LibJS: Implement Temporal.ZonedDateTime.prototype.era

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/b59e9260db2
Pull-request: https://github.com/SerenityOS/serenity/pull/9647
Reviewed-by: https://github.com/IdanHo ✅

Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp

@@ -59,6 +59,7 @@ void ZonedDateTimePrototype::initialize(GlobalObject& global_object)
     define_native_accessor(vm.names.inLeapYear, in_leap_year_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.offsetNanoseconds, offset_nanoseconds_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.offset, offset_getter, {}, Attribute::Configurable);
+    define_native_accessor(vm.names.era, era_getter, {}, Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.valueOf, value_of, 0, attr);
@@ -704,6 +705,33 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::offset_getter)
     return js_string(vm, move(*offset_string));
 }
 
+// 15.6.10.2 get Temporal.ZonedDateTime.prototype.era, https://tc39.es/proposal-temporal/#sec-get-temporal.zoneddatetime.prototype.era
+JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::era_getter)
+{
+    // 1. Let zonedDateTime be the this value.
+    // 2. Perform ? RequireInternalSlot(zonedDateTime, [[InitializedTemporalZonedDateTime]]).
+    auto* zoned_date_time = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let timeZone be zonedDateTime.[[TimeZone]].
+    auto& time_zone = zoned_date_time->time_zone();
+
+    // 4. Let instant be ! CreateTemporalInstant(zonedDateTime.[[Nanoseconds]]).
+    auto* instant = create_temporal_instant(global_object, zoned_date_time->nanoseconds());
+
+    // 5. Let calendar be zonedDateTime.[[Calendar]].
+    auto& calendar = zoned_date_time->calendar();
+
+    // 6. Let plainDateTime be ? BuiltinTimeZoneGetPlainDateTimeFor(timeZone, instant, calendar).
+    auto* plain_date_time = builtin_time_zone_get_plain_date_time_for(global_object, &time_zone, *instant, calendar);
+    if (vm.exception())
+        return {};
+
+    // 7. Return ? CalendarEra(calendar, plainDateTime).
+    return calendar_era(global_object, calendar, *plain_date_time);
+}
+
 // 6.3.44 Temporal.ZonedDateTime.prototype.valueOf ( ), https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype.valueof
 JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::value_of)
 {

Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h

@@ -45,6 +45,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(in_leap_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(offset_nanoseconds_getter);
     JS_DECLARE_NATIVE_FUNCTION(offset_getter);
+    JS_DECLARE_NATIVE_FUNCTION(era_getter);
     JS_DECLARE_NATIVE_FUNCTION(value_of);
     JS_DECLARE_NATIVE_FUNCTION(to_instant);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_date);

Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.era.js

@@ -0,0 +1,26 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const timeZone = new Temporal.TimeZone("UTC");
+        const zonedDateTime = new Temporal.ZonedDateTime(1625614921000000000n, timeZone);
+        expect(zonedDateTime.era).toBeUndefined();
+    });
+
+    test("calendar with custom era function", () => {
+        const timeZone = new Temporal.TimeZone("UTC");
+        const calendar = {
+            era() {
+                return "foo";
+            },
+        };
+        const zonedDateTime = new Temporal.ZonedDateTime(1625614921000000000n, timeZone, calendar);
+        expect(zonedDateTime.era).toBe("foo");
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.ZonedDateTime object", () => {
+        expect(() => {
+            Reflect.get(Temporal.ZonedDateTime.prototype, "era", "foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.ZonedDateTime");
+    });
+});