OffscreenCanvas was already a type.

Author: samouri

src/worker-thread/WorkerDOMGlobalScope.ts

@@ -110,7 +110,7 @@ export interface GlobalScope {
   // implementation to enable setting readonly properties like currentTarget.
   Event: typeof WorkerDOMEvent;
   MutationObserver: typeof MutationObserver;
-  OffscreenCanvas?: typeof OffscreenCanvas;
+  OffscreenCanvas?: OffscreenCanvas; // Refers to the type defined in lib.webworker.d.ts
   ImageBitmap?: typeof ImageBitmap;
   requestAnimationFrame: typeof requestAnimationFrame;
   cancelAnimationFrame: typeof cancelAnimationFrame;