Output Format

By default, tsdown generates JavaScript code in the ESM (ECMAScript Module) format. However, you can specify the desired output format using the --format option:

tsdown --format esm # default

Available Formats

• esm: ECMAScript Module format, ideal for modern JavaScript environments, including browsers and Node.js.
• cjs: CommonJS format, commonly used in Node.js projects.
• iife: Immediately Invoked Function Expression, suitable for embedding in <script> tags or standalone browser usage.
• umd: Universal Module Definition, a format that works on AMD, CommonJS, and global variables.

Example

# Generate ESM output (default)
tsdown --format esm

# Generate both ESM and CJS outputs
tsdown --format esm --format cjs

# Generate IIFE output for browser usage
tsdown --format iife

TIP

You can specify multiple formats in a single command to generate outputs for different environments. For example, combining esm and cjs ensures compatibility with both modern and legacy systems.

Overriding Configuration by Format

You can override specific configuration options for each output format by setting format as an object in your config file. This allows you to tailor settings such as target or other options for each format individually.

export default defineConfig({
  entry: ['./src/index.js'],
  format: {
    esm: {
      target: ['es2015'],
    },
    cjs: {
      target: ['node20'],
    },
  },
})

In this example, the ESM output will target ES2015, while the CJS output will target Node.js 20. This approach gives you fine-grained control over the build process for different module formats.