HTML - HTML Web Workers

HTML Web Workers allow JavaScript code to run in the background without affecting the performance of the web page. Normally, JavaScript runs on a single thread, which means heavy tasks can make the webpage slow or unresponsive. Web Workers solve this problem by running scripts in a separate background thread.

Why Web Workers Are Needed

When a webpage performs complex operations such as large calculations, data processing, or file handling, the browser interface may freeze. Users may experience delayed clicks, scrolling problems, or page lag. Web Workers help prevent this by moving time-consuming tasks away from the main execution thread.

How Web Workers Work

A Web Worker runs a separate JavaScript file independently from the main webpage. Communication between the main page and the worker happens through messages.

The main page sends data to the worker, and the worker processes the data and sends the result back.

Creating a Web Worker

Step 1: Create a worker file (worker.js)

self.onmessage = function(event) {
    let result = event.data * 2;
    self.postMessage(result);
};

Step 2: Create the worker in the HTML page

let worker = new Worker("worker.js");

worker.postMessage(10);

worker.onmessage = function(event) {
    console.log("Result:", event.data);
};

Communication Method

Web Workers use message passing instead of shared variables.

postMessage() is used to send data.
onmessage is used to receive data.

This approach improves safety because the worker cannot directly access the webpage’s variables.

Types of Web Workers

Dedicated Worker
Used by a single webpage or script.

Shared Worker
Can be used by multiple browser tabs or windows from the same origin.

Service Worker
Works as a background process mainly for caching, offline support, and progressive web apps.

Limitations of Web Workers

Web Workers cannot access the DOM directly.
They cannot manipulate HTML elements or UI components.
They must communicate through messages only.

Advantages of Web Workers

Improves webpage performance.
Prevents browser freezing.
Allows parallel background processing.
Enhances user experience in heavy applications.

Common Use Cases

Large mathematical calculations.
Real-time data processing.
Image or video processing.
Background data synchronization.
Handling large datasets without blocking the interface.

HTML Web Workers are an important feature for building fast, responsive, and modern web applications where performance and smooth user interaction are required.