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What is a Web Worker in HTML5?

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

When executing scripts in an HTML page, the page becomes unresponsive until the script is finished. 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.
Check Web Worker Support Before creating a web worker.
if (typeof(Worker) !== "undefined")
{ // Web worker supported
 // Web Worker  not supporting.

Create a Web Worker File  in an external JavaScript.
var i = 0;
 function timedCount()
 i = i + 1; postMessage(i);

The important part of the code above is the postMessage() method - which is used to post a message back to the HTML page.
To create a Web Worker Object The following lines checks if the worker already exists:
if (typeof(w) == "undefined")
 w = new Worker("demo_workers.js");

Add an "onmessage" event listener to the web worker.
w.onmessage = function(event){
document.getElementById("result").innerHTML = event.data;

o terminate a web worker, and free browser/computer resources the terminate() method is used.

After  termination  reuse the code:
w = undefined;
Web Worker
Tech writer at newsandstory
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