Typescript - Assembly Script

typescript/assembly

A TypeScript-like language for WebAssembly

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Introduction

AssemblyScript compiles a variant of TypeScript (a typed superset of JavaScript) to WebAssembly using Binaryen.

Good use cases for AssemblyScript are computation-heavy logic like image manipulation, hot game logic, specialized algorithms, emulators, compilers, and the likes.

Project

Create a new project with Deno

Terminal window
deno init assembly
Terminal window
npm init -y
npm install --save-dev assemblyscript
npx asinit .

This creates assembly/ with index.ts and asconfig.json, plus build scripts in package.json.

Build the WebAssembly module

Terminal window
npm run asbuild      # or: npx asc assembly/index.ts --target release

Output will be in build/ (e.g., build/release.wasm).

Import and run the WASM in Deno

Create main.ts:

const wasmUrl = new URL("./build/release.wasm", import.meta.url);
const wasmModule = await WebAssembly.instantiate(
  await Deno.readFile(wasmUrl),
  {}, // import object if needed
);
const { add } = wasmModule.instance.exports as { add(a: number, b: number): number };
console.log(add(2, 3)); // expect 5

Run:

Terminal window
deno run --allow-read main.ts

Develop your AssemblyScript code

  • Edit assembly/index.ts. Export functions you need in JS/TS:
export function add(a: i32, b: i32): i32 {
    return a + b;
}

Rebuild after changes: npm run asbuild.

Optional Deno config

If you want TypeScript pathing or permissions presets, create deno.json:

{
  "tasks": {
    "start": "deno run --allow-read main.ts"
  }
}

Then run: deno task start.

Debugging tips

  • Use npm run asbuild:debug (generated by asinit) for better stack traces.
  • Check asconfig.json targets to tweak optimization levels or exports.

That’s it—modify assembly/index.ts, rebuild, and run via Deno.

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