cranelift/docs/wasm-assemblyscript.md

AssemblyScript

[AssemblyScript] has included support for targeting WASI since version 0.10.0. If you're not familiar with AssemblyScript, check out the docs or the discord server. To setup this demo, you need a valid installation of NodeJS, Deno, or Bun along with a installation of wasmtime.

For the rest of this documentation, we'll default to NPM as our package manager. Feel free to use the manager of your choice.

Let's walk through a simple hello world example using the latest AssemblyScript runtime (at the time of this writing, it is AssemblyScript runtime included in version 0.27.x):

Hello World!

Enabling WASI support in AssemblyScript requires some configuration and dependencies in order to compile with WASI support.

First, we'll install assemblyscript along with wasi-shim which is a plugin that adds support for WASI.

$ npm install --save-dev assemblyscript @assemblyscript/wasi-shim

Next, we'll use the built in asinit command to create our project files. When prompted, type y and return.

$ npx asinit .

Next, we need to configure our project to use WASI as a build target. Navigate to asconfig.json and add the following line.

asconfig.json

{
    // "targets": { ... },
    "extends": "./node_modules/@assemblyscript/wasi-shim/asconfig.json"
}

With AssemblyScript now configured to use WASI, we can enter ./assembly/index.ts and change it to the following. This will tell WASI to print the string to the terminal.

assembly/index.ts

console.log("Hello World!");

Now, compile our WASI module using the asc command and run it using wasmtime.

$ npx asc assembly/index.ts --target release
$ wasmtime ./build/release.wasm

Now that we know how to use WASI, we'll test the capabilities of WASI using a demo.

WASI Demo

First, clone the wasmtime repository and navigate to the docs/assemblyscript_demo directory.

$ git clone https://github.com/bytecodealliance/wasmtime
$ cd wasmtime/docs/assemblyscript_demo

Install our dependencies with NPM or your preferred package manager.

$ npm install

Take a look at the code in docs/assemblyscript_demo/wasi-demo.ts and then build the WASM/WASI binary by running

$ npx asc wasi-demo.ts --target wasi-demo

Lastly, run the demo using

$ wasmtime ./build/wasi-demo.wasm