#DeterministicModuleIdsPlugin

DeterministicModuleIdsPlugin assigns short numeric ids to modules based on their module identifiers. The ids are stable between compilations, which makes the plugin useful for long-term caching.

optimization.moduleIds: 'deterministic' uses this plugin internally. Use the plugin directly when you need to customize the deterministic id generation behavior.

import rspack from '@rspack/core';

export default {
  optimization: {
    moduleIds: false,
  },
  plugins: [
    new rspack.ids.DeterministicModuleIdsPlugin({
      maxLength: 4,
    }),
  ],
};

#Options

#context

• Type: string
• Default: compiler.context

The context used to create relative module identifiers before ids are generated.

#test

• Type: (module: Module) => boolean
• Default: undefined

Selects which modules should receive deterministic ids from this plugin. When omitted, all modules that need ids are included.

import rspack from '@rspack/core';

export default {
  optimization: {
    moduleIds: false,
  },
  plugins: [
    new rspack.ids.DeterministicModuleIdsPlugin({
      test: (module) => module.type.startsWith('css'),
    }),
  ],
};

#maxLength

• Type: number
• Default: 3

The maximum id length in digits used as the starting id space. The generated numeric id space starts at 10 ** maxLength.

#salt

• Type: number
• Default: 0

The hash salt used when generating ids. Change this value to try a different hash starting value in the same id space.

#fixedLength

• Type: boolean
• Default: false

When enabled, Rspack does not increase the id length to find a larger id space.

#failOnConflict

• Type: boolean
• Default: false

When enabled, Rspack reports an error if deterministic id assignment produces conflicts. By default, Rspack resolves conflicts by retrying with a larger id space.

#Usage with optimization.moduleIds

For the common long-term caching setup, prefer the built-in optimization option:

export default {
  optimization: {
    moduleIds: 'deterministic',
  },
};

Use DeterministicModuleIdsPlugin directly only when you need the options above.