webWorker.js

//---main.js
if (window.Worker) {

    //worker(aURL, options)
    const worker = new Worker("worker.js");

    worker.onmessage = e => {
        const msg = e.data;
        console.log(`From Worker thread: ${msg}`);
    };

    worker.postMessage("Tom!");


    //worker.terminate();
}
//---end of Main.js

//----- worker.js
onmessage = e => {
    const message = e.data;
    console.log(`From Main thread: ${message}`);

    postMessage("Cat!");
};

//close();
//----end of worker.js