What are workers in JavaScript used for?

Workers in JavaScript are background threads that allow you to run scripts in parallel with the main execution thread, without blocking or interfering with the user interface. Their key features include:

• Parallel processing: Workers run in a separate thread from the main thread, allowing your web page to remain responsive to user interactions while the worker performs its tasks. It's useful for moving CPU-intensive work off the main thread and freeing you from JavaScript's single-threaded nature.
• Communication: Uses postMessage() and onmessage/'message' event for messaging.
• Access to web APIs: Workers have access to various Web APIs, including fetch(), IndexedDB, and Web Storage, allowing them to perform tasks like data fetching and persisting data independently.
• No DOM access: Workers cannot directly manipulate the DOM, thus cannot interact with the UI, ensuring they don't accidentally interfere with the main thread's operation.

There are three main types of workers in JavaScript:

• Web workers / Dedicated workers
  • Run scripts in background threads, separate from the main UI thread.
  • Useful for CPU-intensive tasks like data processing, calculations, etc.
  • Cannot directly access or manipulate the DOM.
• Service workers
  • Act as network proxies, handling requests between the app and network.
  • Enable offline functionality, caching, and push notifications.
  • Run independently of the web page, even when it's closed.
• Shared workers
  • Can be shared by multiple scripts running in different windows or frames, as long as they're in the same domain.
  • Scripts communicate with the shared worker by sending and receiving messages.
  • Useful for coordinating tasks across different parts of a web page.