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A high-level AssemblyScript layer for the WebAssembly System Interface (WASI). 🧩

WASI is an API providing access to the external world to WebAssembly modules. AssemblyScript exposes the low-level WASI standard set of system calls. as-wasi builds a higher level API on top of the AssemblyScript WASI interface, at a similar level to the Node API. 🚀


You can install as-wasi in your project by running the following:

npm install --save as-wasi

Quick Start

Example usage of the Console and Environ classes:

// Import from the installed as-wasi package
import { Console, Environ } from "as-wasi/assembly";

// Create an environ instance
let env = new Environ();

// Get the HOME Environment variable
let home = env.get("HOME")!;

// Log the HOME string to stdout

Here are some exported classes that are commonly used:

  • FileSystem - Reading and Writing the user's fileystem. 📁
  • Console - General logging to stdout and stderr. 🖥️
  • Environ - Accessing environment variables, command flags, etc... 🌐
  • Date - Getting the current system time. 📅
  • Random - Accessing random numbers. 🤔
  • Time - Allow sleeping and waiting for events to occur.
  • And More! See the Reference API in the next section for the full API.

Reference API Docs

Reference API documentation can be found in REFERENCE_API_DOCS. Documentation is generated using typedoc.

Projects using as-wasi

  • wasmboy - Game Boy / Game Boy Color Emulator Library, 🎮written for WebAssembly using AssemblyScript. 🚀
  • wasmerio/io-devices-lib - Library for interacting with the Wasmer Experimental IO Devices API. Uses WASI for outputting graphics in a framebuffer, and handles mouse/keyboard input.
  • wasm-by-example - Wasm By Example is a website with a set of hands-on introduction examples and tutorials for WebAssembly (Wasm). Wasm By Example features as-wasi by default for the AssemblyScript WASI examples.
  • wasm-matrix - A Matrix effect in your terminal using AssemblyScript 🚀 and WASI 🧩 . This project is a bit older, and uses an older version of as-wasi, but still creates a cool effect!

If your project is using as-wasi, and you would like to be featured here. Please open a pull request against the README with links to your project, and if appropriate, explaining how as-wasi is being used. 😊


Contributions are definitely welcome! Feel free to open a PR for small fixes such as typos and things. Larger fixes, or new features should start out as an issue for discussion, in which then a PR should be made. 🥳

This project will also adhere to the AssemblyScript Code of Conduct.


MIT. 📝




npm i as-wasi

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  • jedisct1