Explanation/Reference:
* addEventListener
The addEventListener() method attaches an event handler to the specified element.
In context of a worker, both self and this refer to the global scope. The worker can either add an event listener for the message event, or it can define the onmessage handler to listen for any messages sent by the parent thread.
* postmessage
Pass a message to the worker.
* close()
Terminating Workers
Workers are resource-intensive; they are OS-level threads. Therefore, you do no want to create a large number of worker threads, and you should terminate the web worker after it completes its work. Workers can terminate themselves, like this:
self.close();
Reference: HTML DOM addEventListener() Method; The Basics of Web Workers