LibJS: Implement Temporal.PlainMonthDay.prototype.day

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/c2ed3ad66bf
Pull-request: https://github.com/SerenityOS/serenity/pull/9429
Reviewed-by: https://github.com/IdanHo ✅

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

@@ -29,6 +29,7 @@ void PlainMonthDayPrototype::initialize(GlobalObject& global_object)
 
     define_native_accessor(vm.names.calendar, calendar_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.monthCode, month_code_getter, {}, Attribute::Configurable);
+    define_native_accessor(vm.names.day, day_getter, {}, Attribute::Configurable);
 }
 
 static PlainMonthDay* typed_this(GlobalObject& global_object)
@@ -73,4 +74,20 @@ JS_DEFINE_NATIVE_FUNCTION(PlainMonthDayPrototype::month_code_getter)
     return js_string(vm, calendar_month_code(global_object, calendar, *month_day));
 }
 
+// 10.3.5 get Temporal.PlainMonthDay.prototype.day, https://tc39.es/proposal-temporal/#sec-get-temporal.plainmonthday.prototype.day
+JS_DEFINE_NATIVE_FUNCTION(PlainMonthDayPrototype::day_getter)
+{
+    // 1. Let monthDay be the this value.
+    // 2. Perform ? RequireInternalSlot(monthDay, [[InitializedTemporalMonthDay]]).
+    auto* month_day = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let calendar be monthDay.[[Calendar]].
+    auto& calendar = month_day->calendar();
+
+    // 4. Return 𝔽(? CalendarDay(calendar, monthDay)).
+    return Value(calendar_day(global_object, calendar, *month_day));
+}
+
 }

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

@@ -21,6 +21,7 @@ public:
 private:
     JS_DECLARE_NATIVE_FUNCTION(calendar_getter);
     JS_DECLARE_NATIVE_FUNCTION(month_code_getter);
+    JS_DECLARE_NATIVE_FUNCTION(day_getter);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainMonthDay/PlainMonthDay.prototype.day.js

@@ -0,0 +1,14 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const plainMonthDay = new Temporal.PlainMonthDay(7, 6);
+        expect(plainMonthDay.day).toBe(6);
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.PlainMonthDay object", () => {
+        expect(() => {
+            Reflect.get(Temporal.PlainMonthDay.prototype, "day", "foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.PlainMonthDay");
+    });
+});