bun.sh/src/js/wasi-runner.js

/** This file is used when a .wasm file is ran.
 *  The transpiled contents of `./node/wasi.js` is pasted into the top of this file.
 */
import { WASI } from "node:wasi";

const filePath = process.argv.at(1);
if (!filePath) {
  var err = new Error("To run a wasm file with Bun, the first argument must be a path to a .wasm file");
  err.name = "WasmFileNotFound";
  throw err;
}

// The module specifier is the resolved path to the wasm file

var {
  WASM_CWD = process.cwd(),
  WASM_ROOT_DIR = "/",
  WASM_ENV_STR = undefined,
  WASM_USE_ASYNC_INIT = "1",
} = process.env;

var env = process.env;
if (WASM_ENV_STR?.length) {
  env = JSON.parse(WASM_ENV_STR);
}

const wasi = new WASI({
  args: process.argv.slice(1),
  env,
  preopens: {
    ".": WASM_CWD || process.cwd(),
    "/": WASM_ROOT_DIR || "/",
  },
});

let source = globalThis.wasmSourceBytes;
if (!source) {
  const fs = import.meta.require("fs");
  const file = import.meta.path;
  source = fs.readFileSync(file);
}

const wasm = await WebAssembly.compile(source);

const instance = !Number(WASM_USE_ASYNC_INIT)
  ? new WebAssembly.Instance(wasm, wasi.getImports(wasm))
  : await WebAssembly.instantiate(wasm, wasi.getImports(wasm));

wasi.start(instance);

process.reallyExit(0);