# Getting Started

@napi-rs/wasm-tools is walrus behind a small JavaScript API: read, edit, and build WebAssembly modules from Node.js. It loads a prebuilt native binary — no compiler, no node-gyp.

# Install

pnpm add @napi-rs/wasm-tools -D

yarn add @napi-rs/wasm-tools -D

Version note. Most of this page requires @napi-rs/wasm-tools ≥ 1.0.2 — the module graph (mod.functions, mod.exports, live handles), buildFunction, instructions(), WasmModule.fromBuffer, emitWasmFile, and the I32 … V128 value constants all arrive in 1.0.2, which is not published yet. The current npm release (1.0.1) exposes only ModuleConfig (the chainable builder plus parse) and WasmModule.fromPath / fromFileWithConfig / emitWasm — the Parse with options, then emit example below works on 1.0.1 today. To try the ≥ 1.0.2 APIs now, use the playground on this site, which runs a vendored pre-release build.

# Get a module

Parse wasm into a live WasmModule:

• WasmModule.fromBuffer(bytes) (≥ 1.0.2) — parse in-memory bytes with the defaults.
• WasmModule.fromPath(path) / fromFileWithConfig(path, config) — parse a file (available in 1.0.1).
• new ModuleConfig().….parse(bytes) — parse in-memory bytes with walrus options (DWARF, name section, …; available in 1.0.1).

// Reading mod.functions / mod.exports requires @napi-rs/wasm-tools >= 1.0.2.
import { readFile } from 'node:fs/promises'
import { WasmModule } from '@napi-rs/wasm-tools'

const mod = WasmModule.fromBuffer(await readFile('./module.wasm'))
console.log(mod.functions.length, mod.exports.length)

# Parse with options, then emit

ModuleConfig is a chainable builder; parse() returns the module and emitWasm(demangle) serializes it back to bytes.

import { ModuleConfig } from '@napi-rs/wasm-tools'

const binary = new ModuleConfig()
  .generateDwarf(true)
  .generateNameSection(true)
  .generateProducersSection(true)
  .preserveCodeTransform(true)
  .parse(wasm)
  .emitWasm(true)

emitWasm(true) demangles Rust/C++ symbol names in the output; pass false to keep them raw. There is also emitWasmFile(path, demangle) to write straight to disk.

# Where to next

• The module graph — the collections and live handles you read and edit through.
• Value types & constants — the ready-made I32 … V128 and reference-type constants.
• Building functions — synthesize function bodies from instruction descriptors.
• API reference — every class and constant.