LibJS: Implement Intl.DisplayNames.prototype.resolvedOptions

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -263,6 +263,7 @@ namespace JS {
     P(length)                                \
     P(link)                                  \
     P(load)                                  \
+    P(locale)                                \
     P(localeCompare)                         \
     P(localeMatcher)                         \
     P(log)                                   \
@@ -323,6 +324,7 @@ namespace JS {
     P(reject)                                \
     P(repeat)                                \
     P(resolve)                               \
+    P(resolvedOptions)                       \
     P(reverse)                               \
     P(revocable)                             \
     P(revoke)                                \

Userland/Libraries/LibJS/Runtime/Intl/DisplayNamesPrototype.cpp

@@ -46,6 +46,7 @@ void DisplayNamesPrototype::initialize(GlobalObject& global_object)
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.of, of, 1, attr);
+    define_native_function(vm.names.resolvedOptions, resolved_options, 0, attr);
 }
 
 // 12.4.3 Intl.DisplayNames.prototype.of ( code ), https://tc39.es/ecma402/#sec-Intl.DisplayNames.prototype.of
@@ -99,4 +100,30 @@ JS_DEFINE_NATIVE_FUNCTION(DisplayNamesPrototype::of)
     return js_undefined();
 }
 
+// 12.4.4 Intl.DisplayNames.prototype.resolvedOptions ( ), https://tc39.es/ecma402/#sec-Intl.DisplayNames.prototype.resolvedOptions
+JS_DEFINE_NATIVE_FUNCTION(DisplayNamesPrototype::resolved_options)
+{
+    // 1. Let displayNames be this value.
+    // 2. Perform ? RequireInternalSlot(displayNames, [[InitializedDisplayNames]]).
+    auto* display_names = typed_this(global_object);
+    if (!display_names)
+        return {};
+
+    // 3. Let options be ! OrdinaryObjectCreate(%Object.prototype%).
+    auto* options = Object::create(global_object, global_object.object_prototype());
+
+    // 4. For each row of Table 8, except the header row, in table order, do
+    //     a. Let p be the Property value of the current row.
+    //     b. Let v be the value of displayNames's internal slot whose name is the Internal Slot value of the current row.
+    //     c. Assert: v is not undefined.
+    //     d. Perform ! CreateDataPropertyOrThrow(options, p, v).
+    options->create_data_property_or_throw(vm.names.locale, js_string(vm, display_names->locale()));
+    options->create_data_property_or_throw(vm.names.style, js_string(vm, display_names->style_string()));
+    options->create_data_property_or_throw(vm.names.type, js_string(vm, display_names->type_string()));
+    options->create_data_property_or_throw(vm.names.fallback, js_string(vm, display_names->fallback_string()));
+
+    // 5. Return options.
+    return options;
+}
+
 }

Userland/Libraries/LibJS/Runtime/Intl/DisplayNamesPrototype.h

@@ -20,6 +20,7 @@ public:
 
 private:
     JS_DECLARE_NATIVE_FUNCTION(of);
+    JS_DECLARE_NATIVE_FUNCTION(resolved_options);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Intl/DisplayNames/DisplayNames.prototype.resolvedOptions.js

@@ -0,0 +1,31 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Intl.DisplayNames.prototype.resolvedOptions).toHaveLength(0);
+    });
+
+    test("all valid types", () => {
+        const en = new Intl.DisplayNames("en", { type: "region" });
+        expect(en.resolvedOptions()).toEqual({
+            locale: "en",
+            style: "long",
+            type: "region",
+            fallback: "code",
+        });
+
+        const es419 = new Intl.DisplayNames("es-419", { type: "script", fallback: "none" });
+        expect(es419.resolvedOptions()).toEqual({
+            locale: "es-419",
+            style: "long",
+            type: "script",
+            fallback: "none",
+        });
+
+        const zhHant = new Intl.DisplayNames(["zh-Hant"], { type: "language", style: "short" });
+        expect(zhHant.resolvedOptions()).toEqual({
+            locale: "zh-Hant",
+            style: "short",
+            type: "language",
+            fallback: "code",
+        });
+    });
+});