Experiments

experiments

boolean: false

experiments option was introduced in webpack 5 to empower users with the ability to activate and try out experimental features.

Available options:

• asyncWebAssembly: Support the new WebAssembly according to the updated specification, it makes a WebAssembly module an async module. And it is enabled by default when experiments.futureDefaults is set to true.
• backCompat
• buildHttp
• cacheUnaffected
• css
• futureDefaults
• layers: Enable module and chunk layers.
• lazyCompilation
• outputModule
• syncWebAssembly: Support the old WebAssembly like in webpack 4.
• topLevelAwait: Support the Top Level Await Stage 3 proposal, it makes the module an async module when await is used on the top-level. And it is enabled by default when experiments.futureDefaults is set to true.

webpack.config.js

module.exports = {
  //...
  experiments: {
    asyncWebAssembly: true,
    buildHttp: true,
    layers: true,
    lazyCompilation: true,
    outputModule: true,
    syncWebAssembly: true,
    topLevelAwait: true,
  },
};

experiments.backCompat

Enable backward-compat layer with deprecation warnings for many webpack 4 APIs.

• Type: boolean

module.exports = {
  //...
  experiments: {
    backCompat: true,
  },
};

experiments.buildHttp

When enabled, webpack can build remote resources that begin with the http(s): protocol.

• Type:

  • (string | RegExp | ((uri: string) => boolean))[]

    A shortcut for experiments.buildHttp.allowedUris.

  • HttpUriOptions

    {
      allowedUris: (string|RegExp|(uri: string) => boolean)[],
      cacheLocation?: false | string,
      frozen?: boolean,
      lockfileLocation?: string,
      upgrade?: boolean
    }

• Available: 5.49.0+

• Example

  // webpack.config.js
  module.exports = {
    //...
    experiments: {
      buildHttp: true,
    },
  };

  // src/index.js
  import pMap1 from 'https://cdn.skypack.dev/p-map';
  // with `buildHttp` enabled, webpack will build pMap1 just like a regular local module
  console.log(pMap1);

experiments.buildHttp.allowedUris

A list of allowed URIs.

• Type: (string|RegExp|(uri: string) => boolean)[]

• Example

  // webpack.config.js
  module.exports = {
    //...
    experiments: {
      buildHttp: {
        allowedUris: [
          'http://localhost:9990/',
          'https://raw.githubusercontent.com/',
        ],
      },
    },
  };

experiments.buildHttp.cacheLocation

Define the location for caching remote resources.

• Type
  • string
  • false
• Example

  // webpack.config.js
  module.exports = {
    //...
    experiments: {
      buildHttp: {
        cacheLocation: false,
      },
    },
  };

By default webpack would use <compiler-name.>webpack.lock.data/ for caching, but you can disable it by setting its value to false.

Note that you should commit files under experiments.buildHttp.cacheLocation into a version control system as no network requests will be made during the production build.

experiments.buildHttp.frozen

Freeze the remote resources and lockfile. Any modification to the lockfile or resource contents will result in an error.

• Type: boolean

experiments.buildHttp.lockfileLocation

Define the location to store the lockfile.

• Type: string

By default webpack would generate a <compiler-name.>webpack.lock file>. Make sure to commit it into a version control system. During the production build, webpack will build those modules beginning with http(s): protocol from the lockfile and caches under experiments.buildHttp.cacheLocation.

experiments.buildHttp.proxy

Specify the proxy server to use for fetching remote resources.

• Type: string

By default, Webpack would imply the proxy server to use for fetching remote resources from the http_proxy (case insensitive) environment variable. However, you can also specify one through the proxy option.

experiments.buildHttp.upgrade

Detect changes to remote resources and upgrade them automatically.

• Type: boolean

experiments.css

Enable native CSS support. Note that it's an experimental feature still under development and will be enabled by default in webpack v6, however you can track the progress on GitHub.

• Type: boolean

experiments.cacheUnaffected

Enable additional in-memory caching of modules which are unchanged and reference only unchanged modules.

• Type: boolean

Defaults to the value of futureDefaults.

experiments.futureDefaults

Use defaults of the next major webpack and show warnings in any problematic places.

webpack.config.js

module.exports = {
  //...
  experiments: {
    futureDefaults: true,
  },
};

experiments.lazyCompilation

Compile entrypoints and dynamic imports only when they are in use. It can be used for either Web or Node.js.

• Type

  • boolean

  • object

    {
    // define a custom backend
    backend?: ((
      compiler: Compiler,
      callback: (err?: Error, api?: BackendApi) => void
      ) => void)
      | ((compiler: Compiler) => Promise<BackendApi>)
      | {
        /**
         * A custom client.
        */
        client?: string;
    
        /**
         * Specify where to listen to from the server.
         */
        listen?: number | ListenOptions | ((server: typeof Server) => void);
    
        /**
         * Specify the protocol the client should use to connect to the server.
         */
        protocol?: "http" | "https";
    
        /**
         * Specify how to create the server handling the EventSource requests.
         */
        server?: ServerOptionsImport | ServerOptionsHttps | (() => typeof Server);
    
    },
    entries?: boolean,
    imports?: boolean,
    test?: string | RegExp | ((module: Module) => boolean)
    }

    • backend: Customize the backend.
    • entries: Enable lazy compilation for entries.
    • imports 5.20.0+: Enable lazy compilation for dynamic imports.
    • test 5.20.0+: Specify which imported modules should be lazily compiled.

• Available: 5.17.0+

• Example 1:

  module.exports = {
    // …
    experiments: {
      lazyCompilation: true,
    },
  };

• Example 2:

  module.exports = {
    // …
    experiments: {
      lazyCompilation: {
        // disable lazy compilation for dynamic imports
        imports: false,
  
        // disable lazy compilation for entries
        entries: false,
  
        // do not lazily compile moduleB
        test: (module) => !/moduleB/.test(module.nameForCondition()),
      },
    },
  };

experiments.outputModule

boolean

Once enabled, webpack will output ECMAScript module syntax whenever possible. For instance, import() to load chunks, ESM exports to expose chunk data, among others.

module.exports = {
  experiments: {
    outputModule: true,
  },
};