Temporal in Production: Field Notes on Replacing JavaScript Date, the Same-Day Bug, and What Doesn't Cross the RSC Boundary

Headline: Temporal is the TC39 API that replaces JavaScript's Date object with immutable, time-zone-aware types. The migration is mechanical almost everywhere, except at two boundaries: a Temporal object cannot be passed as a prop from a Server Component to a Client Component, and it has to become a string again before it reaches a database driver.

I have written the same date bug at least four times in my career. A user in Cairo files a report at 22:30 on the 22nd, the serverless function runs in UTC, and the dashboard files it under the 21st. Every time, the fix was a patch on top of Date — a helper, a library, an offset subtracted somewhere hopeful. This year I stopped patching and moved a Next.js app's date handling onto Temporal instead.

Key takeaways

Temporal replaces Date, not Intl. Temporal owns arithmetic, comparison, and time zones; Intl.DateTimeFormat still does the human-facing formatting, and every Temporal object exposes toLocaleString().

Choose the Temporal type by what the value means. A birthday is a Temporal.PlainDate, an audit timestamp is a Temporal.Instant, and "3pm in Cairo" is a Temporal.ZonedDateTime.