the year 50 is the year 50, not 1950

new Date(50, 0, 1) is 1950: the Date constructor reads a year of 0..99
as 1900 + n, and the setter does not. This calendar answers from the
year 1, so pascha() for an early year had been quietly reporting a
twentieth-century date.

npm/test.mjs

@@ -129,6 +129,14 @@ check("pascha matches the published dates", () => {
   assert.equal(iso(typikon.pascha(2027, "old")), "2027-05-02");
 });
 
+check("a two-digit year is that year, not 19xx", () => {
+  // The Date constructor reads 0..99 as 1900 + n, which would have made the
+  // Paschalion for the year 50 answer for 1950 without a word.
+  assert.equal(typikon.pascha(50, "old").getFullYear(), 50);
+  assert.equal(typikon.pascha(99, "old").getFullYear(), 99);
+  assert.equal(typikon.pascha(100, "old").getFullYear(), 100);
+});
+
 check("every listed jurisdiction reckons", () => {
   const all = typikon.jurisdictions();
   assert.ok(all.length > 20);

src/wasm.rs

@@ -164,7 +164,14 @@ fn from_js_date(d: &js_sys::Date) -> Result<Date, JsError> {
 
 fn to_js_date(d: Date) -> js_sys::Date {
     let (y, m, day) = d.ymd();
-    js_sys::Date::new_with_year_month_day(y as u32, m as i32 - 1, day as i32)
+    let out = js_sys::Date::new_with_year_month_day(y as u32, m as i32 - 1, day as i32);
+    // `new Date(50, 0, 1)` is 1950, not the year 50: the two-digit-year rule is
+    // in the constructor and not in the setter. This calendar answers from the
+    // year 1, so the rule has to be undone rather than lived with.
+    if (0..=99).contains(&y) {
+        out.set_full_year(y as u32);
+    }
+    out
 }
 
 // ──────────────────────────────── the api ─────────────────────────────────