Polyfill: Extract addDaysISO from calendar helpers

Adding days to an ISO date does not have any calendar-specific behaviour
so extract it out of the calendar helper objects. There were also some
calls with a leftover cache parameter which was unused.

Author: ptomato

polyfill/lib/calendar.mjs

@@ -151,6 +151,10 @@ function ISODateSurpasses(sign, baseDate, isoDate2, years, months, weeks, days)
   return false;
 }
 
+function addDaysISO(isoDate, days) {
+  return ES.BalanceISODate(isoDate.year, isoDate.month, isoDate.day + days);
+}
+
 const impl = {};
 
 impl['iso8601'] = {
@@ -844,7 +848,7 @@ const nonIsoHelperBase = {
       // that's currently worked around by a custom calendarToIsoDate
       // implementation in those calendars. So this optimization should be safe
       // for all ICU calendars.
-      let testIsoEstimate = this.addDaysIso(isoEstimate, diffDays);
+      let testIsoEstimate = addDaysISO(isoEstimate, diffDays);
       if (date.day > this.minimumMonthLength(date)) {
         // There's a chance that the calendar date is out of range. Throw or
         // constrain if so.
@@ -854,7 +858,7 @@ const nonIsoHelperBase = {
             throw new RangeErrorCtor(`day ${day} does not exist in month ${month} of year ${year}`);
           }
           // Back up a day at a time until we're not hanging over the month end
-          testIsoEstimate = this.addDaysIso(testIsoEstimate, -1);
+          testIsoEstimate = addDaysISO(testIsoEstimate, -1);
           testCalendarDate = this.isoToCalendarDate(testIsoEstimate, cache);
         }
       }
@@ -865,7 +869,7 @@ const nonIsoHelperBase = {
     let diff = simpleDateDiff(date, roundtripEstimate);
     if (diff.years !== 0 || diff.months !== 0 || diff.days !== 0) {
       const diffTotalDaysEstimate = diff.years * 365 + diff.months * 30 + diff.days;
-      isoEstimate = this.addDaysIso(isoEstimate, diffTotalDaysEstimate);
+      isoEstimate = addDaysISO(isoEstimate, diffTotalDaysEstimate);
       roundtripEstimate = this.isoToCalendarDate(isoEstimate, cache);
       diff = simpleDateDiff(date, roundtripEstimate);
       if (diff.years === 0 && diff.months === 0) {
@@ -878,7 +882,7 @@ const nonIsoHelperBase = {
     // distance to the target, starting with 8 days per step.
     let increment = 8;
     while (sign) {
-      isoEstimate = this.addDaysIso(isoEstimate, sign * increment);
+      isoEstimate = addDaysISO(isoEstimate, sign * increment);
       const oldRoundtripEstimate = roundtripEstimate;
       roundtripEstimate = this.isoToCalendarDate(isoEstimate, cache);
       const oldSign = sign;
@@ -905,7 +909,7 @@ const nonIsoHelperBase = {
               // To constrain, pick the earliest value
               const order = this.compareCalendarDates(roundtripEstimate, oldRoundtripEstimate);
               // If current value is larger, then back up to the previous value.
-              if (order > 0) isoEstimate = this.addDaysIso(isoEstimate, -1);
+              if (order > 0) isoEstimate = addDaysISO(isoEstimate, -1);
               sign = 0;
             }
           }
@@ -936,13 +940,9 @@ const nonIsoHelperBase = {
     const isoDate = this.calendarToIsoDate(calendarDate, overflow, cache);
     return this.isoToCalendarDate(isoDate, cache);
   },
-  addDaysIso(isoDate, days) {
-    const added = ES.BalanceISODate(isoDate.year, isoDate.month, isoDate.day + days);
-    return added;
-  },
   addDaysCalendar(calendarDate, days, cache) {
     const isoDate = this.calendarToIsoDate(calendarDate, 'constrain', cache);
-    const addedIso = this.addDaysIso(isoDate, days);
+    const addedIso = addDaysISO(isoDate, days);
     const addedCalendar = this.isoToCalendarDate(addedIso, cache);
     return addedCalendar;
   },
@@ -956,7 +956,7 @@ const nonIsoHelperBase = {
           ? -MathMax(day, this.daysInPreviousMonth(calendarDate, cache))
           : this.daysInMonth(calendarDate, cache);
       const isoDate = this.calendarToIsoDate(calendarDate, 'constrain', cache);
-      let addedIso = this.addDaysIso(isoDate, days, cache);
+      let addedIso = addDaysISO(isoDate, days);
       calendarDate = this.isoToCalendarDate(addedIso, cache);
 
       // Normally, we can advance one month by adding the number of days in the
@@ -967,7 +967,7 @@ const nonIsoHelperBase = {
       if (months > 0) {
         const monthsInOldYear = this.monthsInYear(oldCalendarDate, cache);
         while (calendarDate.month - 1 !== month % monthsInOldYear) {
-          addedIso = this.addDaysIso(addedIso, -1, cache);
+          addedIso = addDaysISO(addedIso, -1);
           calendarDate = this.isoToCalendarDate(addedIso, cache);
         }
       }
@@ -1062,11 +1062,11 @@ const nonIsoHelperBase = {
     // Add enough days to get into the next month, without skipping it
     const increment = day <= max - min ? max : min;
     const isoDate = this.calendarToIsoDate(calendarDate, 'constrain', cache);
-    const addedIsoDate = this.addDaysIso(isoDate, increment);
+    const addedIsoDate = addDaysISO(isoDate, increment);
     const addedCalendarDate = this.isoToCalendarDate(addedIsoDate, cache);
 
     // Now back up to the last day of the original month
-    const endOfMonthIso = this.addDaysIso(addedIsoDate, -addedCalendarDate.day);
+    const endOfMonthIso = addDaysISO(addedIsoDate, -addedCalendarDate.day);
     const endOfMonthCalendar = this.isoToCalendarDate(endOfMonthIso, cache);
     return endOfMonthCalendar.day;
   },
@@ -1083,7 +1083,7 @@ const nonIsoHelperBase = {
     if (min === max) return max;
 
     const isoDate = this.calendarToIsoDate(calendarDate, 'constrain', cache);
-    const lastDayOfPreviousMonthIso = this.addDaysIso(isoDate, -day);
+    const lastDayOfPreviousMonthIso = addDaysISO(isoDate, -day);
     const lastDayOfPreviousMonthCalendar = this.isoToCalendarDate(lastDayOfPreviousMonthIso, cache);
     return lastDayOfPreviousMonthCalendar.day;
   },