# Web Workers
Confidence: high
Last verified: 2026-05-22
Generation: human_only


## TL;DR

Web Workers enable JavaScript to run in background threads, parallelizing CPU-intensive tasks without blocking the main UI thread. They communicate with the main thread via message passing (`postMessage`), not shared memory (by default).

## Core Explanation

Types: Dedicated Workers (single tab), Shared Workers (multiple tabs/windows), and Service Workers (specialized proxy). Workers have no DOM access but can use `fetch`, WebSocket, IndexedDB, and most browser APIs. Communication uses structured cloning (copy) or Transferable objects (zero-copy with ownership transfer).

## Further Reading

- [Web Workers (WHATWG)](https://html.spec.whatwg.org/multipage/workers.html)