LibJS: Implement Temporal.ZonedDateTime.prototype.offset

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/6c345c8107b
Pull-request: https://github.com/SerenityOS/serenity/pull/9213
Reviewed-by: https://github.com/IdanHo ✅

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -283,6 +283,7 @@ namespace JS {
     P(next)                                  \
     P(now)                                   \
     P(of)                                    \
+    P(offset)                                \
     P(offsetNanoseconds)                     \
     P(ownKeys)                               \
     P(padEnd)                                \

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

@@ -416,7 +416,7 @@ double get_offset_nanoseconds_for(GlobalObject& global_object, Value time_zone,
 }
 
 // 11.6.12 BuiltinTimeZoneGetOffsetStringFor ( timeZone, instant )
-Optional<String> builtin_time_zone_get_offset_string_for(GlobalObject& global_object, TimeZone& time_zone, Instant& instant)
+Optional<String> builtin_time_zone_get_offset_string_for(GlobalObject& global_object, Object& time_zone, Instant& instant)
 {
     auto& vm = global_object.vm();
 

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

@@ -43,7 +43,7 @@ double parse_time_zone_offset_string(GlobalObject&, String const&);
 String format_time_zone_offset_string(double offset_nanoseconds);
 Object* to_temporal_time_zone(GlobalObject&, Value temporal_time_zone_like);
 double get_offset_nanoseconds_for(GlobalObject&, Value time_zone, Instant&);
-Optional<String> builtin_time_zone_get_offset_string_for(GlobalObject&, TimeZone&, Instant&);
+Optional<String> builtin_time_zone_get_offset_string_for(GlobalObject&, Object& time_zone, Instant&);
 PlainDateTime* builtin_time_zone_get_plain_date_time_for(GlobalObject&, Value time_zone, Instant&, Object& calendar);
 
 bool is_valid_time_zone_numeric_utc_offset_syntax(String const&);

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

@@ -55,6 +55,7 @@ void ZonedDateTimePrototype::initialize(GlobalObject& global_object)
     define_native_accessor(vm.names.monthsInYear, months_in_year_getter, {}, Attribute::Configurable);
     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);
 }
 
 static ZonedDateTime* typed_this(GlobalObject& global_object)
@@ -671,4 +672,23 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::offset_nanoseconds_getter)
     return Value(get_offset_nanoseconds_for(global_object, &time_zone, *instant));
 }
 
+// 6.3.29 get Temporal.ZonedDateTime.prototype.offset, https://tc39.es/proposal-temporal/#sec-get-temporal.zoneddatetime.prototype.offset
+JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::offset_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 instant be ! CreateTemporalInstant(zonedDateTime.[[Nanoseconds]]).
+    auto* instant = create_temporal_instant(global_object, zoned_date_time->nanoseconds());
+
+    // 4. Return ? BuiltinTimeZoneGetOffsetStringFor(zonedDateTime.[[TimeZone]], instant).
+    auto offset_string = builtin_time_zone_get_offset_string_for(global_object, zoned_date_time->time_zone(), *instant);
+    if (vm.exception())
+        return {};
+    return js_string(vm, move(*offset_string));
+}
+
 }

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

@@ -44,6 +44,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(months_in_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(in_leap_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(offset_nanoseconds_getter);
+    JS_DECLARE_NATIVE_FUNCTION(offset_getter);
 };
 
 }

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

@@ -0,0 +1,21 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const timeZone = new Temporal.TimeZone("UTC");
+        const zonedDateTime = new Temporal.ZonedDateTime(0n, timeZone);
+        expect(zonedDateTime.offset).toBe("+00:00");
+    });
+
+    test("custom offset", () => {
+        const timeZone = new Temporal.TimeZone("+01:30");
+        const zonedDateTime = new Temporal.ZonedDateTime(0n, timeZone);
+        expect(zonedDateTime.offset).toBe("+01:30");
+    });
+});
+
+test("errors", () => {
+    test("this value must be a Temporal.ZonedDateTime object", () => {
+        expect(() => {
+            Reflect.get(Temporal.ZonedDateTime.prototype, "offset", "foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.ZonedDateTime");
+    });
+});