LibJS: Implement Temporal.Instant.prototype.epochNanoseconds

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -115,6 +115,7 @@ namespace JS {
     P(enumerable)                            \
     P(epochMicroseconds)                     \
     P(epochMilliseconds)                     \
+    P(epochNanoseconds)                      \
     P(epochSeconds)                          \
     P(error)                                 \
     P(errors)                                \

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

@@ -26,6 +26,7 @@ void InstantPrototype::initialize(GlobalObject& global_object)
     define_native_accessor(vm.names.epochSeconds, epoch_seconds_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.epochMilliseconds, epoch_milliseconds_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.epochMicroseconds, epoch_microseconds_getter, {}, Attribute::Configurable);
+    define_native_accessor(vm.names.epochNanoseconds, epoch_nanoseconds_getter, {}, Attribute::Configurable);
 
     // 8.3.2 Temporal.Instant.prototype[ @@toStringTag ], https://tc39.es/proposal-temporal/#sec-temporal.instant.prototype-@@tostringtag
     define_direct_property(*vm.well_known_symbol_to_string_tag(), js_string(vm.heap(), "Temporal.Instant"), Attribute::Configurable);
@@ -101,4 +102,20 @@ JS_DEFINE_NATIVE_FUNCTION(InstantPrototype::epoch_microseconds_getter)
     return js_bigint(vm.heap(), move(us));
 }
 
+// 8.3.6 get Temporal.Instant.prototype.epochNanoseconds, https://tc39.es/proposal-temporal/#sec-get-temporal.instant.prototype.epochnanoseconds
+JS_DEFINE_NATIVE_FUNCTION(InstantPrototype::epoch_nanoseconds_getter)
+{
+    // 1. Let instant be the this value.
+    // 2. Perform ? RequireInternalSlot(instant, [[InitializedTemporalInstant]]).
+    auto* instant = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let ns be instant.[[Nanoseconds]].
+    auto& ns = instant->nanoseconds();
+
+    // 4. Return ns.
+    return &ns;
+}
+
 }

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

@@ -22,6 +22,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(epoch_seconds_getter);
     JS_DECLARE_NATIVE_FUNCTION(epoch_milliseconds_getter);
     JS_DECLARE_NATIVE_FUNCTION(epoch_microseconds_getter);
+    JS_DECLARE_NATIVE_FUNCTION(epoch_nanoseconds_getter);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Temporal/Instant/Instant.prototype.epochNanoseconds.js

@@ -0,0 +1,25 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        expect(new Temporal.Instant(0n).epochNanoseconds).toBe(0n);
+        expect(new Temporal.Instant(1n).epochNanoseconds).toBe(1n);
+        expect(new Temporal.Instant(999n).epochNanoseconds).toBe(999n);
+        expect(new Temporal.Instant(8_640_000_000_000_000_000_000n).epochNanoseconds).toBe(
+            8_640_000_000_000_000_000_000n
+        );
+
+        expect(new Temporal.Instant(-0n).epochNanoseconds).toBe(-0n);
+        expect(new Temporal.Instant(-1n).epochNanoseconds).toBe(-1n);
+        expect(new Temporal.Instant(-999n).epochNanoseconds).toBe(-999n);
+        expect(new Temporal.Instant(-8_640_000_000_000_000_000_000n).epochNanoseconds).toBe(
+            -8_640_000_000_000_000_000_000n
+        );
+    });
+});
+
+test("errors", () => {
+    test("this value must be a Temporal.Instant object", () => {
+        expect(() => {
+            Reflect.get(Temporal.Instant.prototype, "epochNanoseconds", "foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.Instant");
+    });
+});