Make a daily puzzle

Choose the calendar explicitly

UTC gives everyone the same date boundary. Name an IANA zone for a puzzle that changes at one place’s midnight. dayKey, dailySeed and nextDayStart use that calendar rather than assuming a day is always 24 hours.

import { dailySeed, dayKey, dayOfSeed, daySeed, nextDayStart } from "@johnmorrisdotca/tane";

const at = new Date("2026-10-11T03:00:00Z");
console.log(dayKey(at, "UTC"), dayKey(at, "America/Toronto"));
console.log(dailySeed(at, "UTC"));
console.log(nextDayStart(at, "America/Toronto").toISOString());
const block = { from: 1000000000, size: 100000000 };
console.log(dayOfSeed(daySeed("2026-10-11", block), block));

2026-10-11 2026-10-10
20261011
2026-10-11T04:00:00.000Z
2026-10-11

Reserve a daily range

daySeed places the YYYYMMDD number inside a SeedBlock; the block must be large enough for that decimal offset. dayOfSeed reverses it or returns null when the seed names no real day. Reserve the same block when drawing non-daily seeds so the ranges stay separate.

Keep a page open

The React daily hook refreshes at the chosen zone’s midnight. For a pure engine host, use nextDayStart to find the boundary and let the host control refresh. The hooks and seed ranges describe those distinct jobs.