[nodejs][worker_threads] async req/res to Worker with MessageChannel

main.js

// node.js worker_threads module example: main thread side
//$ node --exprimental-worker main.js
const path = require("path");
const {Worker, MessageChannel} = require("worker_threads");

//NOTE: worker code accepts only absolute file path
//      not URLs includes "data:" URL
const w = new Worker(path.resolve(__dirname, "./worker.js"));
(async () => {
    console.log(await send(w, "Hello"));
    console.log(await send(w, "World"));
    w.terminate();
})().catch(console.error);

// req/res style communication to workers
async function send(worker, data) {
    const mc = new MessageChannel();
    const res =  new Promise(resolve => {
        mc.port1.once("message", ({data}) => resolve(data));
    });

    // Worker and Port uses node.js EventEmitter, not DOM EventTarget
    // No event class, post any objects to serializable
    //  passing ports explicitly on the first argument:
    // It should also set second ports args
    const ports = [mc.port2];
    worker.postMessage({data, ports}, ports);
    return await res;
}

worker.js

// node.js worker_threads example: worker side code
// NOTE: in main, parentPort is null
const {parentPort} = require("worker_threads");

// As DOM MessageEvent style parameters
parentPort.on("message", ({data, ports}) => {
    // echo response also as a MessageEvent like
    ports[0].postMessage({data, ports: []});
});

worker_threads: node.js >= 10.5

• https://nodejs.org/api/worker_threads.html