — if you have webpack, you have them — and they are the two that can hand out what a document or a stylesheet nests inside itself, so pairing them with terserMinify and jsonMinify is what minifies embedded source (see Embedded source). They are reached through webpack's public css.syntax and html.syntax exports, and need webpack 5.111.0 or newer.

const MinimizerPlugin = require("minimizer-webpack-plugin");
const { cssMinify } = require("webpack").css.syntax;
const { htmlMinify } = require("webpack").html.syntax;

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        test: /\.(?:[cm]?js|css|html|json)(\?.*)?$/i,
        minify: [
          MinimizerPlugin.terserMinify,
          cssMinify,
          htmlMinify,
          MinimizerPlugin.jsonMinify,
        ],
        // Positional: one entry per `minify` entry, in the same order.
        minimizerOptions: [{}, {}, {}, {}],
      }),
    ],
  },
};

Each one dispatches itself, so test only has to be wide enough to let the assets through: cssMinify claims *.css and htmlMinify claims *.html through their own filter, and both run in the worker pool.

cssMinify htmlMinify
getTypes() css html
getEmbeddedTypes() svg, css, html, json, javascript css, javascript, json, svg, html
filter /\.css(\?.*)?$/i /\.html(\?.*)?$/i
supportsWorkerThreads() true true

minimizerOptions is optimization.minimize.css and optimization.minimize.html respectively. environment carries what the target can read ({ browsers, vendorPrefixes }, the CSS entries of output.environment), so a spelling the target could not parse is never reached for.

cssMinify options

Every option is named directly on the object — the per-transform switches sit beside the rest, not nested.

Option Type Default What it does
environment { browsers?: string[], vendorPrefixes?: boolean } — What the target can read. browsers is a browserslist selection; vendorPrefixes: false leaves prefixes alone.
as "stylesheet" | "block-contents" "stylesheet" Which production to read the source as. The plugin sets it — a style="" arrives as "block-contents".
convertLengthUnits boolean false Rewrite a length into a shorter unit it is exactly equal in (16px → 1pc). Off because it earns nothing once compressed.
rewriteCustomProperties boolean false Shorten a custom property's value like any other (--x:#ffffff → --x:#fff). Off because getPropertyValue() hands that text back.
unusedSymbols string[] — Names a whole-project analysis found unused; a bare name is a class, id or @keyframes, a ---prefixed one a custom property.
pseudoClasses { [name: string]: string } — Write a pseudo-class as a class instead, so a script can apply it where the engine does not.
renderEmbeddedSource function — Owned by the plugin — do not pass it.

Per-transform switches, each on unless set to false:

Switch What it rewrites
colorFallbacks Writes a color the target cannot read as an extra declaration before it, in a spelling it does read.
lowerUnsupported Writes a spelling the target cannot read as one it can — the same value, said another way.
foldCase Lowercases a name that matches ASCII case-insensitively (at-rule, property, pseudo, function, unit, keyword).
rewriteEscapes Writes an escaped identifier the shortest way that names it.
comments Which comments survive: "some" (default), true / "all", false, or a pattern / predicate over the comment's text.
resolveCustomAtRules Inlines what @custom-media / @custom-selector names, and drops the rule that named it.
mergeLonghands Writes a family of longhands as the one shorthand that sets them.
mergeRules Joins rules printing the same block, at-rules sharing a prelude, and a @layer block a later sibling reopens.
normalizeQuotes Normalizes quoting of strings, url(), font families and attribute values.
reduceFunctions Computes a call into the shorter call naming the same value (calc(), transforms, gradients, easings, filters).
removeDeadRules Drops a rule or declaration nothing can read — an empty rule, one an identical later one supersedes.
rewriteDirSelector Writes a :dir() the target cannot read as the [dir] attribute selector.
shortenColors Writes each color in the shortest spelling of the same value.
shortenMediaQueries Writes a media feature in its range spelling and collapses an and of two into the interval.
shortenNumbers Writes each number in its shortest equal spelling.
shortenSelectors Rewrites a selector into a shorter equal one.
shortenValues Writes a value the shortest way its property's own grammar allows.

htmlMinify options

Option Type Default What it does
environment same as cssMinify — CSS's, not HTML's: handed to the CSS minifier this runs over inline CSS.
css object {} The CSS minifier's options for that inline CSS — see below.
collapseWhitespace boolean | "conservative" | "smart" | "all" false Collapses each run of whitespace in text, except where an ancestor renders it verbatim; "smart" also drops what sits against a block edge, "all" every edge.
removeEmptyAttributes boolean false Drops an attribute whose empty value leaves it in the state its absence gives.
removeEmptyElements boolean false Drops an element with no children and no attributes, unless its bare form is meaningful.
mergeStyles boolean false Prints a run of adjacent <style> elements as one sheet.
sortAttributes boolean false Prints attributes commonest name first, ties by name — nothing in HTML reads the order.
sortTokenLists boolean false Prints every token list the DOM reads as a set (class, rel, part, …) in token order.
removeRedundantAttributes boolean | "smart" | "all" false Drops an attribute whose value is the element's own default; "all" also drops spec defaults a selector can match.
removeImpliedTags boolean | "smart" | "all" "smart" How much of the <html> / <head> / <body> shell may be left out: "smart" only the <html> start tag, true / "all" all six.
minifyConditionalComments boolean false Minifies the markup inside a conditional comment's body.
renderEmbeddedSource function — Owned by the plugin — do not pass it.

Per-transform switches, each on unless set to false:

Switch What it rewrites
collapseBooleanAttributes Writes a boolean attribute spelled with its own name (disabled="disabled") as the bare name.
comments Which comments survive — same values as CSS's. One a parser or server reads is kept regardless.
normalizeAttributeQuotes Drops or re-picks an attribute value's quotes.
normalizeEnumeratedAttributes Folds an enumerated value to the keyword it names.
normalizeListAttributes Normalizes a space-, comma- or descriptor-separated list (class, rel, srcset, sizes, viewport content).
normalizeNumericAttributes Writes an integer attribute the one way its rules read it.
removeOptionalTags Leaves out an optional tag other than the shell, which is removeImpliedTags.

The css object takes the CSS minifier's convertLengthUnits, rewriteCustomProperties, unusedSymbols and pseudoClasses, plus the CSS per-transform switches. environment is not among them: htmlMinify runs the CSS minifier over every inline <style> and style="", so environment stays top level, shared by the document and the CSS inside it. Give the two minimizers the same environment and a .css asset and the same declaration inline agree about the target:

const environment = { browsers: ["chrome 100", "safari 15"] };

const minimizerOptions = [
  {},
  // cssMinify
  { environment, convertLengthUnits: true },
  // htmlMinify — `environment` reaches the CSS it nests; `css` carries the rest
  { environment, css: { convertLengthUnits: true } },
  {},
];

Note

Do not pass renderEmbeddedSource yourself. The plugin owns that option: it wires the minimizers to each other with it, and a value you set is replaced. What a minimizer offers and what another claims is what routes embedded source — see Embedded source.

Both minimizers re-resolve webpack when they run, in the worker pool as well as in the main process, so the webpack resolvable from this plugin has to be the one they came from, and at least 5.111.0 — the release that exports them on webpack.css.syntax and webpack.html.syntax. On an older webpack the destructure above yields undefined; a second or older copy in the tree surfaces from inside the minifier as:

Cannot destructure property 'SourceProcessor' of 'webpack.css.syntax' as it is undefined.
Cannot destructure property 'askEmbeddedRenderer' of 'webpack.html.syntax' as it is undefined.

Deduplicate webpack (npm dedupe, or a single version in a workspace root) and it goes away.

Images

The plugin can minify image assets too. Pick one of the bundled image minimizers and set test to match your images.

Available image minimizers:

  • MinimizerPlugin.sharpMinify — uses sharp, re-encoding each image as its own format.
  • MinimizerPlugin.svgoMinify — uses svgo.
  • MinimizerPlugin.imageminMinify — uses imagemin and the plugins you name.
  • MinimizerPlugin.napiRsImageMinify — uses @napi-rs/image, which ships prebuilt codecs.

Converting an image to another format is generate's job rather than a minimizer's, since only that can rename the asset: MinimizerPlugin.sharpGenerate and MinimizerPlugin.imageminGenerate.

The image minimizers are optional peer dependencies — install only the ones you actually use:

npm install --save-dev sharp
# or
npm install --save-dev svgo
# or
npm install --save-dev imagemin imagemin-mozjpeg imagemin-pngquant

Note

On minify these only minify — they never change an image's format or name. An asset's name is decided during code generation, long before a minimizer runs, so a renamed asset would leave the bundle pointing at a URL nothing emits. Converting .png to .webp is what generate is for: it runs while the module builds, early enough to rename.

Note

sharp and imagemin read the asset's bytes rather than its text, so they run in the webpack process rather than in the worker pool — they do their own threading. Minimizers configured beside them keep the pool.

Lossless and lossy

Images are optimized in one of two modes:

  1. Lossless — the decoded pixels come back identical, only the encoding is made smaller.
  2. Lossy — quality is traded for a smaller file.

Which one you get with no encodeOptions at all, measured by decoding the output back to pixels and comparing it with the input:

Format sharpMinify napiRsImageMinify
avif lossy lossy
gif lossy not handled
jpeg lossy lossless
png lossless lossless
tiff lossy not handled
webp lossy lossy

So sharpMinify is lossy by default everywhere except PNG — it re-encodes at sharp's own defaults, which are quality settings rather than lossless ones. napiRsImageMinify is lossless by default for both PNG and JPEG, because those two are repacked in place by oxipng and mozjpeg, rewriting the encoded bytes rather than decoding to pixels and encoding again.

svgoMinify rewrites markup rather than pixels. It is lossless in the sense that the rendered image is meant to be unchanged, but its default plugin preset does rewrite paths and drop metadata — see svgo for which of those to turn off.

imageminMinify is whatever its plugins are. imagemin-jpegtran, imagemin-optipng and imagemin-gifsicle are lossless; imagemin-mozjpeg and imagemin-pngquant are lossy. imagemin-svgo can be either.

Asking sharpMinify for lossless output

new MinimizerPlugin({
  test: /\.(png|jpe?g|webp|avif)(\?.*)?$/i,
  minify: MinimizerPlugin.sharpMinify,
  minimizerOptions: {
    encodeOptions: {
      // https://sharp.pixelplumbing.com/api-output
      jpeg: { quality: 100 },
      webp: { lossless: true },
      avif: { lossless: true },
      // PNG is already lossless at sharp's defaults
      png: {},
    },
  },
});

Asking napiRsImageMinify for lossy output, which is where the savings are:

new MinimizerPlugin({
  test: /\.(png|jpe?g|webp|avif)(\?.*)?$/i,
  minify: MinimizerPlugin.napiRsImageMinify,
  minimizerOptions: {
    encodeOptions: {
      // Anything below 100 re-encodes rather than repacking
      jpeg: { quality: 80 },
      webp: { quality: 80 },
      avif: { quality: 70 },
      // `png` has no quality setting — it is lossless either way
    },
  },
});

Note

Lossless does not mean "no smaller". On this repository's own PNG fixture napiRsImageMinify returns 59% of the original size without touching a single pixel, and sharpMinify returns 92%.

sharp

sharp re-encodes each image as the format its name already claims, so a .png stays a PNG. It handles avif, gif, heif, jp2, jpeg, png, tiff and webp.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      // Keeps the default Terser plugin for JS files
      "...",
      new MinimizerPlugin({
        test: /\.(png|jpe?g|webp|avif|tiff?|gif)$/i,
        minify: MinimizerPlugin.sharpMinify,
        minimizerOptions: {
          // Options are keyed by sharp's format name
          // https://sharp.pixelplumbing.com/api-output
          encodeOptions: {
            jpeg: { quality: 80 },
            png: { compressionLevel: 9 },
            webp: { lossless: true },
          },
        },
      }),
    ],
  },
};

sharp can also transform the image while it re-encodes:

new MinimizerPlugin({
  test: /\.(png|jpe?g)$/i,
  minify: MinimizerPlugin.sharpMinify,
  minimizerOptions: {
    // `enabled` and `unit` ("px" by default, or "percent") are read here;
    // everything else goes to sharp
    // https://sharp.pixelplumbing.com/api-resize
    resize: { width: 800, unit: "px", fit: "inside" },
    // A number of degrees, or "auto" to follow the EXIF orientation
    rotate: "auto",
    flip: false,
    flop: false,
    grayscale: false,
    // A sigma, or true for a fast default
    blur: false,
    sharpen: false,
    encodeOptions: { jpeg: { quality: 80 } },
  },
});

Each of these can also be asked for by an asset's own name — see Query strings in asset names.

svgo

svgo minifies SVG. It also reaches an asset/inline SVG — one that becomes a data: URI rather than a file — which carries no asset name for test to match; see Embedded source.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.svg(\?.*)?$/i,
        minify: MinimizerPlugin.svgoMinify,
        minimizerOptions: {
          // Options - https://github.com/svg/svgo#configuration
          encodeOptions: {
            multipass: true,
            plugins: ["preset-default"],
          },
        },
      }),
    ],
  },
};

imagemin

imagemin runs the plugins you name. Each is a string — "mozjpeg" resolves imagemin-mozjpeg — or a [name, options] pair. Install each plugin yourself.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.(png|jpe?g|gif|svg)$/i,
        minify: MinimizerPlugin.imageminMinify,
        minimizerOptions: {
          plugins: [
            "gifsicle",
            "mozjpeg",
            ["pngquant", { quality: [0.6, 0.8] }],
            "svgo",
          ],
        },
      }),
    ],
  },
};

Note

A plugin that converts — imagemin-webp, imagemin-avif — writes a format the asset's name does not claim. imageminMinify keeps the original and warns instead of writing it, since it cannot rename the asset. Reach for generate with MinimizerPlugin.imageminGenerate to convert: it runs the same plugins while the module builds, which is where the asset can still take the name of the format they wrote.

@napi-rs/image

@napi-rs/image is a set of Rust codecs shipped as prebuilt binaries, so it needs no system library. It handles avif, jpeg, png and webp — the formats it both reads back reliably and makes smaller.

Each format is re-encoded as itself, using the codec that does that best: png goes through oxipng, which rewrites the container losslessly and leaves the pixels untouched, and jpeg through mozjpeg. Decoding either to pixels and re-encoding saves a small fraction as much.

webpack.config.js

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      "...",
      new MinimizerPlugin({
        test: /\.(png|jpe?g|webp|avif)$/i,
        minify: MinimizerPlugin.napiRsImageMinify,
        minimizerOptions: {
          // Options are keyed by the format's own name
          // https://github.com/Brooooooklyn/Image#usage
          encodeOptions: {
            // `PNGLosslessOptions`
            png: { force: true },
            // `JpegCompressOptions`
            jpeg: { quality: 80 },
            // `AvifConfig`
            avif: { quality: 70, speed: 4 },
            // The quality factor, 0-100
            webp: { quality: 80 },
          },
        },
      }),
    ],
  },
};

Note

png is recompressed losslessly, so it takes no quality setting. Resizing and rotating are not exposed here — use sharp for those.

Query strings in asset names

An asset keeps the query and fragment of the request that made it: output.assetModuleFilename is [hash][ext][query][fragment] by default, so import icon from "./icon.svg?v=2" is emitted as <hash>.svg?v=2.

test, include and exclude are read against both spellings — the whole name and the name with the query and fragment stripped — so all three of these accept that asset:

test: /\.svg$/i; // names the file
test: /\.svg(\?.*)?$/i; // names the query form
test: /\?v=2$/; // names the query itself

exclude rejects on either spelling, so excluding by file name also excludes the queried asset. Every built-in minimizer's own filter reads past the query in the same way.

Asking sharp for something from the import. sharpMinify reads what to do off the asset's name, so one image can be sized, turned or re-encoded where it is imported rather than in the configuration:

import banner from "./banner.png?width=320&quality=80";
Query Short Value What it does
width w pixels, or auto target width
height h pixels, or auto target height
unit u px (default) or percent how width and height are read
fit cover (default), contain, fill, … what to do when both dimensions are given
position pos centre (default), right top, entropy, … where to crop from
background bg a colour what contain pads with
without-enlargement flag never scale the image up
rotate rot degrees, or auto turn by an angle, or by the EXIF orientation
flip flag mirror vertically
flop flag mirror horizontally
grayscale gray flag drop the colour
blur sigma, or flag blur
sharpen sigma, or flag sharpen
quality q a number encode quality
lossless flag encode losslessly, where the format has one
effort a number how hard the encoder tries
progressive prog flag interlace, where the format has it
Import What comes out
./photo.jpg?w=64&h=64&fit=cover&pos=entropy a 64x64 thumbnail, cropped to the busiest part
./photo.jpg?width=16&blur&quality=30 a tiny blurred placeholder
./logo.png?width=50&unit=percent&grayscale half-size and grey

A flag is on when it is present — ?flip — and reads true/1/yes the same way, false/0/no the other. greyscale and grey spell grayscale, auto on width or height drops one set in minimizerOptions, and a parameter can be spelled in any case.

Every one of these can also be set in minimizerOptions; the name wins where both say something, being the more specific of the two. resize: { enabled: false } still turns resizing off entirely.

Two rules decide what happens to a value:

  • Its shape is checked here, and anything else is ignored. An asset's name carries queries this plugin never put there, so ?v=2 must not become a resize — and neither does ?width=nonsense or ?flip=maybe.
  • Whether a well-formed value is one sharp accepts is sharp's to report, and it answers per format: effort runs to 6 for webp and 9 for avif, quality starts at 0 for png and 1 for jpeg, and a colour is whatever it can parse. A value outside those fails the build with sharp's own message rather than being dropped silently. An option a format has no use for — ?lossless on a jpeg — is simply ignored.

napiRsImageMinify reads the same names, as far as @napi-rs/image goes: width/w, height/h, fit (cover, fill, inside), filter (nearest, triangle, catmull-rom, gaussian, lanczos3), rotate/rot, flip, flop, grayscale, invert, blur, quality/q, lossless and speed. Three differences are worth knowing:

  • rotate takes a quarter turn, not any angle — 90, 180, 270, a negative or a multiple of those, or auto for the EXIF orientation. napi applies one orientation, so mirroring and a turn compose into it (?flip&flop is a half turn); asking for auto alongside an explicit turn warns, because only one of them can be applied.
  • Every value is checked here, rather than left to the library as sharp's are. napi rejects an unknown fit without naming it, and answers a quality of 150 by silently writing a bigger file, so a value it would mishandle is dropped instead.
  • Transforming costs the repack. This minimizer's advantage is rewriting encoded bytes — oxipng saves 99% of a png where decoding and re-encoding saves 9% — so when a query makes a transform necessary, its output is handed back to the repack rather than replacing it. A ?rotate=auto on an image whose EXIF asks for nothing skips the decode entirely.

svgoMinify reads precision (or floatPrecision, 0–10), multipass, pretty and indent, so one SVG can be laid out readably or coarsened without a second configuration:

import icon from "./icon.svg?precision=1";

imageminMinify reads nothing. Its options are a list of already-configured plugins, each with option names of its own, so there is no parameter a query could set that would mean the same thing twice over.

Note

Two assets whose names differ only by their query would be written to the same file, and webpack refuses that. To emit several sizes of one image, give each its own file name and keep the query on the asset name:

module.exports = {
  output: {
    assetModuleFilename: (pathData) => {
      const query = pathData.module.resourceResolveData.query || "";
      const name = query.replace(/^\?/, "-").replace(/[=&]/g, "-");

      return `[name]${name}[ext][query]`;
    },
  },
};

Without the trailing [query] the size is no longer on the name and nothing resizes; without the first half the two sizes collide.

Note

A query cannot pick a format on this path. Resizing needs no new name, which is why it works here; changing the format does, and minify runs after names are decided. Hand ?as=webp to generate instead, which sees the module as it builds and can emit the new format under a new name.

Images beside everything else

minify takes an array, and each minimizer is offered only the assets its own filter accepts, so one plugin instance can cover several languages at once:

const MinimizerPlugin = require("minimizer-webpack-plugin");

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        test: /\.(js|css|svg|png|jpe?g)$/i,
        minify: [
          MinimizerPlugin.terserMinify,
          MinimizerPlugin.cssnanoMinify,
          MinimizerPlugin.svgoMinify,
          MinimizerPlugin.sharpMinify,
        ],
        // One entry per minimizer, in the same order
        minimizerOptions: [
          {},
          {},
          {},
          { encodeOptions: { png: { compressionLevel: 9 } } },
        ],
      }),
    ],
  },
};

Custom Minify Function

Override the default minify function - use uglify-js for minification.

webpack.config.js

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minify: (file, sourceMap) => {
          // https://github.com/mishoo/UglifyJS2#minify-options
          const uglifyJsOptions = {/* your `uglify-js` package options */};

          if (sourceMap) {
            uglifyJsOptions.sourceMap = {
              content: sourceMap,
            };
          }

          return require("uglify-js").minify(file, uglifyJsOptions);
        },
      }),
    ],
  },
};

Typescript

With default Terser minify function:

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin({
        minimizerOptions: {
          compress: true,
        },
      }),
    ],
  },
};

With built-in minify functions:

import { type JsMinifyOptions as SwcOptions } from "@swc/core";
import { type MinifyOptions as SwcCssOptions } from "@swc/css";
import {
  type FragmentOptions as SwcHtmlFragmentOptions,
  type Options as SwcHtmlOptions,
} from "@swc/html";
import { type OptionsOutput as CleanCssOptions } from "clean-css";
import { type Options as CssnanoOptions } from "cssnano";
import { type CompressOptions as CssoOptions } from "csso";
import { type TransformOptions as EsbuildOptions } from "esbuild";
import { type Options as HtmlMinifierTerserOptions } from "html-minifier-terser";
import { type TransformOptions as LightningCssOptions } from "lightningcss";
import { type MinifyOptions as TerserOptions } from "terser";
import { type MinifyOptions as UglifyJSOptions } from "uglify-js";

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new MinimizerPlugin<SwcOptions>({
        minify: MinimizerPlugin.swcMinify,
        minimizerOptions: {
          // `swc` options
        },
      }),
      new MinimizerPlugin<UglifyJSOptions>({
        minify: MinimizerPlugin.uglifyJsMinify,
        minimizerOptions: {
          // `uglif-js` options
        },
      }),
      new MinimizerPlugin<EsbuildOptions>({
        minify: MinimizerPlugin.esbuildMinify,
        minimizerOptions: {
          // `esbuild` options
        },
      }),

      // Alternative usage:
      new MinimizerPlugin<TerserOptions>({
        minify: MinimizerPlugin.terserMinify,
        minimizerOptions: {
          // `terser` options
        },
      }),

      // HTML minimizers
      new MinimizerPlugin<HtmlMinifierTerserOptions>({
        test: /\.html(\?.*)?$/i,
        minify: MinimizerPlugin.htmlMinifierTerser,
        minimizerOptions: {
          // `html-minifier-terser` options
        },
      }),
      new MinimizerPlugin<SwcHtmlOptions>({
        test: /\.html(\?.*)?$/i,
        minify: MinimizerPlugin.swcMinifyHtml,
        minimizerOptions: {
          // `@swc/html` options
        },
      }),
      new MinimizerPlugin<SwcHtmlFragmentOptions>({
        test: /\.template\.html$/i,
        minify: MinimizerPlugin.swcMinifyHtmlFragment,
        minimizerOptions: {
          // `@swc/html` fragment options
        },
      }),

      // CSS minimizers
      new MinimizerPlugin<CssnanoOptions>({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.cssnanoMinify,
        minimizerOptions: {
          // `cssnano` options
        },
      }),
      new MinimizerPlugin<CssoOptions>({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.cssoMinify,
        minimizerOptions: {
          // `csso` options
        },
      }),
      new MinimizerPlugin<CleanCssOptions>({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.cleanCssMinify,
        minimizerOptions: {
          // `clean-css` options
        },
      }),
      new MinimizerPlugin<EsbuildOptions>({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.esbuildMinifyCss,
        minimizerOptions: {
          // `esbuild` options (CSS loader)
        },
      }),
      new MinimizerPlugin<LightningCssOptions>({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.lightningCssMinify,
        minimizerOptions: {
          // `lightningcss` options
        },
      }),
      new MinimizerPlugin<SwcCssOptions>({
        test: /\.css(\?.*)?$/i,
        minify: MinimizerPlugin.swcMinifyCss,
        minimizerOptions: {
          // `@swc/css` options
        },
      }),
    ],
  },
};

Contributing

We welcome all contributions! If you're new here, please take a moment to review our contributing guidelines before submitting issues or pull requests.

CONTRIBUTING

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Minimizer Plugin

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