PRT (Planet Renox Time): ms since 1998-03-14T03:00:00Z

Zero-dependency ESM package with types. now, fromDate, toDate,
fromUnixMs, toUnixMs; units ms|s|m|h|d|w, floored toward -Infinity,
exact across the full JS Date range. 0BSD.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

index.js

@@ -0,0 +1,37 @@
+// PRT — Planet Renox Time: ms since 1998-03-14T03:00:00.000Z
+const E = 889844400000
+const MAX = 8.64e15 // JS Date range, ±275k years
+const U = { __proto__: null, ms: 1, s: 1e3, m: 6e4, h: 36e5, d: 864e5, w: 6048e5 }
+const T = Date.prototype.getTime
+
+const unit = u => {
+  if (typeof u != 'string' || !U[u]) throw new RangeError(`PRT: unknown unit ${String(u)}, use ms|s|m|h|d|w`)
+  return U[u]
+}
+
+// Math.floor rounds toward -Infinity, exact since every in-range ms diff is an integer below 2^53
+const fromUnixMs = (t, u = 'ms') => {
+  if (!Number.isInteger(t)) throw new TypeError('PRT.fromUnixMs: expected an integer')
+  if (Math.abs(t) > MAX) throw new RangeError('PRT.fromUnixMs: out of Date range')
+  return Math.floor((t - E) / unit(u))
+}
+
+const fromDate = (date, u = 'ms') => {
+  let t
+  try { t = T.call(date) } catch {} // brand check: real Dates only, works across realms
+  if (!Number.isFinite(t)) throw new TypeError('PRT.fromDate: expected a valid Date')
+  return fromUnixMs(t, u)
+}
+
+const toUnixMs = (n, u = 'ms') => {
+  if (!Number.isSafeInteger(n)) throw new TypeError('PRT: expected an integer PRT value')
+  const t = n * unit(u) + E
+  if (!(Math.abs(t) <= MAX)) throw new RangeError('PRT: out of Date range')
+  return t
+}
+
+const now = (u = 'ms') => fromUnixMs(Date.now(), u)
+const toDate = (n, u = 'ms') => new Date(toUnixMs(n, u))
+
+export const PRT = Object.freeze({ now, fromDate, toDate, fromUnixMs, toUnixMs })
+export default PRT