/tsdown

Output Options

Format

Default: esm

defineConfig({
  format: 'esm',                 // ECMAScript Modules
  format: 'cjs',                 // CommonJS
  format: 'iife',                // Browser script
  format: 'umd',                 // Universal
  format: ['esm', 'cjs'],        // Multiple
})

Format-specific config:

defineConfig({
  format: {
    esm: { target: ['es2015'] },
    cjs: { target: ['node20'] },
  },
})

Output Directory

defineConfig({
  outDir: 'dist',  // Default
})

tsdown -d ./build
tsdown --out-dir ./build

Target

Syntax downleveling (no polyfills):

defineConfig({
  target: 'es2020',
  target: 'node20',
  target: ['chrome100', 'firefox90'],
})

Default: reads from engines.node in package.json.

Disable transformations:

defineConfig({
  target: false,  // Preserve modern syntax
})

Platform

defineConfig({
  platform: 'node',     // Default, Node.js built-ins external
  platform: 'browser',  // Web browsers
  platform: 'neutral',  // Platform-agnostic
})

Module resolution:

• node: mainFields: ['main', 'module']
• browser: mainFields: ['browser', 'module', 'main']
• neutral: relies on exports field only

Declaration Files (.d.ts)

defineConfig({
  dts: true,  // Enable
})

Auto-enabled if types or typings in package.json.

Performance with isolatedDeclarations

For fastest .d.ts generation:

// tsconfig.json
{
  "compilerOptions": {
    "isolatedDeclarations": true
  }
}

Uses oxc-transform instead of slower TypeScript.

Declaration Maps

defineConfig({
  dts: {
    sourcemap: true,  // .d.ts.map files
  },
})

Or via tsconfig.json:

{
  "compilerOptions": {
    "declarationMap": true
  }
}

Vue Support

defineConfig({
  dts: { vue: true },  // Requires vue-tsc
})

Dependencies

Default Behavior

Skip All node_modules

defineConfig({
  skipNodeModulesBundle: true,
})

Custom External

defineConfig({
  external: ['lodash', /^@my-scope\//],
})

Force Bundle

defineConfig({
  noExternal: ['some-package'],  // Bundle despite being in deps
})

Package Exports

Auto-generate exports, main, module, types:

defineConfig({
  exports: true,
})

Export All Files

defineConfig({
  exports: {
    all: true,  // Not just entry files
  },
})

Dev Exports

Point to source during development:

defineConfig({
  exports: {
    devExports: true,
  },
})

exports → source, publishConfig.exports → built.

CSS Exports

defineConfig({
  css: {
    splitting: false,
    fileName: 'my-library.css',
  },
  exports: true,
})

Custom Exports

defineConfig({
  exports: {
    customExports(pkg, context) {
      pkg['./foo'] = './foo.js'
      return pkg
    },
  },
})

Cleaning

Output directory cleaned by default:

defineConfig({
  clean: true,   // Default
  clean: false,  // Keep existing
})

Example package.json

{
  "name": "my-lib",
  "type": "module",
  "main": "./dist/index.cjs",
  "module": "./dist/index.js",
  "types": "./dist/index.d.ts",
  "exports": {
    ".": {
      "import": {
        "types": "./dist/index.d.ts",
        "default": "./dist/index.js"
      },
      "require": {
        "types": "./dist/index.d.cts",
        "default": "./dist/index.cjs"
      }
    }
  },
  "files": ["dist"]
}