SplitChunksPlugin#

Default#

Out of the box SplitChunksPlugin should work well for most users.

By default it only affects on-demand chunks, because changing initial chunks would affect the script tags the HTML file should include to run the project.

Rspack will automatically split chunks based on these conditions:

• New chunk can be shared OR modules are from the node_modules folder
• New chunk would be bigger than 20kb (before min+gz)
• Maximum number of parallel requests when loading chunks on demand would be lower or equal to 30
• Maximum number of parallel requests at initial page load would be lower or equal to 30

When trying to fulfill the last two conditions, bigger chunks are preferred.

Options#

Rspack provides a set of options for developers that want more control over this functionality.

optimization.splitChunks#

This configuration object represents the default behavior of the SplitChunksPlugin.

module.exports = {
  //...
  optimization: {
    splitChunks: {
      chunks: 'async',
      minChunks: 1,
      minSize: 20000,
      maxAsyncRequests: 30,
      maxInitialRequests: 30,
      cacheGroups: {
        defaultVendors: {
          test: /[\\/]node_modules[\\/]/,
          priority: -10,
          reuseExistingChunk: true,
        },
        default: {
          minChunks: 2,
          priority: -20,
          reuseExistingChunk: true,
        },
      },
    },
  },
};

splitChunks.cacheGroups#

Cache groups can inherit and/or override any options from splitChunks.{cacheGroup}.*; but test, priority and reuseExistingChunk can only be configured on cache group level. To disable any of the default cache groups, set them to false.

module.exports = {
  //...
  optimization: {
    splitChunks: {
      cacheGroups: {
        default: false,
      },
    },
  },
};

splitChunks.chunks#

splitChunks.cacheGroups.{cacheGroup}.chunks#

• Type: 'initial' | 'all' | 'async' | RegExp | ((chunk: Chunk) => bool)
• Default: 'async'

This indicates which chunks will be selected for optimization.

When a string is provided, valid values are all, async, and initial. Providing all can be particularly powerful, because it means that chunks can be shared even between async and non-async chunks.

Alternatively, you may provide a function for more control. The return value will indicate whether to include each chunk.

You can also pass a regular expression, which is a short for (chunk) => regex.test(chunk.name).

module.exports = {
  //...
  optimization: {
    splitChunks: {
      // include all types of chunks
      chunks: 'all',
    },
  },
};

splitChunks.maxAsyncRequests#

• Type: number
• Default: 30

Maximum number of parallel requests when on-demand loading.

splitChunks.maxInitialRequests#

• Type: number
• Default: 30

Maximum number of parallel requests at an entry point.

splitChunks.minChunks#

splitChunks.cacheGroups.{cacheGroup}.minChunks#

• Type: number
• Default: 1

The minimum times must a module be shared among chunks before splitting.

splitChunks.hidePathInfo#

• Type: boolean
• Default: defaults to true if options.mode is 'production', otherwise defaults to false

Prevents exposing path info when creating names for parts splitted by maxSize.

splitChunks.minSize#

• Type: number
• Default: 20000 in production and 10000 in others

Minimum size, in bytes, for a chunk to be generated.

splitChunks.maxSize#

number = 0

Using maxSize (either globally optimization.splitChunks.maxSize per cache group optimization.splitChunks.cacheGroups[x].maxSize or for the fallback cache group optimization.splitChunks.fallbackCacheGroup.maxSize) tells Rspack to try to split chunks bigger than maxSize bytes into smaller parts. Parts will be at least minSize (next to maxSize) in size. The algorithm is deterministic and changes to the modules will only have local effects. So that it is usable when using long term caching and doesn't require records. maxSize is only a hint and could be violated when modules are bigger than maxSize or splitting would violate minSize.

When the chunk has a name already, each part will get a new name derived from that name. Depending on the value of optimization.splitChunks.hidePathInfo it will add a key derived from the first module name or a hash of it.

maxSize option is intended to be used with HTTP/2 and long term caching. It increases the request count for better caching. It could also be used to decrease the file size for faster rebuilding.

splitChunks.maxAsyncSize#

number

Like maxSize, maxAsyncSize can be applied globally (splitChunks.maxAsyncSize), to cacheGroups (splitChunks.cacheGroups.{cacheGroup}.maxAsyncSize), or to the fallback cache group (splitChunks.fallbackCacheGroup.maxAsyncSize).

The difference between maxAsyncSize and maxSize is that maxAsyncSize will only affect on-demand loading chunks.

splitChunks.maxInitialSize#

number

Like maxSize, maxInitialSize can be applied globally (splitChunks.maxInitialSize), to cacheGroups (splitChunks.cacheGroups.{cacheGroup}.maxInitialSize), or to the fallback cache group (splitChunks.fallbackCacheGroup.maxInitialSize).

The difference between maxInitialSize and maxSize is that maxInitialSize will only affect initial load chunks.

splitChunks.automaticNameDelimiter#

• Type: string
• Default: -

By default Rspack will generate names using origin and name of the chunk (e.g. vendors-main.js).

This option lets you specify the delimiter to use for the generated names.

splitChunks.name#

splitChunks.cacheGroups.{cacheGroup}.name#

• Type: string | function
• Default: false

where the version of the function type is >=0.4.1.

Also available for each cacheGroup: splitChunks.cacheGroups.{cacheGroup}.name.

The name of the split chunk. Providing false will keep the same name of the chunks so it doesn't change names unnecessarily. It is the recommended value for production builds.

Providing a string allows you to use a custom name. Specifying a string will merge all common modules and vendors into a single chunk. This might lead to bigger initial downloads and slow down page loads.

If the splitChunks.name matches an entry point name, the entry point will be removed.

splitChunks.cacheGroups#

Cache groups can inherit and/or override any options from splitChunks.*; but test, priority and reuseExistingChunk can only be configured on cache group level. To disable any of the default cache groups, set them to false.

module.exports = {
  //...
  optimization: {
    splitChunks: {
      cacheGroups: {
        default: false,
      },
    },
  },
};

splitChunks.cacheGroups.{cacheGroup}.priority#

• Type: number
• Default: -20

A module can belong to multiple cache groups. The optimization will prefer the cache group with a higher priority. The default groups have a negative priority to allow custom groups to take higher priority (default value is 0 for custom groups).

splitChunks.cacheGroups.{cacheGroup}.test#

• Type: RegExp | string | function

where the version of the function type is >=0.4.1.

Controls which modules are selected by this cache group. Omitting it selects all modules. It can match the absolute module resource path or chunk names. When a chunk name is matched, all modules in the chunk are selected.

splitChunks.cacheGroups.{cacheGroup}.enforce#

• Type: boolean

Tells Rspack to ignore splitChunks.minSize, splitChunks.minChunks, splitChunks.maxAsyncRequests and splitChunks.maxInitialRequests options and always create chunks for this cache group.

splitChunks.cacheGroups.{cacheGroup}.idHint#

• Type: string

Sets the hint for chunk id. It will be added to chunk's filename.

splitChunks.cacheGroups.{cacheGroup}.filename#

• Type: string

Allows to override the filename when and only when it's an initial chunk. All placeholders available in output.filename are also available here.

module.exports = {
  //...
  optimization: {
    splitChunks: {
      cacheGroups: {
        defaultVendors: {
          filename: 'vendors-[name].js',
        },
      },
    },
  },
};