Web Workers API - Web APIs | MDN

Web Workers API Overview

• Core Functionality: Enables running script operations in a background thread, preventing laborious processing from blocking the main UI thread.
• Execution: Workers are created via a constructor (e.g., Worker()) and execute a specified JavaScript file.
• Communication: Data is exchanged between the main thread and workers using postMessage() and the onmessage event handler. Data is copied, not shared.
• Limitations: Workers cannot directly manipulate the DOM and lack access to certain default methods/properties of the Window object.
• Capabilities:
  • Can spawn new workers (same-origin policy applies).
  • Can perform network requests using fetch() or XMLHttpRequest.
  • Access to standard JavaScript functions (String, Array, JSON, etc.).
• Types of Workers:
  • Dedicated Workers: Utilized by a single script; represented by DedicatedWorkerGlobalScope.
  • Shared Workers: Accessible by multiple scripts across different windows/iframes within the same domain; requires communication via an active port.
  • Service Workers: Act as proxy servers to enable offline experiences, intercept network requests, and manage push notifications/background sync.
• Key Interfaces:
  • Worker: Represents the running thread.
  • WorkerGlobalScope: The base interface for worker contexts (similar to Window for main content).
  • WorkerLocation: Defines the absolute location of the executed script.
• Global Scope: While Window is unavailable, workers use WorkerGlobalScope-derived contexts (DedicatedWorkerGlobalScope, SharedWorkerGlobalScope, ServiceWorkerGlobalScope) which share many methods via the WindowOrWorkerGlobalScope mixin.