Root Directory

The root option specifies the root directory of your input files, similar to TypeScript's rootDir. It determines how the output directory structure is computed from your entry files.

Default Behavior

By default, root is automatically computed as the common base directory of all entry files. For example, if your entries are src/a.ts and src/b.ts, the root will be src/.

How to Configure

import { defineConfig } from 'tsdown'

export default defineConfig({
  entry: ['src/index.ts', 'src/utils/helper.ts'],
  root: 'src',
})

Or via CLI:

tsdown --root src

How It Works

The root option affects two behaviors:

1. Entry name resolution: When using array entries, file paths relative to root determine the output filenames.
2. Unbundle mode: In unbundle mode, root is used as the preserveModulesRoot, controlling the output directory structure.

Example

Given the following project structure:

project/
  src/
    index.ts
    utils/
      helper.ts

Without root (default behavior)

export default defineConfig({
  entry: ['src/index.ts', 'src/utils/helper.ts'],
})

The common base directory is src/, so the output will be:

dist/
  index.js
  utils/
    helper.js

With explicit root

export default defineConfig({
  entry: ['src/index.ts', 'src/utils/helper.ts'],
  root: '.',
})

Now the root is the project directory, so the output preserves the src/ prefix:

dist/
  src/
    index.js
    utils/
      helper.js

When to Use

• When the auto-computed common base directory doesn't produce the desired output structure.
• When you want output paths to include or exclude certain directory prefixes.
• When using unbundle mode and need fine-grained control over the output directory mapping.