Revert "Remove era from main spec"

This partially reverts commit a7322a6.
'era' is still not present in the spec text, but is present in the
polyfill since this environment includes Intl.

Closes: #1046

docs/plaindate.md

@@ -167,6 +167,11 @@ date.day;   // => 24
 
 The `calendar` read-only property gives the calendar that the `year`, `month`, and `day` properties are interpreted in.
 
+### date.**era** : unknown
+
+The `era` read-only property is `undefined` when using the ISO 8601 calendar.
+It's used for calendar systems that specify an era in addition to the year.
+
 ### date.**dayOfWeek** : number
 
 The `dayOfWeek` read-only property gives the weekday number that the date falls on.

docs/plaindatetime.md

@@ -232,6 +232,11 @@ dt.nanosecond;  // => 500
 
 The `calendar` read-only property gives the calendar that the `year`, `month`, `day`, `hour`, `minute`, `second`, `millisecond`, `microsecond`, and `nanosecond` properties are interpreted in.
 
+### datetime.**era** : unknown
+
+The `era` read-only property is `undefined` when using the ISO 8601 calendar.
+It's used for calendar systems that specify an era in addition to the year.
+
 ### datetime.**dayOfWeek** : number
 
 The `dayOfWeek` read-only property gives the weekday number that the date falls on.

docs/plainyearmonth.md

@@ -159,6 +159,11 @@ ym.month; // => 6
 
 The `calendar` read-only property gives the calendar that the `year` and `month` properties are interpreted in.
 
+### yearmonth.**era** : unknown
+
+The `era` read-only property is `undefined` when using the ISO 8601 calendar.
+It's used for calendar systems that specify an era in addition to the year.
+
 ### yearMonth.**daysInMonth** : number
 
 The `daysInMonth` read-only property gives the number of days in the month.

docs/zoneddatetime.md

@@ -404,6 +404,11 @@ zdt.with({ timeZone: 'GMT' }).timeZone;
 ```
 <!-- prettier-ignore-end -->
 
+### zonedDateTime.**era** : unknown
+
+The `era` read-only property is `undefined` when using the ISO 8601 calendar.
+It's used for calendar systems that specify an era in addition to the year.
+
 ### zonedDateTime.**dayOfWeek** : number
 
 The `dayOfWeek` read-only property gives the weekday number that the date falls on.

polyfill/lib/calendar.mjs

@@ -4,9 +4,7 @@ import { ES } from './ecmascript.mjs';
 import { GetIntrinsic, MakeIntrinsicClass, DefineIntrinsic } from './intrinsicclass.mjs';
 import * as REGEX from './regex.mjs';
 import {
-  CALENDAR,
   CALENDAR_ID,
-  INSTANT,
   ISO_YEAR,
   ISO_MONTH,
   ISO_DAY,
@@ -16,7 +14,6 @@ import {
   ISO_MILLISECOND,
   ISO_MICROSECOND,
   ISO_NANOSECOND,
-  TIME_ZONE,
   CreateSlots,
   GetSlot,
   HasSlot,
@@ -110,6 +107,10 @@ export class Calendar {
     void date;
     throw new Error('not implemented');
   }
+  era(date) {
+    void date;
+    throw new Error('not implemented');
+  }
   dayOfWeek(date) {
     void date;
     throw new Error('not implemented');
@@ -361,6 +362,10 @@ class ISO8601Calendar extends Calendar {
     if (!HasSlot(date, ISO_DAY)) date = ES.ToTemporalDate(date, GetIntrinsic('%Temporal.PlainDate%'));
     return GetSlot(date, ISO_DAY);
   }
+  era(date) {
+    if (!HasSlot(date, ISO_YEAR)) date = ES.ToTemporalDate(date, GetIntrinsic('%Temporal.Date%'));
+    return undefined;
+  }
   hour(time) {
     if (!ES.IsTemporalCalendar(this)) throw new TypeError('invalid receiver');
     return GetSlot(time, ISO_HOUR);
@@ -433,29 +438,6 @@ MakeIntrinsicClass(ISO8601Calendar, 'Temporal.ISO8601Calendar');
 // proposal for ECMA-262. These calendars will be standardized as part of
 // ECMA-402.
 
-function addCustomPropertyGetter(type, name) {
-  Object.defineProperty(GetIntrinsic(`%Temporal.${type}.prototype%`), name, {
-    get() {
-      return GetSlot(this, CALENDAR)[name](this);
-    },
-    configurable: true
-  });
-}
-
-function addEraProperties() {
-  addCustomPropertyGetter('PlainDate', 'era');
-  addCustomPropertyGetter('PlainDateTime', 'era');
-  addCustomPropertyGetter('PlainYearMonth', 'era');
-  Object.defineProperty(GetIntrinsic('%Temporal.ZonedDateTime.prototype%'), 'era', {
-    get() {
-      const calendar = GetSlot(this, CALENDAR);
-      const dateTime = ES.GetTemporalDateTimeFor(GetSlot(this, TIME_ZONE), GetSlot(this, INSTANT), calendar);
-      return calendar.era(dateTime);
-    },
-    configurable: true
-  });
-}
-
 // Implementation details for Gregorian calendar
 const gre = {
   isoYear(year, era) {
@@ -469,7 +451,6 @@ const gre = {
 class Gregorian extends ISO8601Calendar {
   constructor() {
     super('gregory');
-    addEraProperties();
   }
 
   era(date) {
@@ -567,7 +548,6 @@ const jpn = {
 class Japanese extends ISO8601Calendar {
   constructor() {
     super('japanese');
-    addEraProperties();
   }
 
   era(date) {

polyfill/lib/plaindate.mjs

@@ -61,6 +61,10 @@ export class PlainDate {
     if (!ES.IsTemporalDate(this)) throw new TypeError('invalid receiver');
     return GetSlot(this, CALENDAR);
   }
+  get era() {
+    if (!ES.IsTemporalDate(this)) throw new TypeError('invalid receiver');
+    return GetSlot(this, CALENDAR).era(this);
+  }
   get year() {
     if (!ES.IsTemporalDate(this)) throw new TypeError('invalid receiver');
     return GetSlot(this, CALENDAR).year(this);

polyfill/lib/plaindatetime.mjs

@@ -151,6 +151,10 @@ export class PlainDateTime {
     if (!ES.IsTemporalDateTime(this)) throw new TypeError('invalid receiver');
     return GetSlot(this, CALENDAR).nanosecond(this);
   }
+  get era() {
+    if (!ES.IsTemporalDateTime(this)) throw new TypeError('invalid receiver');
+    return GetSlot(this, CALENDAR).era(this);
+  }
   get dayOfWeek() {
     if (!ES.IsTemporalDateTime(this)) throw new TypeError('invalid receiver');
     return GetSlot(this, CALENDAR).dayOfWeek(this);

polyfill/lib/plainyearmonth.mjs

@@ -68,6 +68,10 @@ export class PlainYearMonth {
     if (!ES.IsTemporalYearMonth(this)) throw new TypeError('invalid receiver');
     return GetSlot(this, CALENDAR);
   }
+  get era() {
+    if (!ES.IsTemporalYearMonth(this)) throw new TypeError('invalid receiver');
+    return GetSlot(this, CALENDAR).era(this);
+  }
   get daysInMonth() {
     if (!ES.IsTemporalYearMonth(this)) throw new TypeError('invalid receiver');
     return GetSlot(this, CALENDAR).daysInMonth(this);

polyfill/lib/zoneddatetime.mjs

@@ -98,6 +98,10 @@ export class ZonedDateTime {
     if (!ES.IsTemporalZonedDateTime(this)) throw new TypeError('invalid receiver');
     return GetSlot(dateTime(this), ISO_NANOSECOND);
   }
+  get era() {
+    if (!ES.IsTemporalZonedDateTime(this)) throw new TypeError('invalid receiver');
+    return GetSlot(this, CALENDAR).era(dateTime(this));
+  }
   get epochSeconds() {
     if (!ES.IsTemporalZonedDateTime(this)) throw new TypeError('invalid receiver');
     const value = GetSlot(this, EPOCHNANOSECONDS);

polyfill/test/calendar.mjs

@@ -52,6 +52,9 @@ describe('Calendar', () => {
       it('Calendar.prototype.day is a Function', () => {
         equal(typeof Calendar.prototype.day, 'function');
       });
+      it('Calendar.prototype.era is a Function', () => {
+        equal(typeof Calendar.prototype.era, 'function');
+      });
       it('Calendar.prototype.dayOfWeek is a Function', () => {
         equal(typeof Calendar.prototype.dayOfWeek, 'function');
       });