LibJS: Implement Temporal.Instant.prototype.toLocaleString()

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

@@ -41,6 +41,7 @@ void InstantPrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.round, round, 1, attr);
     define_native_function(vm.names.equals, equals, 1, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
+    define_native_function(vm.names.toLocaleString, to_locale_string, 0, attr);
     define_native_function(vm.names.valueOf, value_of, 0, attr);
 }
 
@@ -335,6 +336,24 @@ JS_DEFINE_NATIVE_FUNCTION(InstantPrototype::to_string)
     return js_string(vm, *string);
 }
 
+// 8.3.14 Temporal.Instant.prototype.toLocaleString ( [ locales [ , options ] ] ), https://tc39.es/proposal-temporal/#sec-temporal.instant.prototype.tolocalestring
+// NOTE: This is the minimum toLocaleString implementation for engines without ECMA-402.
+JS_DEFINE_NATIVE_FUNCTION(InstantPrototype::to_locale_string)
+{
+    // 1. Let instant be the this value.
+    // 2. Perform ? RequireInternalSlot(instant, [[InitializedTemporalInstant]]).
+    auto* instant = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Return ? TemporalInstantToString(instant, undefined, "auto").
+    auto string = temporal_instant_to_string(global_object, *instant, js_undefined(), String { "auto"sv });
+    if (vm.exception())
+        return {};
+
+    return js_string(vm, *string);
+}
+
 // 8.3.16 Temporal.Instant.prototype.valueOf ( ), https://tc39.es/proposal-temporal/#sec-temporal.instant.prototype.valueof
 JS_DEFINE_NATIVE_FUNCTION(InstantPrototype::value_of)
 {

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

@@ -28,6 +28,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(round);
     JS_DECLARE_NATIVE_FUNCTION(equals);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
+    JS_DECLARE_NATIVE_FUNCTION(to_locale_string);
     JS_DECLARE_NATIVE_FUNCTION(value_of);
 };
 

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

@@ -0,0 +1,18 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.Instant.prototype.toLocaleString).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const instant = new Temporal.Instant(1625614921123456789n);
+        expect(instant.toLocaleString()).toBe("2021-07-06T23:42:01.123456789Z");
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.Instant object", () => {
+        expect(() => {
+            Temporal.Instant.prototype.toLocaleString.call("foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.Instant");
+    });
+});