# @tybys/wasm-util

> WASI polyfill for browser and some wasm util

Latest version **0.10.3** (published 2026-06-23) · MIT license · 0 weekly downloads

## Install

```sh
npm install @tybys/wasm-util
pnpm add @tybys/wasm-util
yarn add @tybys/wasm-util
bun add @tybys/wasm-util
```

## Health

**Score 55/100 (C)** — status: active.

Positive: no vulnerabilities; recently updated; high maintenance score.

Warnings: low downloads; no types; no esm support; pre 1.0.

## Facts

| | |
|---|---|
| Version | 0.10.3 |
| Published | 2026-06-23 |
| First published | 2022-10-28 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | none |
| Module format | CommonJS |
| Dependencies | 0 |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 40 |
| Author | toyobayashi |
| Maintainers | toyobayashi |
| Keywords | wasm, webassembly, wasi, polyfill |

## Links

- npm: https://www.npmjs.com/package/@tybys/wasm-util
- Repository: https://github.com/toyobayashi/wasm-util
- Homepage: https://github.com/toyobayashi/wasm-util#readme
- Issues: https://github.com/toyobayashi/wasm-util/issues
- npm.io page: https://npm.io/package/@tybys/wasm-util

## Recent versions

- 0.10.3 (latest) — 2026-06-23
- 0.10.2 — 2026-05-04
- 0.10.1 — 2025-09-11
- 0.10.0 — 2025-07-08
- 0.9.0 — 2024-05-07
- 0.8.3 — 2024-04-21
- 0.8.2 — 2024-04-19
- 0.8.1 — 2024-01-07
- 0.8.0 — 2023-02-26
- 0.7.0 — 2023-02-19
- 0.6.0 — 2023-02-19
- 0.5.3 — 2022-12-11
- 0.5.2 — 2022-12-11
- 0.5.1 — 2022-12-11
- 0.5.0 — 2022-12-11
- … 4 more at https://npm.io/package/@tybys/wasm-util/versions

## README

# @tybys/wasm-util

WebAssembly related utils for browser environment

**The output code is ES2019**

## Features

All example code below need to be bundled by ES module bundlers like `webpack` / `rollup`, or specify import map in browser native ES module runtime.

### WASI polyfill for browser

The API is similar to the `require('wasi').WASI` in Node.js.

You can use `memfs-browser` to provide filesystem capability.

- Example: [https://github.com/toyobayashi/wasi-wabt](https://github.com/toyobayashi/wasi-wabt)
- Demo: [https://toyobayashi.github.io/wasi-wabt/](https://toyobayashi.github.io/wasi-wabt/)

```js
import { load, WASI } from '@tybys/wasm-util'
import { Volume, createFsFromVolume } from 'memfs-browser'

const fs = createFsFromVolume(Volume.fromJSON({
  '/home/wasi': null
}))

const wasi = new WASI({
  args: ['chrome', 'file.wasm'],
  env: {
    NODE_ENV: 'development',
    WASI_SDK_PATH: '/opt/wasi-sdk'
  },
  preopens: {
    '/': '/'
  },
  fs,

  // redirect stdout / stderr

  // print (text) { console.log(text) },
  // printErr (text) { console.error(text) }
})

const imports = {
  wasi_snapshot_preview1: wasi.wasiImport
}

const { module, instance } = await load('/path/to/file.wasm', imports)
wasi.start(instance)
// wasi.initialize(instance)
```

Implemented syscalls: [wasi_snapshot_preview1](#wasi_snapshot_preview1)

### `load` / `loadSync`

`loadSync` has 4KB wasm size limit in browser.

```js
// bundler
import { load, loadSync } from '@tybys/wasm-util'

const imports = { /* ... */ }

// using path
const { module, instance } = await load('/path/to/file.wasm', imports)
const { module, instance } = loadSync('/path/to/file.wasm', imports)

// using URL
const { module, instance } = await load(new URL('./file.wasm', import.meta.url), imports)
const { module, instance } = loadSync(new URL('./file.wasm', import.meta.url), imports)

// using Uint8Array
const buffer = new Uint8Array([
  0x00, 0x61, 0x73, 0x6d,
  0x01, 0x00, 0x00, 0x00
])
const { module, instance } = await load(buffer, imports)
const { module, instance } = loadSync(buffer, imports)

// auto asyncify
const {
  module,
  instance: asyncifiedInstance
} = await load(buffer, imports, { /* asyncify options */})
asyncifiedInstance.exports.fn() // => return Promise
```

### Extend Memory instance

```js
import { Memory, extendMemory } from '@tybys/wasm-util'

const memory = new WebAssembly.Memory({ initial: 256 })
// const memory = instance.exports.memory

extendMemory(memory)
console.log(memory instanceof Memory)
console.log(memory instanceof WebAssembly.Memory)
// expose memory view getters like Emscripten
const { HEAPU8, HEAPU32, view } = memory
```

### Asyncify wrap

Build the C code using `clang`, `wasm-ld` and `wasm-opt`

```c
void async_sleep(int ms);

int main() {
  async_sleep(200);
  return 0;
}
```

```js
import { Asyncify } from '@tybys/wasm-util'

const asyncify = new Asyncify()

const imports = {
  env: {
    async_sleep: asyncify.wrapImportFunction(function (ms) {
      return new Promise((resolve) => {
        setTimeout(resolve, ms)
      })
    })
  }
}

// async_sleep(200)
const bytes = await (await fetch('/asyncfied_by_wasm-opt.wasm')).arrayBuffer()
const { instance } = await WebAssembly.instantiate(bytes, imports)
const asyncifiedInstance = asyncify.init(instance.exports.memory, instance, {
  wrapExports: ['_start']
})

const p = asyncifedInstance._start()
console.log(typeof p.then === 'function')
const now = Date.now()
await p
console.log(Date.now() - now >= 200)
```

### wasi_snapshot_preview1

- [x] args_get
- [x] args_sizes_get
- [x] environ_get
- [x] environ_sizes_get
- [x] clock_res_get
- [x] clock_time_get
- [ ] ~~fd_advise~~
- [x] fd_allocate
- [x] fd_close
- [x] fd_datasync
- [x] fd_fdstat_get
- [ ] ~~fd_fdstat_set_flags~~
- [x] fd_fdstat_set_rights
- [x] fd_filestat_get
- [x] fd_filestat_set_size
- [x] fd_filestat_set_times
- [x] fd_pread
- [x] fd_prestat_get
- [x] fd_prestat_dir_name
- [x] fd_pwrite
- [x] fd_read
- [x] fd_readdir
- [x] fd_renumber
- [x] fd_seek
- [x] fd_sync
- [x] fd_tell
- [x] fd_write
- [x] path_create_directory
- [x] path_filestat_get
- [x] path_filestat_set_times
- [x] path_link
- [x] path_open
- [x] path_readlink
- [x] path_remove_directory
- [x] path_rename
- [x] path_symlink
- [x] path_unlink_file
- [x] poll_oneoff (timer only)
- [x] proc_exit
- [ ] ~~proc_raise~~
- [x] sched_yield
- [x] random_get
- [ ] ~~sock_recv~~
- [ ] ~~sock_send~~
- [ ] ~~sock_shutdown~~

---
_Source: https://npm.io/package/@tybys/wasm-util · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._