transform

• Type: object with the properties below
• Optional

Defined in: packages/rolldown/src/options/input-options.ts:737

Configure how the code is transformed. This process happens after the transform hook.

Example

Enable legacy decorators

export default defineConfig({
  transform: {
    decorator: {
      legacy: true,
    },
  },
})

Note that if you have correct tsconfig.json file, Rolldown will automatically detect and enable legacy decorators support.

In-depth

Rolldown uses Oxc under the hood for transformation.

While Oxc does not support lowering the latest decorators proposal yet, Rolldown is able to bundle them.

assumptions?

• Type: CompilerAssumptions
• Optional

Defined in: packages/rolldown/src/binding.d.cts:1273

Set assumptions in order to produce smaller output.

Inherited from

Omit.assumptions

decorator?

• Type: DecoratorOptions
• Optional

Defined in: packages/rolldown/src/binding.d.cts:1312

Decorator plugin

Inherited from

Omit.decorator

define?

• Type: Record<string, string>
• Optional

Defined in: packages/rolldown/src/options/transform-options.ts:51

Replace global variables or property accessors with the provided values.

See Oxc's define option for more details.

Example

Replace the global variable IS_PROD with true

rolldown.config.js

export default defineConfig({
  transform: { define: { IS_PROD: 'true' } }
})

Result:

// Input
if (IS_PROD) {
  console.log('Production mode')
}

// After bundling
if (true) {
  console.log('Production mode')
}

Replace the property accessor process.env.NODE_ENV with 'production'

rolldown.config.js

export default defineConfig({
  transform: { define: { 'process.env.NODE_ENV': "'production'" } }
})

Result:

// Input
if (process.env.NODE_ENV === 'production') {
  console.log('Production mode')
}

// After bundling
if ('production' === 'production') {
  console.log('Production mode')
}

dropLabels?

• Type: string[]
• Optional

Defined in: packages/rolldown/src/options/transform-options.ts:106

Remove labeled statements with these label names.

Labeled statements are JavaScript statements prefixed with a label identifier. This option allows you to strip specific labeled statements from the output, which is useful for removing debug-only code in production builds.

Example

export default defineConfig({
  transform: { dropLabels: ['DEBUG', 'DEV'] }
})

Result:

// Input
DEBUG: console.log('Debug info');
DEV: {
  console.log('Development mode');
}
console.log('Production code');

// After bundling
console.log('Production code');

helpers?

• Type: Helpers
• Optional

Defined in: packages/rolldown/src/binding.d.cts:1300

Behaviour for runtime helpers.

Inherited from

Omit.helpers

inject?

• Type: Record<string, string | [string, string]>
• Optional

Defined in: packages/rolldown/src/options/transform-options.ts:79

Inject import statements on demand.

The API is aligned with @rollup/plugin-inject.

See Oxc's inject option for more details.

Supported patterns

{
  // import { Promise } from 'es6-promise'
  Promise: ['es6-promise', 'Promise'],

  // import { Promise as P } from 'es6-promise'
  P: ['es6-promise', 'Promise'],

  // import $ from 'jquery'
  $: 'jquery',

  // import * as fs from 'node:fs'
  fs: ['node:fs', '*'],

  // Inject shims for property access pattern
  'Object.assign': path.resolve( 'src/helpers/object-assign.js' ),
}

jsx?

• Type: false | "react" | "react-jsx" | "preserve" | JsxOptions
• Optional

Defined in: packages/rolldown/src/options/transform-options.ts:115

Controls how JSX syntax is transformed.

• If set to false, an error will be thrown if JSX syntax is encountered.
• If set to 'react', JSX syntax will be transformed to classic runtime React code.
• If set to 'react-jsx', JSX syntax will be transformed to automatic runtime React code.
• If set to 'preserve', JSX syntax will be preserved as-is.

plugins?

• Type: PluginsOptions
• Optional

Defined in: packages/rolldown/src/binding.d.cts:1317

Third-party plugins to use.

See

https://oxc.rs/docs/guide/usage/transformer/plugins

Inherited from

Omit.plugins

target?

• Type: string | string[]
• Optional

Defined in: packages/rolldown/src/binding.d.cts:1298

Sets the target environment for the generated JavaScript.

The lowest target is es2015.

Example:

• 'es2015'
• ['es2020', 'chrome58', 'edge16', 'firefox57', 'node12', 'safari11']

Default

esnext (No transformation)

See

https://oxc.rs/docs/guide/usage/transformer/lowering#target

Inherited from

Omit.target

typescript?

• Type: TypeScriptOptions
• Optional

Defined in: packages/rolldown/src/binding.d.cts:1278

Configure how TypeScript is transformed.

See

https://oxc.rs/docs/guide/usage/transformer/typescript

Inherited from

Omit.typescript