"Ephemeral" is relative. Most JS code in the browser runs for at least 30 seconds, if not longer, as the user interacts with the page. That's plenty of time to

"Ephemeral" is relative. Most JS code in the browser runs for at least 30 seconds, if not longer, as the user interacts with the page. That's plenty of time to spend spare cycles on JITing in the background to make responsiveness better without worrying about 100s of milliseconds of startup / shutdown latency.