agent-skills/skills/tsdown/references/option-sourcemap.md

Source Maps

Generate source maps for debugging bundled code.

Overview

Source maps map minified/bundled code back to original source files, making debugging significantly easier by showing original line numbers and variable names.

Basic Usage

CLI

tsdown --sourcemap

# Or inline
tsdown --sourcemap inline

Config File

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

Source Map Types

External (default)

Generates separate .map files:

export default defineConfig({
  sourcemap: true,  // or 'external'
})

Output:

• dist/index.mjs
• dist/index.mjs.map

Pros:

• Smaller bundle size
• Can be excluded from production
• Faster parsing

Inline

Embeds source maps in the bundle:

export default defineConfig({
  sourcemap: 'inline',
})

Output:

• dist/index.mjs (includes source map as data URL)

Pros:

• Single file deployment
• Guaranteed to be available

Cons:

• Larger bundle size
• Exposed in production

Hidden

Generates map files without reference comment:

export default defineConfig({
  sourcemap: 'hidden',
})

Output:

• dist/index.mjs (no //# sourceMappingURL comment)
• dist/index.mjs.map

Use when:

• You want maps for error reporting tools
• But don't want them exposed to users

Auto-Enable Scenarios

Declaration Maps

If declarationMap is enabled in tsconfig.json, source maps are automatically enabled:

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

This also generates .d.ts.map files for TypeScript declarations.

Common Patterns

Development Build

export default defineConfig((options) => ({
  entry: ['src/index.ts'],
  sourcemap: options.watch,  // Only in dev
  minify: !options.watch,
}))

Production with External Maps

export default defineConfig({
  entry: ['src/index.ts'],
  format: ['esm', 'cjs'],
  sourcemap: true,  // External maps
  minify: true,
})

Deploy maps to separate error reporting service.

Always Inline (Development Tool)

export default defineConfig({
  entry: ['src/index.ts'],
  format: ['esm'],
  sourcemap: 'inline',
})

Per-Format Source Maps

export default defineConfig({
  entry: ['src/index.ts'],
  format: {
    esm: {
      sourcemap: true,
    },
    iife: {
      sourcemap: 'inline',  // Inline for browser
    },
  },
})

TypeScript Library with Declaration Maps

export default defineConfig({
  entry: ['src/index.ts'],
  format: ['esm', 'cjs'],
  sourcemap: true,
  dts: {
    sourcemap: true,  // Enable declaration maps
  },
})

Output:

• dist/index.mjs + dist/index.mjs.map
• dist/index.cjs + dist/index.cjs.map
• dist/index.d.ts + dist/index.d.ts.map

Benefits

For Development

• Faster debugging - See original code in debugger
• Better error messages - Stack traces show original lines
• Easier breakpoints - Set breakpoints on source code

For Production

• Error reporting - Send accurate error locations to services
• Monitoring - Track errors back to source
• Support - Help users report issues accurately

Performance Impact

Type	Bundle Size	Parse Speed	Debugging
None	Smallest	Fastest	Hard
External	Small	Fast	Easy
Inline	Largest	Slower	Easy
Hidden	Small	Fast	Tools only

CLI Examples

# Enable source maps
tsdown --sourcemap

# Inline source maps
tsdown --sourcemap inline

# Hidden source maps
tsdown --sourcemap hidden

# Development with source maps
tsdown --watch --sourcemap

# Production with external maps
tsdown --minify --sourcemap

# No source maps
tsdown --no-sourcemap

Use Cases

Local Development

export default defineConfig({
  sourcemap: true,
  minify: false,
})

Production Build

export default defineConfig({
  sourcemap: 'external',  // Upload to error service
  minify: true,
})

Browser Library

export default defineConfig({
  format: ['iife'],
  platform: 'browser',
  sourcemap: 'inline',  // Self-contained
  globalName: 'MyLib',
})

Node.js CLI Tool

export default defineConfig({
  format: ['esm'],
  platform: 'node',
  sourcemap: true,
  shims: true,
})

Troubleshooting

Source Maps Not Working

1. Check output - Verify .map files are generated
2. Check reference - Look for //# sourceMappingURL= comment
3. Check paths - Ensure relative paths are correct
4. Check tool - Verify debugger/browser supports source maps

Large Bundle Size

Use external source maps instead of inline:

export default defineConfig({
  sourcemap: true,  // Not 'inline'
})

Source Not Found

• Ensure source files are accessible relative to map
• Check sourceRoot in generated map
• Verify paths in sources array

Tips

1. Use external maps for production (smaller bundles)
2. Use inline maps for single-file tools
3. Enable in development for better DX
4. Upload to error services for production debugging
5. Use hidden maps when you want them for tools only
6. Enable declaration maps for TypeScript libraries

Related Options

• Minification - Code compression
• DTS - TypeScript declarations
• Watch Mode - Development workflow
• Target - Syntax transformations