JavaScript - Web Worker

a web worker is a JavaScript running in the background, without affecting the performance of the page

Example Code

index.html

<!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 src="script.js"></script>
</body>
</html>

script.js

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;
}

web-worker.js

var i = 0;

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

timedCount();