WorkerGlobalScope and DedicatedWorkerGlobalScope #179

Phase 19: Web Workers#

Implement the global object for dedicated worker threads, mirroring how Window is the global for the main thread.

What to implement#

Add crates/js/src/worker_global.rs:

• WorkerGlobalScope base struct providing:

  • self — refers to the global itself
  • location — a WorkerLocation stub (href, protocol, host, pathname, search, hash — read-only snapshot of the URL passed to the Worker constructor)
  • navigator — WorkerNavigator stub (userAgent, hardwareConcurrency)
  • console — forward to the same Console implementation used on the main thread
  • Timer APIs: setTimeout, setInterval, clearTimeout, clearInterval (reuse crates/js/src/timers.rs)
  • fetch — reuse existing fetch implementation
  • atob / btoa
  • queueMicrotask
  • close() — terminates the worker (signals the run-loop to exit)

• DedicatedWorkerGlobalScope extending the above:

  • postMessage(data, transfer?) — serialize via Structured Clone, send to the main thread channel
  • onmessage / onmessageerror — event handler properties
  • Fires a MessageEvent when a message arrives from the main thread

• Worker script execution: after spawning the thread (from the previous issue), fetch the script URL (using the net crate), parse and execute it in a fresh JsContext whose global is a DedicatedWorkerGlobalScope.

Acceptance criteria#

• Worker script can call self.postMessage('hello') and the value arrives on the main thread.
• close() inside a worker terminates the thread cleanly.
• Timer callbacks fire inside the worker run-loop.
• cargo test -p we-js passes.