A worker's requestAnimationFrame kept drawing to an OffscreenCanvas in a hidden tab: tell the worker

// On the page. `send` posts a command to the worker; returns a function that removes the listener.
function forwardVisibility(send: (method: string, args: unknown[]) => void): () => void {
  const onVisibility = () => send("setVisible", [document.visibilityState !== "hidden"]);
  document.addEventListener("visibilitychange", onVisibility);
  onVisibility();
  return () => document.removeEventListener("visibilitychange", onVisibility);
}
// In the worker's loop.
let paused = false;
let scheduled = false;
function schedule(tick: FrameRequestCallback) {
  if (paused || scheduled) return;
  scheduled = true;
  requestAnimationFrame((t) => { scheduled = false; if (!paused) tick(t); });
}
function setVisible(visible: boolean, tick: FrameRequestCallback) {
  paused = !visible;
  if (visible) schedule(tick);
}