Promise vs Timer

Console output or cleanup runs in an order that does not match the source code order. Promise-based state updates can happen before scheduled timers and animation cleanup.

Treating all async callbacks as the same queue.

Make ordering explicit instead of relying on when a queued callback might happen to run.

Promise.resolve().then(handleMicrotask);
setTimeout(handleTimer, 0);
// Assert/expect the microtask before the timer.

The console lane proves the visible order: A -> D -> C -> B. The active line and queues show why source order changed.

Add temporary logs around the sync line, promise callback, and timer, then confirm the order without adding arbitrary delays.