Web Workers are a powerful feature in JavaScript that allow you to run scripts in the background (parallel to the main thread) to perform time-consuming tasks without blocking the user interface. This can significantly improve the responsiveness and performance of web applications, especially when dealing with heavy computations or lengthy operations.

Web Workers have their own dedicated thread and do not share the same memory space with the main thread, ensuring that they don't interfere with the UI responsiveness. Communication between the main thread and web workers is achieved using a messaging system.

Here's an example to illustrate how to use Web Workers:

1. **main.js** (Main Thread):

```js

// Creating a new Web Worker

const myWorker = new Worker('worker.js');

// Send a message to the worker

myWorker.postMessage({ number: 10 });

// Receive message from the worker

myWorker.onmessage = function(event) {

console.log('Result from Web Worker:', event.data);

};

```

2. **worker.js** (Web Worker):

```js

// Listen for messages from the main thread

self.onmessage = function(event) {

const number = event.data.number;

const result = performCalculation(number);

// Sending the result back to the main thread

self.postMessage(result);

};

// Function to perform a time-consuming calculation

function performCalculation(number) {

let sum = 0;

for (let i = 1; i <= number; i++) {

sum += i;

}

return sum;

}

```

In this example, we have a main script (**main.js**) that creates a new Web Worker by providing the URL of the script (**worker.js**) that will run in the background. The main thread sends a message to the Web Worker using `postMessage` and listens for messages from the Web Worker using the `onmessage` event.

The Web Worker (**worker.js**) listens for messages from the main thread using `self.onmessage`. When a message is received, it performs a time-consuming calculation using the `performCalculation` function and sends the result back to the main thread using `self.postMessage`.

By using Web Workers, we can perform the heavy calculation in the background without blocking the main thread, ensuring a smooth and responsive user experience.

Please note that Web Workers have some limitations, such as not having access to the DOM, the window object, and certain APIs, as they run in a separate thread. Therefore, they are best suited for CPU-intensive tasks or operations that don't require direct interaction with the DOM.