Web Workers
Web Workers are a JavaScript API that enables running scripts in the background without blocking the main thread.
What
Web Workers improve performance by offloading resource-intensive tasks, allowing the main thread to remain responsive and preventing UI freezes.
Why
How
- Create a new Worker object
- Specify the script file to run in the background
- Communicate with the worker using messages
Since
3 April
2009
Support
Since
Internet Explorer 10
Firefox 3.5
Chrome 4
Safari 4
How
Why
Browser
Main Thread
Worker
TBT
Total Blocking Time
Why
FID
First Input Delay
Why
INP
Interaction to Next Paint
Why
How
<html>
<head>
<title>Web Workers Hello World</title>
<script src="main.js"></script>
</head>
</html>index.html
How
const worker = new Worker('worker.js');
worker.onmessage = (msg) => {
console.log('message received from worker', msg.data);
};
worker.postMessage('message sent to worker');main.js
How
self.onmessage = (msg) => {
console.log('message from main', msg.data);
postMessage('message sent from worker');
};worker.js
Types
Dedicated Worker
Shared Worker
Exclusive execution context
A Dedicated Worker is associated with a single JavaScript script and has its own isolated execution context.
Use
Dedicated Workers are useful when you have a specific task that should not share data or resources with other Workers, and only one script needs to access them.
Shared execution context
A Shared Worker can be shared among multiple scripts in different browser windows or tabs.
Use
Are useful when you want to share data or resources between multiple script instances in different browsing contexts, such as in a multi-user web application or in an application that uses multiple browser tabs or windows.
new Worker('worker.js')new SharedWorker('worker.js')How
const worker = new SharedWorker('shared-worker.js');main.js
Shared Worker
What
Dedicated Worker
- Image and video processing
- Scientific and mathematical calculations
- File uploading and processing
- Geolocation and mapping
- Online games
- Artificial intelligence and machine learning on the web
- Real-time data analysis and processing
- Encryption and security
What
Shared Worker
- Real-time collaborative applications
- Push notifications
- Session management and authentication
- Shared caching
- Multiplayer online games
- Data analysis and event tracking
- Communication between windows or tabs
- Real-time user interface updates
Code
Dedicated Worker
// Create a Dedicated Worker
const worker = new Worker('worker.js');
// Define a function to handle Worker messages
worker.onmessage = function (e) {
console.log('Processed data:', e.data);
};
// Send a network request to the Worker
const apiUrl = 'https://api.example.com/data';
worker.postMessage({ type: 'fetch', url: apiUrl });
Process Data in a Worker
main.js
Code
Dedicated Worker
// Handle main thread messages
self.onmessage = function (e) {
const message = e.data;
if (message.type === 'fetch') {
// Make a network request
fetch(message.url)
.then((response) => response.json())
.then((data) => {
// Perform data processing
const processedData = processData(data);
// Send processed data back to main thread
self.postMessage(processedData);
})
.catch((error) => {
console.error('Error al obtener datos:', error);
});
}
};
// Function to process data (just as an example)
function processData(data) {
// Here you can perform any necessary processing
// on the data.
// For example, filtering, transforming or adding
// additional information.
// Return processed data
return { processed: true, data };
}
Process Data in a Worker
worker.js
Don't
Access to...
- DOM (Document Object Model)
- Global Variables of the Main Thread
- Objects Related to the Browser Environment
- Direct Interaction with User Events
- Browser History Manipulation
- Access to Most Web Platform APIs
- Direct Access to Local or External Resources