The key output order is render start -> render end -> message. Incoming events wait until the current JavaScript stack is clear.
A production symptom appears first: flaky tests, stale state, slow UI, late cleanup, or growing memory. This affects live dashboards, chats, trading screens, collaborative apps, and real-time notifications.
Expecting network events to interrupt CPU-heavy work.
Fix the root scheduling, cleanup, or concurrency pattern instead of adding arbitrary waits.
try {
await operation();
} finally {
cleanup();
}The console lane proves the visible order: render start -> render end -> message. The active line and queues show why source order changed.
Reproduce the symptom with a small test, apply the safer pattern, then verify the flaky, slow, or leaking behavior disappears.
Related cases
Continue with nearby confusion while the mental model is fresh.
React batched state log
This shows up in React forms, counters, analytics events, and logic that reads state immediately after updating it.
Effect cleanup race
This prevents wrong profile data, flickering search results, and stale route content in React apps.
Stale closure timeout
This affects delayed notifications, retry callbacks, telemetry, and timeout-based cleanup logic.
Was this clear?
This stays local for now. It helps you track where the product still needs sharper cases.