Option Tree Shaking

# Tree shaking enabled (default)
tsdown

# Disable tree shaking
tsdown --no-treeshake

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

// src/util.ts
export function unused() {
  console.log("I'm unused")
}

export function hello(x: number) {
  console.log('Hello World', x)
}

// src/index.ts
import { hello } from './util'
hello(1)

// dist/index.mjs
function hello(x) {
  console.log('Hello World', x)
}
hello(1)

// dist/index.mjs
function unused() {
  console.log("I'm unused")
}

function hello(x) {
  console.log('Hello World', x)
}
hello(1)

export default defineConfig({
  treeshake: true,
})

export default defineConfig({
  treeshake: {
    moduleSideEffects: false,
    propertyReadSideEffects: false,
    unknownGlobalSideEffects: false,
  },
})

export default defineConfig({
  treeshake: false,
})

{
  "sideEffects": false
}

{
  "sideEffects": ["*.css", "src/polyfills.ts"]
}

export default defineConfig({
  treeshake: {
    moduleSideEffects: (id) => {
      // Preserve side effects for polyfills
      return id.includes('polyfill')
    },
  },
})

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

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

export default defineConfig({
  entry: ['src/index.ts'],
  treeshake: {
    moduleSideEffects: (id) => {
      return (
        id.includes('.css') ||
        id.includes('polyfill') ||
        id.includes('side-effect')
      )
    },
  },
})

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

import { onlyWhatINeed } from 'my-utils'

export default defineConfig((options) => ({
  treeshake: !options.watch,
}))

// This has side effects
window.myGlobal = {}

export function setup() {
  // ...
}

{
  "sideEffects": true
}

export default defineConfig({
  treeshake: false,
})

// utils.ts - perfect for tree shaking
export function add(a, b) {
  return a + b
}

export function multiply(a, b) {
  return a * b
}

// Only 'add' imported = only 'add' bundled
import { add } from './utils'

// polyfill.ts - has side effects
if (!Array.prototype.at) {
  Array.prototype.at = function(index) {
    // polyfill implementation
  }
}

export {} // Need to export something

{
  "sideEffects": ["src/polyfill.ts"]
}