LibJS: Implement Temporal.ZonedDateTime.prototype.toPlainMonthDay()

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

@@ -67,6 +67,7 @@ void ZonedDateTimePrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.toPlainTime, to_plain_time, 0, attr);
     define_native_function(vm.names.toPlainDateTime, to_plain_date_time, 0, attr);
     define_native_function(vm.names.toPlainYearMonth, to_plain_year_month, 0, attr);
+    define_native_function(vm.names.toPlainMonthDay, to_plain_month_day, 0, attr);
     define_native_function(vm.names.getISOFields, get_iso_fields, 0, attr);
 }
 
@@ -834,6 +835,43 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::to_plain_year_month)
     return year_month_from_fields(global_object, calendar, *fields);
 }
 
+// 6.3.51 Temporal.ZonedDateTime.prototype.toPlainMonthDay ( ), https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype.toplainmonthday
+JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::to_plain_month_day)
+{
+    // 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 temporalDateTime be ? BuiltinTimeZoneGetPlainDateTimeFor(timeZone, instant, calendar).
+    auto* temporal_date_time = builtin_time_zone_get_plain_date_time_for(global_object, &time_zone, *instant, calendar);
+    if (vm.exception())
+        return {};
+
+    // 7. Let fieldNames be ? CalendarFields(calendar, « "day", "monthCode" »).
+    auto field_names = calendar_fields(global_object, calendar, { "day"sv, "monthCode"sv });
+    if (vm.exception())
+        return {};
+
+    // 8. Let fields be ? PrepareTemporalFields(temporalDateTime, fieldNames, «»).
+    auto* fields = prepare_temporal_fields(global_object, *temporal_date_time, field_names, {});
+    if (vm.exception())
+        return {};
+
+    // 9. Return ? MonthDayFromFields(calendar, fields).
+    return month_day_from_fields(global_object, calendar, *fields);
+}
+
 // 6.3.52 Temporal.ZonedDateTime.prototype.getISOFields ( ), https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype.getisofields
 JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::get_iso_fields)
 {

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

@@ -51,6 +51,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(to_plain_time);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_date_time);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_year_month);
+    JS_DECLARE_NATIVE_FUNCTION(to_plain_month_day);
     JS_DECLARE_NATIVE_FUNCTION(get_iso_fields);
 };
 

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

@@ -0,0 +1,14 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.ZonedDateTime.prototype.toPlainMonthDay).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const timeZone = new Temporal.TimeZone("UTC");
+        const zonedDateTime = new Temporal.ZonedDateTime(1625614921000000000n, timeZone);
+        const plainMonthDay = zonedDateTime.toPlainMonthDay();
+        expect(plainMonthDay.calendar).toBe(zonedDateTime.calendar);
+        expect(plainMonthDay.monthCode).toBe("M07");
+        expect(plainMonthDay.day).toBe(6);
+    });
+});