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

3 files changed, 41 insertions, 0 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.cpp
index 4b595744ff..fcd3ed8cde 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.cpp
@@ -56,6 +56,7 @@ void PlainDateTimePrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.valueOf, value_of, 0, attr);
     define_native_function(vm.names.toPlainDate, to_plain_date, 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.toPlainTime, to_plain_time, 0, attr);
     define_native_function(vm.names.getISOFields, get_iso_fields, 0, attr);
 }
@@ -444,6 +445,32 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDateTimePrototype::to_plain_year_month)
     return year_month_from_fields(global_object, calendar, *fields);
 }
 
+// 5.3.39 Temporal.PlainDateTime.prototype.toPlainMonthDay ( ), https://tc39.es/proposal-temporal/#sec-temporal.plaindatetime.prototype.toplainmonthday
+JS_DEFINE_NATIVE_FUNCTION(PlainDateTimePrototype::to_plain_month_day)
+{
+    // 1. Let dateTime be the this value.
+    // 2. Perform ? RequireInternalSlot(dateTime, [[InitializedTemporalDateTime]]).
+    auto* date_time = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let calendar be dateTime.[[Calendar]].
+    auto& calendar = date_time->calendar();
+
+    // 4. Let fieldNames be ? CalendarFields(calendar, « "day", "monthCode" »).
+    auto field_names = calendar_fields(global_object, calendar, { "day"sv, "monthCode"sv });
+    if (vm.exception())
+        return {};
+
+    // 5. Let fields be ? PrepareTemporalFields(dateTime, fieldNames, «»).
+    auto* fields = prepare_temporal_fields(global_object, *date_time, field_names, {});
+    if (vm.exception())
+        return {};
+
+    // 6. Return ? MonthDayFromFields(calendar, fields).
+    return month_day_from_fields(global_object, calendar, *fields);
+}
+
 // 5.3.40 Temporal.PlainDateTime.prototype.toPlainTime ( ), https://tc39.es/proposal-temporal/#sec-temporal.plaindatetime.prototype.toplaintime
 JS_DEFINE_NATIVE_FUNCTION(PlainDateTimePrototype::to_plain_time)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.h b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.h
index 4d377cdf04..ed64b8fad6 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDateTimePrototype.h
@@ -43,6 +43,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(value_of);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_date);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_year_month);
+    JS_DECLARE_NATIVE_FUNCTION(to_plain_month_day);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_time);
     JS_DECLARE_NATIVE_FUNCTION(get_iso_fields);
 };
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDateTime/PlainDateTime.prototype.toPlainMonthDay.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDateTime/PlainDateTime.prototype.toPlainMonthDay.js
new file mode 100644
index 0000000000..6b52cdbd4f
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDateTime/PlainDateTime.prototype.toPlainMonthDay.js
@@ -0,0 +1,13 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.PlainDateTime.prototype.toPlainMonthDay).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const plainDateTime = new Temporal.PlainDateTime(2021, 7, 6, 18, 14, 47);
+        const plainMonthDay = plainDateTime.toPlainMonthDay();
+        expect(plainMonthDay.calendar).toBe(plainDateTime.calendar);
+        expect(plainMonthDay.monthCode).toBe("M07");
+        expect(plainMonthDay.day).toBe(6);
+    });
+});