#source.define

• Type: Record<string, unknown>
• Default: {}

Replaces variables in your code with other values or expressions at compile time. This is useful for enabling different behavior between development and production builds.

Each key passed into the configuration is an identifier or multiple identifiers joined with ..

• If the value is a string, it will be used as a code fragment.
• If the value is not a string, it will be stringified (including functions).
• If the value is an object, all keys are defined the same way.
• If you prefix typeof to the key, it is only defined for typeof calls.

For more usage, please refer to Using define and Rspack - DefinePlugin.

#Example

export default {
  source: {
    define: {
      PRODUCTION: JSON.stringify(true),
      VERSION: JSON.stringify('5fa3b9'),
      BROWSER_SUPPORTS_HTML5: true,
      TWO: '1 + 1',
      'typeof window': JSON.stringify('object'),
      'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
      'import.meta.test': JSON.stringify('foo'),
    },
  },
};

Expressions will be replaced with the corresponding code fragments:

const foo = TWO;

// ⬇️ Turns into
const foo = 1 + 1;