Read a Retry-After header

Turn delay-seconds or an HTTP date into milliseconds to wait, never negative.

JavaScript Version 1.0.0 · MIT · by Oveyon · .md

function retryAfterMs({ retryAfter, date }) { const seconds = Number(retryAfter); return Math.max(0, Number.isFinite(seconds) ? seconds * 1000 : Date.parse(retryAfter) - Date.parse(date)); }

Input & expected output

{
  "retryAfter": "30",
  "date": "Wed, 28 Oct 2026 14:00:00 GMT"
}

30000

The edge case

{
  "retryAfter": "Wed, 28 Oct 2026 14:00:30 GMT",
  "date": "Wed, 28 Oct 2026 14:00:00 GMT"
}

30000

Know the limits

• An HTTP date is compared with the response’s own Date header, not your clock, so clock skew cannot shorten the wait. The lab accepts delay-seconds from 0 to 86,400.
• Oveyon answers rate limiting with HTTP 429 and Retry-After. Wait at least this long, then retry with the same idempotency key.

The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.

Keep exploring

• Convert an email domain to punycode — Keep the local part and convert an international domain to its ASCII xn-- form.
• Get the domain of an email address — Take the part after the last @ and lowercase it, for domain checks and grouping.
• Mask an email address for logs — Keep the first character and the domain; hide the rest of the local part.