Optimization#

Rspack will select appropriate optimization configuration based on the mode. You can also customize the configuration via optimization.

optimization.removeAvailableModules#

• Type: boolean
• Default: true

A module can be removed from a Chunk if the module have been included in all of its parent Chunks.

In the above example, b.js has already been included in EntryChunk and EntryChunk2, so b.js can be removed from ChunkFoo.

optimization.moduleIds#

• Type: 'named' | 'deterministic'

optimization.chunkIds#

• Type: 'named' | 'deterministic'

optimization.minimize#

• Type: boolean
• Default: production mode istrue, development mode isfalse

Whether to minimize the bundle.

optimization.mergeDuplicateChunks#

• Type: boolean
• Default: true

Whether to merge chunks which contain the same modules. Setting optimization.mergeDuplicateChunks to false will disable this optimization.

optimization.minimizer#

• Type: Array<Plugin>
• Default: []

Customize the minimizer. When using a custom minimizer, the built-in minimizer will be disabled.

const minifyPlugin = require('@rspack/plugin-minify');
module.exports = {
  context: __dirname,
  target: 'node',
  entry: {
    main: './index.js',
  },
  optimization: {
    minimize: true,
    minimizer: [
      new minifyPlugin({
        minifier: 'terser',
      }),
    ],
  },
};

optimization.removeEmptyChunks#

• Type: boolean
• Default: true

Remove empty chunks generated in the compilation.

optimization.runtimeChunk#

• Type: boolean
• Default: true

optimization.sideEffects#

• Type: boolean | 'flag'
• Default: production mode istrue, development mode isfalse

{
  "name": "npm module",
  "version": "1.0.0",
  "sideEffects": ["**/src/*.js"]
}

Tells Rspack to recognise the sideEffects flag in package.json or rules to skip over modules which are flagged to contain no side effects when exports are not used.

optimization.sideEffects depended on builtins.treeShaking to be enabled. This configuration has a build time cost, but eliminating modules has positive impact on performance because of less code generation. Effect of this optimization depends on your codebase.

module.exports = {
  //...
  optimization: {
    sideEffects: true,
  },
};

If you only want Rspack use the manual sideEffects flag via (package.json and module.rule.sideEffects) and don't analyse code:

module.exports = {
  //...
  optimization: {
    sideEffects: 'flag',
  },
};

optimization.realContentHash#

Adds an additional hash compilation pass after the assets have been processed to get the correct asset content hashes. This feature will enable by default in production mode.

If realContentHash is set to false, internal data is used to calculate the hash and it can change when assets are identical in some cases.

module.exports = {
  //...
  optimization: {
    realContentHash: true,
  },
};

optimization.splitChunks#

• Type: false | object

Rspack supports splitting chunks with the optimization.splitChunks configuration item.

It is enabled by default for dynamically imported modules.

To turn it off, set it to false.

See details at SplitChunksPlugin.

optimization.usedExports#

• Type: boolean | 'global'
• Default: production mode istrue, development mode isfalse

Tells rspack to determine used exports for each module. This depends on optimization.providedExports. Information collected by optimization.usedExports is used by other optimizations or code generation i.e. Exports are not generated for unused exports, export names are mangled to single char identifiers when all usages are compatible. Dead code elimination in minimizers will benefit from this and can remove unused exports.

module.exports = {
  //...
  optimization: {
    usedExports: false,
  },
};

To opt-out from used exports analysis per runtime:

module.exports = {
  //...
  optimization: {
    usedExports: 'global',
  },
};

optimization.innerGraph#

• Type: boolean
• Default: production mode istrue, development mode isfalse

optimization.innerGraph tells rspack whether to conduct inner graph analysis for unused exports.

module.exports = {
  //...
  optimization: {
    innerGraph: false,
  },
};

optimization.providedExports#

• Type: boolean
• Default: true

Tells rspack to figure out which exports are provided by modules to generate more efficient code for export * from .... By default optimization.providedExports is enabled.

module.exports = {
  //...
  optimization: {
    providedExports: false,
  },
};

optimization.mangleExports#

• Type: boolean | 'deterministic' | 'size'
• Default: production mode isdeterministic, development mode isfalse

optimization.mangleExports allows to control export mangling. The following values are supported: