README.md

1. Download javy from https://github.com/Shopify/javy/releases/latest
2. ./javy compile fib.js -o fib.wasm
3. node server.js

Note: In order to support node modules, you need to use a bundler to include every module in 1 file and then compile to wasm. ref: bytecodealliance/javy#265

More info: https://nodejs.org/api/wasi.html

fib.js

function fib(n) {
  var a = 0, b = 1
  if (n > 0) {
    while (--n) {
      let t = a + b
      a = b
      b = t
    }
    return b
  }
  return a
}

console.log(fib(20));

package.json

{
  "type": "module",
  "name": "wasm",
  "version": "1.0.0",
  "description": "",
  "main": "server.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "node server.js"
  },
  "author": "",
  "license": "ISC"
}

server.js

import { readFile } from 'node:fs/promises';
import { WASI } from 'wasi';
import { argv, env } from 'node:process';

const wasi = new WASI({
  version: 'preview1',
  args: argv,
  env,
  /*
  We don't ned fileystem access, but if we did this is how it would work:
  preopens: {
    '/sandbox': '/tmp',
  },
  */
});

const wasm = await WebAssembly.compile(
  await readFile(new URL('./fib.wasm', import.meta.url)),
);

const instance = await WebAssembly.instantiate(wasm, wasi.getImportObject());

wasi.start(instance);