1. Web Worker

A web worker is a JavaScript that runs in the background, independently of other scripts, without affecting the performance of the page. You can continue to do whatever you want: clicking, selecting things, etc., while the web worker runs in the background.

1.1. Web worker demo

// demo_workers.js
var i = 0;

function timedCount() {
  i = i + 1;
  postMessage(i);
  setTimeout(timedCount, 500);
}

timedCount();

<!DOCTYPE html>
<html>
<body>

<p>Count numbers: <output id="result"></output></p>
<button onclick="startWorker()">Start Worker</button>
<button onclick="stopWorker()">Stop Worker</button>

<script>
var w;

function startWorker() {
    if(typeof(Worker) !== "undefined") {
        if(typeof(w) == "undefined") {
            w = new Worker("demo_workers.js");
        }
        w.onmessage = function(event) {
            document.getElementById("result").innerHTML = event.data;
        };
    } else {
        document.getElementById("result").innerHTML = "Sorry! No Web Worker support.";
    }
}

function stopWorker() {
    w.terminate();
    w = undefined;  // can reuse the Web Worker when calling startWorker() again
}
</script>

</body>
</html>

1.2. reference

https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers

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