WASM Support

tsdown supports bundling WebAssembly (WASM) modules through rolldown-plugin-wasm. This plugin allows you to import .wasm files directly in your TypeScript or JavaScript code, with support for both synchronous and asynchronous instantiation.

Minimal Example

To configure tsdown for WASM support, add the plugin to your tsdown.config.ts:

tsdown.config.ts

import { wasm } from 'rolldown-plugin-wasm'
import { defineConfig } from 'tsdown'

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

Install the required dependency:

npm

npm install -D rolldown-plugin-wasm

pnpm

pnpm add -D rolldown-plugin-wasm

yarn

yarn add -D rolldown-plugin-wasm

bun

bun add -D rolldown-plugin-wasm

Importing WASM Modules

You can import WASM modules directly:

import { add } from './add.wasm'

add(1, 2)

Asynchronous Init

Use the ?init query to get an async initialization function:

import init from './add.wasm?init'

const instance = await init(
  imports, // optional
)

instance.exports.add(1, 2)

Synchronous Init

Use the ?init&sync query for synchronous initialization:

import initSync from './add.wasm?init&sync'

const instance = initSync(
  imports, // optional
)

instance.exports.add(1, 2)

wasm-bindgen Support

Target bundler (Default, Recommended)

import { add } from 'some-pkg'

add(1, 2)

Target web

Node.js

import { readFile } from 'node:fs/promises'
import init, { add } from 'some-pkg'
import wasmUrl from 'some-pkg/add_bg.wasm?url'

await init({
  module_or_path: readFile(new URL(wasmUrl, import.meta.url)),
})

add(1, 2)

Browser

import init, { add } from 'some-pkg/add.js'
import wasmUrl from 'some-pkg/add_bg.wasm?url'

await init({
  module_or_path: wasmUrl,
})

add(1, 2)

NOTE

Other wasm-bindgen targets such as nodejs and no-modules are not supported.

TypeScript Support

To get type support for .wasm imports, add the type declarations to your tsconfig.json:

tsconfig.json

{
  "compilerOptions": {
    "types": ["rolldown-plugin-wasm/types"],
  },
}

Options

The plugin accepts an options object:

wasm({
  maxFileSize: 14 * 1024, // Max file size for inline (default: 14KB)
  fileName: '[hash][extname]', // Output file name pattern
  publicPath: '', // Prefix for non-inlined file paths
  targetEnv: 'auto', // 'auto' | 'auto-inline' | 'browser' | 'node'
})

Option	Default	Description
maxFileSize	14 * 1024	Maximum file size for inlining. Files exceeding this limit are copied to the output directory and loaded at runtime. Set to 0 to always copy.
fileName	'[hash][extname]'	Pattern for renaming emitted WASM files.
publicPath	—	Prefix added to file paths for non-inlined WASM files.
targetEnv	'auto'	Controls the generated instantiation code. 'auto' detects the environment at runtime; 'auto-inline' always inlines and decodes based on environment; 'browser' omits Node.js builtins; 'node' omits fetch (requires Node.js 20.16.0+).