Web workers demo from https://developer.mozilla.org/en-US/docs/DOM/Using_web_workers

main.js

var worker = new Worker('my_task.js');
worker.onmessage = function(event) {
 console.log("Worker said : " + event.data);
};
worker.postMessage('ali');

my_task.js

self.postMessage("I'm working befor postMessage('ali').");
self.onmessage = function(event) {
  self.postMessage('Hi '+event.data);
};