Editorial: Clarify Infinity handling in PlainYearMonth constructor.

Author: Ms2ger

lib/ecmascript.mjs

@@ -150,6 +150,13 @@ const ES2020 = {
 
 export const ES = ObjectAssign({}, ES2020, {
   ToPositiveInteger: ToPositiveInteger,
+  ToFiniteInteger: (value) => {
+    const integer = ES.ToInteger(value);
+    if (!NumberIsFinite(integer)) {
+      throw new RangeError('infinity is out of range');
+    }
+    return integer;
+  },
   IsTemporalInstant: (item) => HasSlot(item, EPOCHNANOSECONDS) && !HasSlot(item, TIME_ZONE, CALENDAR),
   IsTemporalTimeZone: (item) => HasSlot(item, TIMEZONE_ID),
   IsTemporalCalendar: (item) => HasSlot(item, CALENDAR_ID),

lib/plainyearmonth.mjs

@@ -9,10 +9,10 @@ const DISALLOWED_UNITS = ['week', 'day', 'hour', 'minute', 'second', 'millisecon
 
 export class PlainYearMonth {
   constructor(isoYear, isoMonth, calendar = ES.GetISO8601Calendar(), referenceISODay = 1) {
-    isoYear = ES.ToInteger(isoYear);
-    isoMonth = ES.ToInteger(isoMonth);
+    isoYear = ES.ToFiniteInteger(isoYear);
+    isoMonth = ES.ToFiniteInteger(isoMonth);
     calendar = ES.ToTemporalCalendar(calendar);
-    referenceISODay = ES.ToInteger(referenceISODay);
+    referenceISODay = ES.ToFiniteInteger(referenceISODay);
 
     // Note: if the arguments are not passed, ToInteger(undefined) will have returned 0, which will
     //       be rejected by RejectISODate in CreateTemporalYearMonthSlots. This