LibJS: Implement Temporal.Calendar.prototype.monthCode

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

@@ -489,4 +489,19 @@ u8 iso_month(Object& temporal_object)
     VERIFY_NOT_REACHED();
 }
 
+// 12.1.43 ISOMonthCode ( temporalObject ), https://tc39.es/proposal-temporal/#sec-temporal-isomonthcode
+String iso_month_code(Object& temporal_object)
+{
+    // 1. Assert: temporalObject has an [[ISOMonth]] internal slot.
+    // NOTE: Asserted by the VERIFY_NOT_REACHED at the end
+
+    // 2. Return ! BuildISOMonthCode(temporalObject.[[ISOMonth]]).
+    // TODO: add the rest of the builtins with a [[ISOMonth]] slot (PlainYearMonth, PlainMonthDay)
+    if (is<PlainDate>(temporal_object))
+        return build_iso_month_code(static_cast<PlainDate&>(temporal_object).iso_month());
+    if (is<PlainDateTime>(temporal_object))
+        return build_iso_month_code(static_cast<PlainDateTime&>(temporal_object).iso_month());
+    VERIFY_NOT_REACHED();
+}
+
 }

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

@@ -48,5 +48,6 @@ double resolve_iso_month(GlobalObject&, Object& fields);
 Optional<TemporalDate> iso_date_from_fields(GlobalObject&, Object& fields, Object& options);
 i32 iso_year(Object& temporal_object);
 u8 iso_month(Object& temporal_object);
+String iso_month_code(Object& temporal_object);
 
 }

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

@@ -33,6 +33,7 @@ void CalendarPrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.dateFromFields, date_from_fields, 2, attr);
     define_native_function(vm.names.year, year, 1, attr);
     define_native_function(vm.names.month, month, 1, attr);
+    define_native_function(vm.names.monthCode, month_code, 1, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
     define_native_function(vm.names.toJSON, to_json, 0, attr);
 }
@@ -152,6 +153,33 @@ JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::month)
     return Value(iso_month(temporal_date_like.as_object()));
 }
 
+// 12.4.11 Temporal.Calendar.prototype.monthCode ( temporalDateLike ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.monthcode
+// NOTE: This is the minimum monthCode implementation for engines without ECMA-402.
+JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::month_code)
+{
+    // 1. Let calendar be the this value.
+    // 2. Perform ? RequireInternalSlot(calendar, [[InitializedTemporalCalendar]]).
+    auto* calendar = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Assert: calendar.[[Identifier]] is "iso8601".
+    VERIFY(calendar->identifier() == "iso8601"sv);
+
+    auto temporal_date_like = vm.argument(0);
+    // 4. If Type(temporalDateLike) is not Object or temporalDateLike does not have an [[InitializedTemporalDate]], [[InitializedTemporalMonthDay]], or [[InitializedTemporalYearMonth]] internal slot, then
+    // TODO PlainMonthDay & PlainYearMonth objects
+    if (!temporal_date_like.is_object() || !is<PlainDate>(temporal_date_like.as_object())) {
+        // a. Set temporalDateLike to ? ToTemporalDate(temporalDateLike).
+        temporal_date_like = to_temporal_date(global_object, temporal_date_like);
+        if (vm.exception())
+            return {};
+    }
+
+    // 5. Return ! ISOMonthCode(temporalDateLike).
+    return js_string(vm, iso_month_code(temporal_date_like.as_object()));
+}
+
 // 12.4.23 Temporal.Calendar.prototype.toString ( ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.tostring
 JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::to_string)
 {

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

@@ -23,6 +23,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(date_from_fields);
     JS_DECLARE_NATIVE_FUNCTION(year);
     JS_DECLARE_NATIVE_FUNCTION(month);
+    JS_DECLARE_NATIVE_FUNCTION(month_code);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_json);
 };

Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.monthCode.js

@@ -0,0 +1,11 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Calendar.prototype.monthCode).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const date = new Temporal.PlainDate(2021, 7, 23);
+        expect(calendar.monthCode(date)).toBe("M07");
+    });
+});