Web Workers
Any CPU-intensive work (parsing, compression, crypto, WASM) must run off the main thread to keep UI responsive. Workers are the browser's concurrency primitive — understand their message passing model and limitations (no DOM access).
What It Defines
Dedicated and Shared Workers: background JavaScript execution threads that don't block the main thread. Communicate via postMessage/structured clone. Dedicated Workers are per-creator; Shared Workers are per-origin and shared across tabs.
Canonical (Normative)
Convenient (Practical)
Maintains the living standards for the web platform: HTML, DOM, Fetch, URL, Streams, and more. These are continuously updated living documents, not versioned snapshots.
Related Specs
The spec behind every HTML page, form, and browser API. The canonical reference for how browsers actually parse and process HTML.
JavaScript is the execution model of the web. The spec is the canonical reference for language semantics — closures, coercion, prototype lookup, module resolution, and async scheduling.
Service Workers power offline support, background sync, and push notifications. Required for serious PWA/installable app behavior.