demo.js

import { fileURLToPath } from "node:url";
import { createServer as createNetServer } from "node:net";
import { env } from "node:process";
import { stat } from "node:fs/promises";
import { spawn } from "node:child_process";

import terminate from "terminate";

/** Where to find Jco as an executable */
const JCO_PATH = env.JCO_PATH ?? "jco";

/** Path to the WASM file to be used */
const WASM_PATH = fileURLToPath(
  new URL(env.WASM_PATH ?? "./component.wasm", import.meta.url),
);

async function main() {
  // Determine paths to jco and output wasm
  const wasmPathExists = await stat(WASM_PATH)
    .then((p) => p.isFile())
    .catch(() => false);
  if (!wasmPathExists) {
    throw new Error(
      `Missing/invalid Wasm binary @ [${WASM_PATH}] (has 'npm run build' been run?)`,
    );
  }

  // Generate a random port
  const randomPort = await getRandomPort();

  // Spawn jco serve
  const proc = spawn(JCO_PATH, ["serve", "--port", randomPort, WASM_PATH], {
    detached: false,
    stdio: "pipe",
    shell: false,
  });

  // Wait for the server to start
  await new Promise((resolve) => {
    proc.stderr.on("data", (data) => {
      if (data.includes("Server listening")) {
        resolve();
      }
    });
  });

  // Execute the WASM module running via jco serve
  try {
    const resp = await fetch(`http://localhost:${randomPort}`);
    const respText = await resp.text();
    console.log(`fetch() OUTPUT:\n${respText}`);
  } catch (err) {
    throw err;
  } finally {
    await terminate(proc.pid);
  }
}

// Utility function for getting a random port
export async function getRandomPort() {
  return await new Promise((resolve) => {
    const server = createNetServer();
    server.listen(0, function () {
      const port = this.address().port;
      server.on("close", () => resolve(port));
      server.close();
    });
  });
}

await main();